35:10 "I'm actually shocked!" may not be the best phrase when working around a sketchy power supply heheh! Amazing work in any case, though! I love to see the attempt of saving the original power supply nonetheless.
I'm really glad to see that you at least tried to restore the original power supply. Particularly for a device like this that's so rare, it really is good to try to preserve as much of it as possible in as close condition to the original form as you can. I'm pretty sure that what happened with that charred corner of the board is just that the capacitor blew out, which caused its electrolyte to vaporize and leave at high pressure out the bottom. Capacitor electrolytes can be highly flammable, so the escaping jet stream probably arced and caught on fire outside the capacitor, so you then had essentially a mini blow torch of high-pressure flame going through any openings on the board to the other side, and then out, charring the back side of the board as it spread out and escaped. Also, after "reforming" a capacitor, you really should hook it up to an LCR meter to verify what its actual capacitance and series resistance are, and make sure they're not too far out of spec. Just because it isn't actually shorted doesn't mean that it hasn't still lost a lot of its capacity or developed significant extra resistance in the process (and may not function well in the intended circuit as a result). You also really should test the voltage regulator with some load on it before assuming it's good (for a linear regulator, a no-load test is perfectly OK to do, and a good first start, but really still doesn't tell you whether it will actually continue to regulate properly under normal operating conditions). I personally keep a variety of low-value, high-power resistors for this sort of thing (in this case, putting a 10 ohm 100-watt resistor across the outputs would be a good test, IMHO (maybe 60-ish ohm for the 15V outputs). The reason why horizontal and vertical deflection have independent regulators is almost certainly to prevent keystoning or barrel distortion. Otherwise the changing load of the vertical drive circuit can affect the voltage supplied to the horizontal drive circuit, which will result in a picture that's wider at one part of the screen than at others.
Nice work, as always! Just a tip on reforming - because you had the current limit set to a safe 5mA, you could then set the voltage to the maximum, 30VDC and let the supply automatically ramp the voltage up as the cap slowly charges. Once it reaches 30V, the supply will automatically switch back to constant voltage mode to finish the reforming at max DC. If you want to set the ramp speed, you can adjust the current. The general formula is: i * t = C * V, where "i" is current, "t" is seconds, "C" is Farads, and "V" is voltage. Solving for t in this case, t = C * V / i, or 18mF * 30V / 5mA = 108 seconds. That is for an Ideal cap, of course. Leakage or reforming will take longer, or for ever!
Glad you got the original PSU going. Surprised the board took that much damage under the cap and it didn't blow out a regulator, diode, or smoke the transformer windings.
Well done! Glad to see you got the original PSU working. It would have almost been a shame to have to replace it with a SMPS. When you charged the "new" capacitor and it took so long to discharge (~28:25) , maybe that's why they had the bleed resistor on the old one, not for safety, but to make sure the PSU actually stopped powering the motherboard once it was shut off.
I really, really enjoy your content. Your level of dedication in your repairs, showing in detail how everything works, is something I truly value. Keep it going!
I'm glad the original PSU is operational and I was quite surprised that the carbon mess wasn't through the board. As I said in a comment on your last video, I had seen worse damage caused by actual shorts and burn ups. Those voltage regulators and heat sinks can be put together incorrectly. Back when I was repairing linear power supplies, someone in manufacturing forced the two together on a bunch of power supplies. When I powered up the first one, there was a dead short across the power and ground that not only blew the regulators off the board but also the electrolytic capacitors as well! As you can imagine, I was quite gun shy about powering up the power supplies afterwards and my coworkers used to play tricks on me when I was assigned them for repairs.
Yep... for example the 78xx (positive) and 79xx (negative), at least certain casings, are different in that for the 78xx the reference voltage is on the heat mount, but 79xx has the regulated voltage on it... or maybe input, would have to check, because it's been years I fooled around with 79xx... but you absolutely can't slap them on the same heatsink without insulation on at least one.
@@jussikuusela7345 It was pretty "shocking" with sparks and an explosion! The people in assembly actually put them on the boards backwards through the heatsinks which were touching the metal legs. No one could tell until the units were powered up and once the first one blew up, out came the DVM and we tested the remaining ones via the meter and sent them all back to assembly for repair. I learned a ton about computers, CRTs and peripherals at this place. The company made Z80 based video terminals, CP/M computers and a portable IBM compatible until they purchased another company that made 8085-based terminals and systems that supported Hawk, Phoenix, and Finch drives, floppy disks, and proprietary I/O cards for various companies. All of this is sadly gone and when I watch Adrian's repairs, I think back to my tech days back in the 80s.
