Making more work for yourself reminded me of my power supply repair nightmare. I was fixing a 35 year old power supply missing a power resistor that had fallen off and vanished in shipment, when I stupidly replaced the resistor with a very wrong value replacement, which then destroyed the chopper transistor, a vendor marked high voltage bipolar transistor. I spent ages reverse engineering the thing to figure out the characteristics of the transistor, and was about to give up. The one night I had an epiphany: why not just contact the original power supply vendor. They had been acquired by another company, so I contacted them. The new company had nothing for my OEM part number, so I searched eBay for similar generic versions of the same power supplies from the same company. I sent them one of those part numbers, and they sent me a cropped screenshot of the original BOM, showing that it was an 850V 10A NPN transistor, 10 minutes later I had a replacement in the way. The moral of the story: sometimes it‘s smart to just ask!
Awesome! I repair solar diverters and when I contacted the manufacturer for the schematics they said the same thing. "sorry not available". So it was out with the pen and paper and work out the circuit. It's satisfying to find a blown mosfet driver, bridge or series of casualties and get it back to working order. That series of videos was great to watch and helpful to someone like me, Thanks for taking the time to record, edit and share your work.
Brilliant series Marc as per usual. Takes me back to the 70’s and 80’s when I was doing TV servicing SMPS were my pet hate. We had a multimeter and were luck to have a CRO but no HV differential probes and the like. Every make and model seem to have variants of start ups, switching and minds of their own! 😀 Your 4 part series highlighted why in a situation where the customer is paying and typically not want to pay much it was better outcome for both to swap a SMPS module out. We did have a technician who mentored me through my apprenticeship who was a savant with SMPS....not even he made me comfortable fixing SMPS apart from the list he kept of common problems he found with certain supplies. You could spend 30 minutes on looking at him common fault list invariably you would swap out what was on his list a viola.....but if that didn’t fix it swap out and take back where he would add that fault to his list. Fascinating series you put together reminding me in part why I don’t like SMPS. 😀 I like the amount of available HP technology you have in your workshop and your tireless approach to working through with knowledge and equipment to get a result. Thanks for sharing...
Loved this series of 'fault finding' vlogs. The key 'take a way' for me, is that this does not look like an HP power supply as I recognise it. It was not designed properly in the first place, (it was not designed 'the way an engineer' would do it). A well engineered product can be 're-engineered', but also is designed to be tested and repaired - which certainly doesn't seem to be the case here. Bravo you for getting to the 'finish line'! How sad to see a symptom of HPs decline after so many years of excellence. As this product was being shipped, I moved from HP to IBM, and then later 'onwards'.
Default TH-camr: Let's build something useless out of clay and hot-glue... CuriousMarc: Let's re-engeneer and repair irreplaceable, highly-sophisticated vintage equipment (from lab devices to the AGC) You're one of the most awesome hoarders I've seen so far, thank you for sharing it!
Congratulations on rescuing another rare piece of HP kit! I spent about a decade and a half with HP/Agilent labs. I too have an affinity for older, serviceable test equipment. As I got interested in a particular piece of equipment, I'd talk to folks in Labs who had been there almost forever -- what can you tell me about this thing? I'd get all kinds of stories, occasionally the names of key engineers. Got solid advice on what to avoid (usually because a key component was both failure prone and unobtanium), and what was good. Occasionally I even listened to the advice I was given. I did learn that slug tantalum caps have no sense of humor and don't age well.
It's so frustrating not being able to obtain schematics. It's not like this kit is new, just bloody minded manufacturers protecting obsolete IP. Good work Mark. Credit where it's due.
To watch such an engineer as CuriousMarc, with such an equipment and all his experience, struggling to understand and fix a power supply makes me feel so confident, I have months fighting with a TV lamps power supply, thank you CuriousMarc
Have you considered using sockets for the 8 pin DIP IC's? I recently repaired the linear regulator board (card A8) on an HP8720C, it had a 'weak' linear IC where the beta of its output transistor had been reduced over the years. I found that socketing some of the key IC's was handy for troubleshooting and comparing adjacent IC's to each other. Great repair video series, thank you very much for taking on that switching power supply and showing us all how you got it to work again!
...and the next time you have a similar PSU fault, you will remember that it might not behave unless under the correct load. That's why fault chasing like this should be thought of as a learning experience, and not wasted time. A thoroughly enjoyable series. Sending the same wishes back to you and yours at this difficult time.
Back in the 80's we quickly learnt not to try power up an Apple II switchmode power supply without a load. It would immediately "hiccup" sounding as if it was overloaded. Nice diagnosis for the HP.
Thoroughly enjoyable to watch as my technician brain tried to keep up with your thought processes. I know you're very familiar with your test equip, but the way your fingers dance through all the selection keys & softkey menus to view the display you want is just like watching a musician playing an instrument.
Well done. As always, reasoning plays a big part in troubleshooting, repair and reverse engineering hardware. It has served me well for 40 years on the bench. 😃
Nice video series and very instructive, I'm pleased you fixed it, nice to see a piece of kit rescued from oblivion. I know you realised it wasn't necessary but surely logic would suggest that the only reason to modify the original design would be to mask a fault you'd not yet diagnosed? As for those in the comments who are hating on the people who suggest changing caps, you've obviously never worked in a commercial repair operation where it becomes obvious very quickly that faulty PSUs with intact fuses can be repaired by cap replacement 30-40% of the time and that it's time/cost efficient to do so, it's not approriate in all cases but it fixes a *lot* of them
I used to fix PSUs and CRTs for a living. The majority of SMPS designs use virtually the same circuit building blocks (although the buck converter block is unusual). Another cause of failures is the kick start resistor going high. For some reason this tends to result in blown MOSFETs ... the controller chip seems to lock up when it doesn't get enough current from the Kickstarter and the result is always blown FETs.