Again: flashover like you see there can happen at any voltage as long as the required current is available to make the havoc you see there. Even 0,1V could do that with a big enough cap or battery. :) If you don’t believe me go find a big fat wrench in your garage, open the hood of your car and drop it onto the plus and minus on your cars battery. It will go up in smoke along with your car. The wrench will go flying or if it get welded to the posts it will vaporize. The lower the voltage the more amps you need but with a capacitor that size on the board the energy is there to make that board do way more than that little flash you see there. There is a reason we say have respect for big caps. It’s not just the HV on a tv/monitor that can get you.
How about an extras video where you pull apart that bad cap? The internal failure might be interesting to look at. Just seeing the internal structure of an ancient cap would be interesting on its own
And it's the perfect size for it! It'll be like those giant-sized models to make details easier to see but in real life! (I actually have no idea if huge caps are just scaled-up versions of smaller ones or not.)
I am so glad you decided to try and fix the old linear power supply. I hope it all can be fixed as it stands. I know there is no hope for that crt, but this is a great restoration video. Thanks.
Here I am, a lot younger than that terminal and had zero experience with one of them, watching your videos and just get amazed by your genius, dedication, love of the craft, and a masterfully presented narration. Great work Adrian! I'm in awe.
I highly recommend getting yourself some baby wipes for your hands near the bench. They're gentle but they will take Gunk like that off your hands pretty easily!
My Testofon will tell you the carbon is problematic at any voltage. Well it depends on the circuit. But if I can measure leakage through the PCB at 5V, then it can cause issues.
Purple center tapped winding uses a full wave rectifier (NOT BRIDGE) with two sets of diodes to provide positive and negative outputs. Non-center tapped windings use a bridge rectifier to provide single polarity output. Yes, a Bridge rectifier does give full wave output, but it is NOT the usual full wave circuit, it has double the diode voltage drop as there are two diodes in series.
Please don't write off the tube, test it and if it has usable emissions, go ahead with the cataract removal. With this level of deterioration, you probably need minimal to no heat to remove the glass.
Even if it’s not worth saving, use the tube as practice for cataract removal, especially if you need to figure out a technique for winter time procedure
I really enjoyed the explanation of how the circuit worked and testing methodology. Watching this channel and a few others has inspired me to repair my own electronics. For instance, I had a recent failure of one my all in one solar charge controller/inverters. The solar input was a dead short. After checking around the circuit, I found the large input capacitor had failed in a dead short. The part only costs about $8 and a new unit costs $900. This the second unit I have had fail this way. It makes me wonder if putting 440V through a 500V rated capacitor was to blame or if the capacitor was just substandard. Thanks for the great videos and the inspiration.
Mmmm, krispy large electrolytic :D - Good to see that most of the electronics looks like they're broadly functional. The all discrete logic board for the terminal controller is comically large - It is getting up there with the size of the main board for that Plexus mini computer you have! Festive greetings to you and yours, @Adrian. 🍻
Yes, the cap was definitely shorted. Carbonized board certainly can be conductive too - seen it several times; and pretty low resistance too (when burned completely through, as this one appears.) Carbon = conductive. Since it's charred on both sides, the prudent thing to do is to dremel all of the carbon out of the board. Otherwise, the risk of board shorting will remain... when the board heats up enough, or in high humidity, or after some vibration, or a change in the phase of the moon...
@ a carbonised PCB will be a leakage path, not a hard short, and they can cause further carbonisation and damage. Have you heard of carbon resistors? That’s right, carbon, the same stuff the PCB has turned into.
At the step of being ready to power up the electronics I really recommend putting a light bulb in series of the mains. If it light up you know you have a short and you limit the damage that can be caused if something goes wrong. Think of it as a constant current limit. It can’t draw more than the bulb would allow then and the voltage would drop on the computer - thus limit the risk of catastrophic damage. A 40watt bulb would be plenty to fire up the motherboard without the CRT.
@@Kruton1122 it translates the title and/or the description of the video to the user's app language. it's annoying to so many people who can read and understand english. edit: the translations are usually controlled by the channels themselves. only they can truly turn it on or off.