What a great series of videos! Thank you for sticking with it - most of us need help with switch-mode supplies. I have used a similar photographic technique - or possibly the same one, photographing the top and bottom of the board, flipping the bottom then adding it to the top as a layer and adjusting it's opacity. Very handy for reverse engineering undocumented boards. One key is making sure the top and bottom pictures are both taken at the same distance from the focal plane of the the camera so all traces and components are the same size. A video of your process would be interesting and probably very helpful to others.
Stellar effort! Worst supply I had was my own Sony ProFeel TV monitor (KX-27PS1) that had a weird (Sony Special) self oscillating power supply with a custom resin coated hybrid control board that injected a control signal via an extra winding on the core (ie no opto-isolator). The problem was it would randomly kill the chopper transistor on start up (once a week/month/2 months), this was a known design problem unfortunately. Even stranger part of the design was huge 50w (can't remember exactly) soft start current limiting resistor that was switched out by a relay after 1/2 a second. I ended up fixing it by adding a little more resistance to the soft start resistor to limit inrush current and then worked perfectly for years until the tube's blue gun went weak. Cheers.
I think that the optocoupler may be faulty, in that it's CTR has reduced with age. I recently learned a harsh lesson in that these components don't last forever. I'm told that the LED within the opto suffers from age-related "micro-cracks", thus reduced light output and so reduced CTR. I noticed that your opto is a 1993 vintage part - about the same age as the ones that caused me lots of grief... I think that when you removed and re-fitted the opto, the heat of the soldering process made the opto work again. I'd fit a new one , given the merry dance that I had with (six) aged optos! Many thanks for your interesting videos.
The op-amp was a very good guess. About the effect of the probes, I suspect that probes are adding stray capacitance that helped to stabilize the circuit. I had a similar experience when assembling an audio amplifier that used parallel stages, on a breadboard: all very stable and crisp. On the final PCB, not so, because it went oscillating. Fixed the issue with small caps in parallel with the feedback resistors going from the output to the inverting inputs on both power amplifiers.
Holy crap not an easy fix by any means! Wow. That trick of taking really good quality photos of the board and then mapping it out with photoshop is a brilliant idea. I'll for sure use that trick. I've got an old ATX SMPS that I use just for bench lights and a basic 5v "quick n dirty" supply for things that I took from an old computer tower and "tricked" it with a load to get it to turn all the way on. Anyhow, I measured it a while back and for some reason, I have +5, -12, +3.3 working just fine, but the +12 I threw on my strip lights is more like 11.7 or so (load or no load). Still runs my lights good enough, but never did fully probe around in there enough to find the source of that problem. Watching this make me wonder, but I fear I may be opening pandora's box after seeing what you contended with haha. Nice work, Marc. Given the equipment yours had to run, you had no choice and quite the challenge to conquer that thing.
Ah yes, the electronic repair equivalent of "when all you have is a hammer, everything looks like a nail". Having said that, I'd still swap the Rifa input caps though ;)
It took the same mind that rebuilt the Apollo AGC to fix this power supply. I don't think very many people would have been able to pull this off (at least, without many years studying power circuits). Good job!
I put my bet on the PFET in the 300V-to-100V buck converter. You're dealing with a lot of power in this supply, which will stress this FET by quite a bit. Unless that FET turns on and off very quickly (probably doesn't), the average Pd of the FET is quite high. A mistake many make when driving a PFET is putting a little R in series with the gate. This has the effect of slowing down the on/off time of the FET (Miller capacitance integrator), increasing its Pd. If it shorts out, as it did, then you tripled the input voltage to the 100V DC-DC push-pull converter, causing its outputs to triple in voltage, too. Essentially, everything downstream from the first failed converter was highly overstressed as well, and took out just about everything with it. With 20/20 hindsight from the year 2020, the supply designer should have put in some sort of OVP circuit on that 100V output. But as the expression goes, everyone is brilliant with 20/20 hindsight. Very impressive reverse engineering, Marc. I enjoyed your debug thought process and various workarounds.
A colleague and I tackled the switching power supply inside an amateur radio amplifier and that was 48v @ 48amps. The switching circuit was driven by a MA3830 multi regulator but had issues with the control circuit that ultimately led back to the power factor correction IC. The circuit would break into oscillation and to tame it he loaded the switch on and placed a constant 1 amp load on the 48v circuit. Without it the maximum the MA3830 could take was 380v and we already had 370v and coming close to the limit. As this then fed 450v capacitors with (and where Yaesu confused us) with 380v and -380v which is a potential of 760v, however it was just their way of saying 380v and 0v. After quite a few component changes we finally have 48v@48amp of very highly filtered DC from the Yaesu VP1000 power supply (25kg in weight too). Without videos to see the startup loop we would have been rather lost but the complex PFC and oscillation and the MA3830 having staggered pins from left and right in different packages really confused us too. Thank you for a really great video it was enjoyable from part 1 to part 4 and very honest. Kudos
I'm a bit behind on my viewing so I only just got round to watching parts 2, 3 and 4 - brilliant bit of fault diagnosing, great fun to watch - love the rant at the beginning of part two!!!!! I love the fact that you actually over fixed it and had to revert back to the earlier fix. Amazing set of videos, great to watch, cheers Marc.
@@CuriousMarc Your optoisolator LED+transistor gain may have gone out of original design assumed spec. When manufactured the LEDs and transistors are individual die and binned by LED emission/current (which drops over age), and similar optocoupler transistor binned by photo-gain (also changes with age and accumulated history of stress from temperature, collector current, Vce). Dealt with this many times before with with suppliers changing optocoupler die specs (manufacturers sell out HP-> Motorola->LiteOn->DiodesInc-> etc and source and bin die differently) and PSU builders substituting optocoupler versions (suppliers bought out, min gain specs get sloppy with replaced LED and transistor die, etc, and suddenly a batch of new PSUs has different load regulation characteristics). Symptoms are usually out-of control switcher feedback loops under transient or at steady low or high currents. I'd suggest Checking yours with the whole PSU under repetitive pulsed transient loading, say with constant_I of 0.5A + pulsed_I of say 1A, and look closely at the feedback via the optocoupler LED and transistor currents. I suspect that as you found there's several feedback loops summing via that resistor network. A steady (low frequency) state current feedback loop, and a dynamic loop (via the optocoupler responding switcher cycle by cycle). Your patch explained here may fix the steady state condition, but probably doesn't fix the dynamic/transient load response. Look up the original optocoupler gain spec (LED current to transistor current gain), and consider replacing it with a fresh one with at least the same gain (and suitable Vce and watch for LED die Vf and reverse breakdown if the LED die type has changed from an old GaP to AlInGaP, etc). More optocoupler gain isn't usually a problem since the LM311 should give you a square -wave drive in, but do watch where the 311's output transsitor C and E are wired and how many volts (or reverse bias) can get sent to the optocoupler LED. There may be option to push more current though the optocoupler LED and pick up some gain (but look at the datasheets, binning, and don't assume anything from the optocoupler die supplie - Perhaps stick it on that beautiful HP curve tracer :-) p.s. I love that you're doing these restorations of wonderful instruments
Great work Marc. During my many years as an electronics tech, everyone hated switched modes, except the design engineers and the production managers. I really like HP's gear but their service stinks. Recently tried to download the bios for a 10 year old server. It was right there but no, you can't have it without an active service contract.
One of my livings was running an in-house test equipment REPAIR lab with Tek, HP/Agilent/Keysight, Fluke, Sencore and other respected industrial brands of equipment. They all provided extensive detailed manuals and theory of operation. (As did Heathkit for hobbyists in their good years). I am saddened to learn that even Keysight has gone the way of planned appleescence. EVIL beancounter cancer spreads. No used market for keeping a pool of budding engineers and technicians learning. Join or make a right to repair group in your state.
Of all of the vintage equipment you could collect, test gear is the best to choose.... you never know when you'll need 4 bench power supplies AND a function generator.
I was working on a defective inverter board from my airco. Its much much simpler but i suspect a problem with the switchmode part. This video motivated to push on!
Congratulations on fixing it, it was probably a worth while experience in the amount of experience you gained. The proper loading of a SMPS has caught me off guard too and I only got the correct voltages when properly loading it around the current draw for it's intended use. Great video's I enjoyed it.
Bill Hewlett & David Packard would have been proud to see you persist and get this fixed. Two kinds of repairs that I hate are those without schematics and those with feedback loops. Reverse engineering this was a HUGE task, but I was expecting you to break the feedback loop somewhere and insert your own control signal, but with more than 1 loop, I don't know if that could have worked. Yes, it was probably the jFET opamp. Nice work, Marc! ;-)
This series was fun, as usual your channel is just at the edge of my knowledge. It's nice to have my brain pushed beyond swapping caps and have to look up a thing or two.
Sir, Thanks a lot to have shared this series of video ... whatched alll from 1 to 4 straight. it helped me a TONS to think better were to look. Again. THANKS!
What a well written thriller with cliffhangers and all. I learned a lot Marc, thanks for sharing your epic battle with us! I must admit I was cringing the whole time while you were testing/debugging with the supply unloaded. Somehow I knew that was going to bite you. 😋 Cheers! 🍻
Great video! I have a similar power supply from an HP spectrum analyser 8563A that has an issue not too dissimilar to this. Fortunatly there is a schematic. I found that most of the parts are badged with HP part numbers which makes it more problematic trying to find the actual device number.
I have also wasted time repairing a SMPSU by not having enough load on it to start up. It basically throttled back so far it didn't generate enough voltage on the auxiliary winding that powered the control chip, so it never completed the boot sequence.
Wow, this was very interesting and a nice look into the physics of switching power supplies. Did you show this to Master Ken? I bet he would like the complexity of this supply.
Fantastic,its been so educational and entertaining hearing your thought processes all the way through. A large portion of fault finding is about confusion!! if you're not comfortable with that you wont fix things,as faults aren't going to make themselves obvious,i know this from personal history. I watched episodes two and three several times,to try to understand what might be happening. After looking at them several times i thought two things:- (1)what value is Marc setting on his electronic load? I had no idea what load the power supply was expecting,and wondered if there was any indication on the case,of current and wattage so that you could set a ball park value on your electronic load setting, If no indication was given,i thought you should set various values,and slowly increase load,whilst watching regulation behaviour. (2)My other thought was, that there must be something flaky happening in the feedback path,and so the mad cappers maybe onto something after all!!! I was too chicken to send my first suggestion,after all Marc has repaired more SMPSU's than i've had hot dinners,just let him think in peace!! The Alto Power supply repair was hilarious....these power supplies are evil! The days of simple linear power supplies are gone. Terrific videos Marc,thank you for sharing,you are stimulating the noggin..
@5:48 Oh man! I have that exact same "Digi Designer"! Never seen someone else with one :) They are handy for quick little tests like that. The built in power supply and square wave generator is great.
Regarding the probes, indeed sometimes you need extra high quality ones with very low capacitance or they will increase the capacitance of the traces so that it will change the behavior of the device. Had similar issue when chasing the I2C issues and noise on the line - if the standard probes were attached the I2C line behavior changed quite a bit. It was required to use special probes to see exactly whats happening on the line.
Removing input and output caps and limiting the amps with a light bulb in series should work too. A IR camera is really helpful for finding faulty components too.
Loved your whole serie on the fixing of the SPS. learned a little trick of using photo to trace the lines with photo software very good. Will keep it for futur debugging job
And now you know why technicians have so much stuff on their benches. IT'S ALL USEFUL! "I'LL NEED IT ONE DAY!" Jimmy Diresta would be proud ("Better to have it and not need it, than to need it and not have it" - he's quoting someone else, but he lives by that idiom).
Great job, new you would find it. My guess is the PS was not an HP design but contracted out. All the HP stuff I have ever looked at for the most part follow the kiss principal, clearly it was not followed in this case.
Thinking of all the info needed to have at hand in operating this absolutely fabulous collection of vintage and up-to-date electronic instruments gives me a headache ...
I have seen several switchers be unhappy with low current loads. A few I got surplus had a minimum load listed shown on the label with the other specs. Wish I had a tracking genny that went that high in freq. My IFR only goes to 1900MHz.
This is a great series, and gives me hope that eventually I will feel confident enough to try to repair the broken PSU in my IBM 5150. I will not dare touch it until I feel I at least know the basics and how to be safe. Getting there! Like you, I'd rather not simply recap and pray; I am a huge fan of trying to understand the problem. Especially as I still have such a lot to learn and am not working to time constraints (hobby, for now). :)
To me it seemed a little bit like the optocoupler was always bad since things changed after resoldering and you never messed with it before. Assuming a single component failure, maybe this caused the DC voltage to go high and start blowing stuff up? Assuming more than one failure, surely the opamps were not good
Well done sir, I think I would have gave up on the second video. Mind you, you have all the equipment there to fix most things and also the knowledge to repair it. Very good interesting video, yes it looks like it was designed for a full load all the time. For me it is over complicated, over designed no doubt over expansive as well.
Fantastic conclusion! I try to never assume a test setup is applicable for the unit under test. If it doesn't work out of a device's normal environment, what did I do wrong in setup?
"Electroboom moment". All credits for you for inventing this term. Those power contacts on the table I have never seen them before. Which country are they from?
@16:31 - and this is what happens when you spend this long trying to fix a switch mode PSU without any documentation. Hopefully Marc will recover. :D Cheers on getting the thing going again.
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7:36 That feeling, when the code fails miserably at runtime, but performs flawlessly when debugged..
Awesome video and incredible tenacity - "Never give up. Never surrender!" 👍🏻😀
You get extra love for the Galaxy Quest reference!
Making more work for yourself reminded me of my power supply repair nightmare.
I was fixing a 35 year old power supply missing a power resistor that had fallen off and vanished in shipment, when I stupidly replaced the resistor with a very wrong value replacement, which then destroyed the chopper transistor, a vendor marked high voltage bipolar transistor. I spent ages reverse engineering the thing to figure out the characteristics of the transistor, and was about to give up.
The one night I had an epiphany: why not just contact the original power supply vendor. They had been acquired by another company, so I contacted them. The new company had nothing for my OEM part number, so I searched eBay for similar generic versions of the same power supplies from the same company. I sent them one of those part numbers, and they sent me a cropped screenshot of the original BOM, showing that it was an 850V 10A NPN transistor, 10 minutes later I had a replacement in the way.
The moral of the story: sometimes it‘s smart to just ask!
Awesome! I repair solar diverters and when I contacted the manufacturer for the schematics they said the same thing. "sorry not available". So it was out with the pen and paper and work out the circuit.
It's satisfying to find a blown mosfet driver, bridge or series of casualties and get it back to working order.
That series of videos was great to watch and helpful to someone like me, Thanks for taking the time to record, edit and share your work.
When you mentioned quantum fault diagnosis I was sure you would end up looking for Schrodinger cap.
cat
/r/whoosh
QET - Quantum Effect Transistor
Haha
I so wanted to not like that comment :) Genius ....
What a rollercoaster of a repair! Truly a solder slinger's nightmare, beaten with terminator-like determination. The more I watch the more I learn 👍
The photo of the PCB with the traces traced out in color is quite beautiful. A work of art as a byproduct of some awesome reverse engineering.
Brilliant series Marc as per usual. Takes me back to the 70’s and 80’s when I was doing TV servicing SMPS were my pet hate. We had a multimeter and were luck to have a CRO but no HV differential probes and the like. Every make and model seem to have variants of start ups, switching and minds of their own! 😀
Your 4 part series highlighted why in a situation where the customer is paying and typically not want to pay much it was better outcome for both to swap a SMPS module out. We did have a technician who mentored me through my apprenticeship who was a savant with SMPS....not even he made me comfortable fixing SMPS apart from the list he kept of common problems he found with certain supplies. You could spend 30 minutes on looking at him common fault list invariably you would swap out what was on his list a viola.....but if that didn’t fix it swap out and take back where he would add that fault to his list.
Fascinating series you put together reminding me in part why I don’t like SMPS. 😀 I like the amount of available HP technology you have in your workshop and your tireless approach to working through with knowledge and equipment to get a result. Thanks for sharing...
Loved this series of 'fault finding' vlogs. The key 'take a way' for me, is that this does not look like an HP power supply as I recognise it. It was not designed properly in the first place, (it was not designed 'the way an engineer' would do it). A well engineered product can be 're-engineered', but also is designed to be tested and repaired - which certainly doesn't seem to be the case here. Bravo you for getting to the 'finish line'! How sad to see a symptom of HPs decline after so many years of excellence. As this product was being shipped, I moved from HP to IBM, and then later 'onwards'.
A+ Repair! Thanks for sharing the journey!
Default TH-camr: Let's build something useless out of clay and hot-glue...
CuriousMarc: Let's re-engeneer and repair irreplaceable, highly-sophisticated vintage equipment (from lab devices to the AGC)
You're one of the most awesome hoarders I've seen so far, thank you for sharing it!
Congratulations on rescuing another rare piece of HP kit! I spent about a decade and a half with HP/Agilent labs. I too have an affinity for older, serviceable test equipment. As I got interested in a particular piece of equipment, I'd talk to folks in Labs who had been there almost forever -- what can you tell me about this thing? I'd get all kinds of stories, occasionally the names of key engineers. Got solid advice on what to avoid (usually because a key component was both failure prone and unobtanium), and what was good. Occasionally I even listened to the advice I was given. I did learn that slug tantalum caps have no sense of humor and don't age well.
It's so frustrating not being able to obtain schematics. It's not like this kit is new, just bloody minded manufacturers protecting obsolete IP. Good work Mark. Credit where it's due.
To watch such an engineer as CuriousMarc, with such an equipment and all his experience, struggling to understand and fix a power supply makes me feel so confident, I have months fighting with a TV lamps power supply, thank you CuriousMarc
Have you considered using sockets for the 8 pin DIP IC's? I recently repaired the linear regulator board (card A8) on an HP8720C, it had a 'weak' linear IC where the beta of its output transistor had been reduced over the years. I found that socketing some of the key IC's was handy for troubleshooting and comparing adjacent IC's to each other. Great repair video series, thank you very much for taking on that switching power supply and showing us all how you got it to work again!
...and the next time you have a similar PSU fault, you will remember that it might not behave unless under the correct load. That's why fault chasing like this should be thought of as a learning experience, and not wasted time. A thoroughly enjoyable series. Sending the same wishes back to you and yours at this difficult time.
Back in the 80's we quickly learnt not to try power up an Apple II switchmode power supply without a load. It would immediately "hiccup" sounding as if it was overloaded. Nice diagnosis for the HP.
Thoroughly enjoyable to watch as my technician brain tried to keep up with your thought processes. I know you're very familiar with your test equip, but the way your fingers dance through all the selection keys & softkey menus to view the display you want is just like watching a musician playing an instrument.
Well done. As always, reasoning plays a big part in troubleshooting, repair and reverse engineering hardware. It has served me well for 40 years on the bench. 😃
Nice video series and very instructive, I'm pleased you fixed it, nice to see a piece of kit rescued from oblivion.
I know you realised it wasn't necessary but surely logic would suggest that the only reason to modify the original design would be to mask a fault you'd not yet diagnosed?
As for those in the comments who are hating on the people who suggest changing caps, you've obviously never worked in a commercial repair operation where it becomes obvious very quickly that faulty PSUs with intact fuses can be repaired by cap replacement 30-40% of the time and that it's time/cost efficient to do so, it's not approriate in all cases but it fixes a *lot* of them
I used to fix PSUs and CRTs for a living. The majority of SMPS designs use virtually the same circuit building blocks (although the buck converter block is unusual).
Another cause of failures is the kick start resistor going high. For some reason this tends to result in blown MOSFETs ... the controller chip seems to lock up when it doesn't get enough current from the Kickstarter and the result is always blown FETs.
Great video Marc - that was an epic piece of fault finding and fixing.
You have the patience of a saint. Probably one of the top repairs I have watched.
What a great series of videos! Thank you for sticking with it - most of us need help with switch-mode supplies. I have used a similar photographic technique - or possibly the same one, photographing the top and bottom of the board, flipping the bottom then adding it to the top as a layer and adjusting it's opacity. Very handy for reverse engineering undocumented boards. One key is making sure the top and bottom pictures are both taken at the same distance from the focal plane of the the camera so all traces and components are the same size. A video of your process would be interesting and probably very helpful to others.
Stellar effort! Worst supply I had was my own Sony ProFeel TV monitor (KX-27PS1) that had a weird (Sony Special) self oscillating power supply with a custom resin coated hybrid control board that injected a control signal via an extra winding on the core (ie no opto-isolator). The problem was it would randomly kill the chopper transistor on start up (once a week/month/2 months), this was a known design problem unfortunately. Even stranger part of the design was huge 50w (can't remember exactly) soft start current limiting resistor that was switched out by a relay after 1/2 a second. I ended up fixing it by adding a little more resistance to the soft start resistor to limit inrush current and then worked perfectly for years until the tube's blue gun went weak. Cheers.
I think that the optocoupler may be faulty, in that it's CTR has reduced with age. I recently learned a harsh lesson in that these components don't last forever. I'm told that the LED within the opto suffers from age-related "micro-cracks", thus reduced light output and so reduced CTR. I noticed that your opto is a 1993 vintage part - about the same age as the ones that caused me lots of grief... I think that when you removed and re-fitted the opto, the heat of the soldering process made the opto work again. I'd fit a new one , given the merry dance that I had with (six) aged optos! Many thanks for your interesting videos.
The op-amp was a very good guess. About the effect of the probes, I suspect that probes are adding stray capacitance that helped to stabilize the circuit. I had a similar experience when assembling an audio amplifier that used parallel stages, on a breadboard: all very stable and crisp. On the final PCB, not so, because it went oscillating. Fixed the issue with small caps in parallel with the feedback resistors going from the output to the inverting inputs on both power amplifiers.
Holy crap not an easy fix by any means! Wow. That trick of taking really good quality photos of the board and then mapping it out with photoshop is a brilliant idea. I'll for sure use that trick. I've got an old ATX SMPS that I use just for bench lights and a basic 5v "quick n dirty" supply for things that I took from an old computer tower and "tricked" it with a load to get it to turn all the way on.
Anyhow, I measured it a while back and for some reason, I have +5, -12, +3.3 working just fine, but the +12 I threw on my strip lights is more like 11.7 or so (load or no load). Still runs my lights good enough, but never did fully probe around in there enough to find the source of that problem. Watching this make me wonder, but I fear I may be opening pandora's box after seeing what you contended with haha. Nice work, Marc. Given the equipment yours had to run, you had no choice and quite the challenge to conquer that thing.
My instincts told me that that magical resistance was out of place, and I was right :-) Great video!
What a fantastic series. Thank you for the effort and persistence!
The one "thumbs down" is probably a fan of changing capacitors first.
yuppiehi No, it's HP toadies who don't like #RightToRepair.
Its a Keysight engineer, unhappy that people still love old HP equipment.
You spotted him! Oh, I must be politically correct, Him/Her with their thumb down lol.
Ah yes, the electronic repair equivalent of "when all you have is a hammer, everything looks like a nail". Having said that, I'd still swap the Rifa input caps though ;)
@@BoB4jjjjs congratulations... you win today's political non sequitur award.
It took the same mind that rebuilt the Apollo AGC to fix this power supply. I don't think very many people would have been able to pull this off (at least, without many years studying power circuits). Good job!
You could cover up the pokey bits on those test probes with Kapton tape; that should prevent any more unwanted snap, crackle, and pop!
Fascinating series, a bit above my head but fun to watch You have the patience of a saint!
I put my bet on the PFET in the 300V-to-100V buck converter. You're dealing with a lot of power in this supply, which will stress this FET by quite a bit. Unless that FET turns on and off very quickly (probably doesn't), the average Pd of the FET is quite high. A mistake many make when driving a PFET is putting a little R in series with the gate. This has the effect of slowing down the on/off time of the FET (Miller capacitance integrator), increasing its Pd.
If it shorts out, as it did, then you tripled the input voltage to the 100V DC-DC push-pull converter, causing its outputs to triple in voltage, too. Essentially, everything downstream from the first failed converter was highly overstressed as well, and took out just about everything with it. With 20/20 hindsight from the year 2020, the supply designer should have put in some sort of OVP circuit on that 100V output. But as the expression goes, everyone is brilliant with 20/20 hindsight.
Very impressive reverse engineering, Marc. I enjoyed your debug thought process and various workarounds.
I just rebuilt a power supply for a crt monitor, love seeing this series pop up just as I wrapped up.
Nice that you got it working, that certainly was a journey.
Very clever chap you are ,the switch mode supply put up a big fight but you Conquered it ,Well done .
A colleague and I tackled the switching power supply inside an amateur radio amplifier and that was 48v @ 48amps. The switching circuit was driven by a MA3830 multi regulator but had issues with the control circuit that ultimately led back to the power factor correction IC. The circuit would break into oscillation and to tame it he loaded the switch on and placed a constant 1 amp load on the 48v circuit. Without it the maximum the MA3830 could take was 380v and we already had 370v and coming close to the limit. As this then fed 450v capacitors with (and where Yaesu confused us) with 380v and -380v which is a potential of 760v, however it was just their way of saying 380v and 0v. After quite a few component changes we finally have 48v@48amp of very highly filtered DC from the Yaesu VP1000 power supply (25kg in weight too). Without videos to see the startup loop we would have been rather lost but the complex PFC and oscillation and the MA3830 having staggered pins from left and right in different packages really confused us too. Thank you for a really great video it was enjoyable from part 1 to part 4 and very honest. Kudos
Congrats on your repair, and thanks for recounting your adventure!
I'm a bit behind on my viewing so I only just got round to watching parts 2, 3 and 4 - brilliant bit of fault diagnosing, great fun to watch - love the rant at the beginning of part two!!!!! I love the fact that you actually over fixed it and had to revert back to the earlier fix. Amazing set of videos, great to watch, cheers Marc.
4:14 when he said Hunky Dory, I expected him to say "Winner winner chicken dinner" next :-)
Dave videos definitely taught me a few things!
Fan spin! :)
@@YCbCr ppbus
@@YCbCr Was waiting for that! Shoutouts to Louis! :)
@@CuriousMarc Your optoisolator LED+transistor gain may have gone out of original design assumed spec. When manufactured the LEDs and transistors are individual die and binned by LED emission/current (which drops over age), and similar optocoupler transistor binned by photo-gain (also changes with age and accumulated history of stress from temperature, collector current, Vce). Dealt with this many times before with with suppliers changing optocoupler die specs (manufacturers sell out HP-> Motorola->LiteOn->DiodesInc-> etc and source and bin die differently) and PSU builders substituting optocoupler versions (suppliers bought out, min gain specs get sloppy with replaced LED and transistor die, etc, and suddenly a batch of new PSUs has different load regulation characteristics). Symptoms are usually out-of control switcher feedback loops under transient or at steady low or high currents.
I'd suggest Checking yours with the whole PSU under repetitive pulsed transient loading, say with constant_I of 0.5A + pulsed_I of say 1A, and look closely at the feedback via the optocoupler LED and transistor currents.
I suspect that as you found there's several feedback loops summing via that resistor network. A steady (low frequency) state current feedback loop, and a dynamic loop (via the optocoupler responding switcher cycle by cycle). Your patch explained here may fix the steady state condition, but probably doesn't fix the dynamic/transient load response. Look up the original optocoupler gain spec (LED current to transistor current gain), and consider replacing it with a fresh one with at least the same gain (and suitable Vce and watch for LED die Vf and reverse breakdown if the LED die type has changed from an old GaP to AlInGaP, etc). More optocoupler gain isn't usually a problem since the LM311 should give you a square -wave drive in, but do watch where the 311's output transsitor C and E are wired and how many volts (or reverse bias) can get sent to the optocoupler LED. There may be option to push more current though the optocoupler LED and pick up some gain (but look at the datasheets, binning, and don't assume anything from the optocoupler die supplie - Perhaps stick it on that beautiful HP curve tracer :-)
p.s. I love that you're doing these restorations of wonderful instruments
This was a master class in SPS. Epic ! And thanks for Electroboom effect .
Great work Marc. During my many years as an electronics tech, everyone hated switched modes, except the design engineers and the production managers. I really like HP's gear but their service stinks. Recently tried to download the bios for a 10 year old server. It was right there but no, you can't have it without an active service contract.
One of my livings was running an in-house test equipment REPAIR lab with Tek, HP/Agilent/Keysight, Fluke, Sencore and other respected industrial brands of equipment. They all provided extensive detailed manuals and theory of operation.
(As did Heathkit for hobbyists in their good years).
I am saddened to learn that even Keysight has gone the way of planned appleescence. EVIL beancounter cancer spreads. No used market for keeping a pool of budding engineers and technicians learning.
Join or make a right to repair group in your state.
best youtube content i've seen in a decade of youtube..
Of all of the vintage equipment you could collect, test gear is the best to choose.... you never know when you'll need 4 bench power supplies AND a function generator.
I was working on a defective inverter board from my airco.
Its much much simpler but i suspect a problem with the switchmode part.
This video motivated to push on!
Awesome video. Nice job and way to hang in there. I could not have made it that far!
Just blown away. You are a flippin genius!
Learned a new kind of drastic event: The ElectroBoom! Nice to meet this devastation guy.
You are probably the only person on this planet that can repair these PS from HELL !!!TNX 4 another great video !!!
Congratulations on fixing it, it was probably a worth while experience in the amount of experience you gained. The proper loading of a SMPS has caught me off guard too and I only got the correct voltages when properly loading it around the current draw for it's intended use. Great video's I enjoyed it.
Bill Hewlett & David Packard would have been proud to see you persist and get this fixed. Two kinds of repairs that I hate are those without schematics and those with feedback loops. Reverse engineering this was a HUGE task, but I was expecting you to break the feedback loop somewhere and insert your own control signal, but with more than 1 loop, I don't know if that could have worked. Yes, it was probably the jFET opamp. Nice work, Marc! ;-)
This series was fun, as usual your channel is just at the edge of my knowledge. It's nice to have my brain pushed beyond swapping caps and have to look up a thing or two.
Sir, Thanks a lot to have shared this series of video ... whatched alll from 1 to 4 straight. it helped me a TONS to think better were to look.
Again.
THANKS!
I don’t know much about what you are doing but you do a great job explaining and the video is great.
What a well written thriller with cliffhangers and all. I learned a lot Marc, thanks for sharing your epic battle with us!
I must admit I was cringing the whole time while you were testing/debugging with the supply unloaded. Somehow I knew that was going to bite you. 😋
Cheers! 🍻
Phew, you had me worried for a minute...great job, you're eligible for a Signal Path fix award for sure!
I've thoroughly enjoyed the repair video series for this PSU, thank you!
Great video! I have a similar power supply from an HP spectrum analyser 8563A that has an issue not too dissimilar to this. Fortunatly there is a schematic. I found that most of the parts are badged with HP part numbers which makes it more problematic trying to find the actual device number.
Very cool to see your troubleshooting process and learning about these power supplies
I have also wasted time repairing a SMPSU by not having enough load on it to start up. It basically throttled back so far it didn't generate enough voltage on the auxiliary winding that powered the control chip, so it never completed the boot sequence.
Wow, this was very interesting and a nice look into the physics of switching power supplies. Did you show this to Master Ken? I bet he would like the complexity of this supply.
Fantastic,its been so educational and entertaining hearing your thought processes all the way through.
A large portion of fault finding is about confusion!! if you're not comfortable with that you wont fix things,as faults aren't going to make themselves obvious,i know this from personal history.
I watched episodes two and three several times,to try to understand what might be happening.
After looking at them several times i thought two things:-
(1)what value is Marc setting on his electronic load?
I had no idea what load the power supply was expecting,and wondered if there was any indication on the case,of current and wattage so that you could set a ball park value on your electronic load setting,
If no indication was given,i thought you should set various values,and slowly increase load,whilst watching regulation behaviour.
(2)My other thought was, that there must be something flaky happening in the feedback path,and so the mad cappers maybe onto something after all!!!
I was too chicken to send my first suggestion,after all Marc has repaired more SMPSU's than i've had hot dinners,just let him think in peace!!
The Alto Power supply repair was hilarious....these power supplies are evil!
The days of simple linear power supplies are gone.
Terrific videos Marc,thank you for sharing,you are stimulating the noggin..
@5:48 Oh man! I have that exact same "Digi Designer"! Never seen someone else with one :) They are handy for quick little tests like that. The built in power supply and square wave generator is great.
Yes it's so nice! And look at that other monster one I recently acquired I repaired, from the same company: th-cam.com/video/enMAp99udqw/w-d-xo.html .
i have loved this series. we fixed soooo many power supplies for old but otherwise excellent equipment in our low temperature (micro K) physics lab.
Regarding the probes, indeed sometimes you need extra high quality ones with very low capacitance or they will increase the capacitance of the traces so that it will change the behavior of the device. Had similar issue when chasing the I2C issues and noise on the line - if the standard probes were attached the I2C line behavior changed quite a bit. It was required to use special probes to see exactly whats happening on the line.
Removing input and output caps and limiting the amps with a light bulb in series should work too.
A IR camera is really helpful for finding faulty components too.
How could someone put a thumbs down. This has been one of the most enthralling electronic adventures I've seen. Kudo's to the solution! Be safe.
Congrats on a wonderful journey thru power supply repairs.
Loved your whole serie on the fixing of the SPS. learned a little trick of using photo to trace the lines with photo software very good. Will keep it for futur debugging job
I never doubted you Marc. I knew you would fix it! That was a pain though. Good stuff
Hope you are safe and healthy too Marc. Enjoyed the ride through the PSU, It was like me being a fly on the probe :)
And now you know why technicians have so much stuff on their benches. IT'S ALL USEFUL! "I'LL NEED IT ONE DAY!" Jimmy Diresta would be proud ("Better to have it and not need it, than to need it and not have it" - he's quoting someone else, but he lives by that idiom).
Great that you got it working! Great lessons here to. Fun to watch.
Very interesting to see how the little resistor changes the regulation range :)
Great job, new you would find it. My guess is the PS was not an HP design but contracted out. All the HP stuff I have ever looked at for the most part follow the kiss principal, clearly it was not followed in this case.
Thinking of all the info needed to have at hand in operating this absolutely fabulous collection of vintage and up-to-date electronic instruments gives me a headache ...
Superb series, thank you for sharing them with us. 👍
Argh, those damn probes misbehaving again ?
Ground them, that'll teach team !
Hahaha! I must reuse that joke in an episode!
Wow what a marathon. Glad you got the beast tamed...
I have seen several switchers be unhappy with low current loads. A few I got surplus had a minimum load listed shown on the label with the other specs. Wish I had a tracking genny that went that high in freq. My IFR only goes to 1900MHz.
This is a great series, and gives me hope that eventually I will feel confident enough to try to repair the broken PSU in my IBM 5150. I will not dare touch it until I feel I at least know the basics and how to be safe. Getting there! Like you, I'd rather not simply recap and pray; I am a huge fan of trying to understand the problem. Especially as I still have such a lot to learn and am not working to time constraints (hobby, for now). :)
Nice work tracking that one down.
Thank you for that adventure. I learned alot, Including to test opamps to look for the voltage between + & -
To me it seemed a little bit like the optocoupler was always bad since things changed after resoldering and you never messed with it before. Assuming a single component failure, maybe this caused the DC voltage to go high and start blowing stuff up? Assuming more than one failure, surely the opamps were not good
Very interesting! I was almost blaming the project for marginal design in the control loop
17:17 At least have some respect for the dead, and cover them with a sheet or something. LOL. Good show Marc.
I wonder if those yellow mains filter caps on the left are the famous explodey rifa types or if these are new enough to be better?
Well done sir, I think I would have gave up on the second video. Mind you, you have all the equipment there to fix most things and also the knowledge to repair it. Very good interesting video, yes it looks like it was designed for a full load all the time. For me it is over complicated, over designed no doubt over expansive as well.
Fantastic conclusion! I try to never assume a test setup is applicable for the unit under test. If it doesn't work out of a device's normal environment, what did I do wrong in setup?
God job! repairing is always worth it. Especially your own instruments.
I LOVE your "digi designer" ..... great little chip tester!
Breadboards are good for testing and for educational purposes.
Great stuff! I was wondering whether a thermal image analysis would have shed any 'light' on the situation?
Not likely, since there is no known normal heat map, and the damaged components blow up outright
man you're dedicated, love your videos, new member in your channel BTW and I love it
"Electroboom moment". All credits for you for inventing this term. Those power contacts on the table I have never seen them before. Which country are they from?
@16:31 - and this is what happens when you spend this long trying to fix a switch mode PSU without any documentation.
Hopefully Marc will recover. :D
Cheers on getting the thing going again.
C'est dingue! Chapeau Marc!
Well done Marc
Excellent work and patience 👌
But but but you didn't replace any capacitors. ;-) hehe. Loved the dip in to switching power supply theory. Awesome stuff!