Soroc: manufacturer of terminals with a nice "70s space-age" aesthetic. Ciroc: fancy vodka. Sarek: Spock's father. "Que Soroc Soroc, whatever will be, will be..." I'm happy to see the "juicy" cap didn't appear to cause any further damage when it released the magic smoke... I guess we'll see in Part 3, but things are definitely looking good!
I always envy you for that nice Plexus system in the background. Back in the early 80's, I always wanted such a UNIX supermicro. Actually had to wait for IBM AT clones, to get my first personal UNIX system :)
At the recording studio I worked at in the 90's, we purchased a brand new Revox PR-99 open reel tape machine that was dead in the box. Since we were based in Nashville, Studer had a factory parts and service center locally at the time and we took the tape machine in for repair. They fixed it for us in a day. Turns out one of the AC electrolytic filter caps shorted on the power supply board and blew the power supply fuse, saving the tape machine from further damage. So even brand new caps can short and fail.
Would be really tempted to paint on some solder mask between the traces on the bottom of the board. At the low voltages the air gap is probably fine But all that solder with such narrow gaps has me concerned that shorts could happen
The guys who designed the terminal were sitting around, drinking beer, and trying to come up with a name and a logo. They were drinking Coors. Soroc is an anagram thereof. And the logo is the top view of an opened beer can.
11:52 because the capacitor was probably charging up, especially with that large size it was /hungry/ (unless it's bad, of course) [posting before watching further]
Nice work. Glad to see that you were able to save the original PSU. How about an autopsy of the failed capacitor? Maybe we'll find out what exactly is causing the short.
When you're testing the +5 using the bench supply to feed the filter cap there is no load on the circuit. With load the regulated voltage may start to drop which is expected. This is why you often see linear supplies ser at 5.t or so volts. Under load it will drop towards 5V.
Εξαιρετική δουλειά ως συνήθως, αυτός ο τεράστιος πυκνωτής θα εκανε μεγάλο μπαμ αν έσκαγε αλλά μάλλον εβγαλε τα υγρά του στο περιβάλλον κ έκανε τη ζημιά αυτή. Ο καινούργιος μπλέ που έβαλες φαίνεται κ να είναι σωστό σε λειτουργία κ είναι πιο όμορφος απ τον παλιό ίσως να έφτιαχνες μια μικρή βάση εκεί για να κάθεται όμορφα στην πλακέτα? Περιμένω με αγωνία το επόμενο μέρος της σειράς, Χαιρετίσματα απ την Ελλάδα!
Wouldn't be a good idea to feed the sync signals and the video to a ttl monitor or one of yours capture thingies to see what's on the screen? This shold be a quick check. Of course replacing crt and making it work is a good plan too and also keeps the suspense... :) Cheers! Happy Holidays.
Just FYI, Laowa makes some really nice 7.5 and 10mm manual focus lenses for the micro four thirds system that are a bit less expensive than the Panasonic ones. TTArtisan 10mm lens could also work while being really cheap.
2:18 I would guess a paper clip, lost washer or staple having caused a massive short. And - unlike to more modern caps - these are not short-circuit proof. If they are loaded up and a direct short is applied the internal current rush can damage the foils ... which leads to disasterous failures. More modern caps designed for switchmode supplies can withstand way higher charge and discharge currents than these antiquities ... 🙂
The implosion protector glass on the front of that old CRT would actually come off pretty easily if you put it in front of a space heater set to high. All you'd need then would be an E string from an old guitar between two bars that you'd use as handles turning the string into a saw. You might not even need the heat considering how degraded the adhesive is in it's current state.
I have an old VGA lcd pc monitor i suspect needs some new capacitors. When it has been off for some hours, it shows RGBW bars trying to start, then it shows the logo trying to start, but when it finally turns on, it works perfectly. I don't have the equipment or know how to fix it, so I bought a new one.
They're the first soldiers to die out in any electronic products after the battery of course. They're very similar to a battery. After 20 years old, sitting in a drawer unused they still can't work like new fresh ones. Just like trying to charge dead battery, the ancient or tired from use Electrolytic capacitor (specifically) refuses to recharge anymore and just heats up and can cause other components to burn up. They operate by a wet chemical reaction. Those chemicals age out and become no good anymore just like old beer. Not poison but not good drinking anymore.
35:50 - you said center-tapped, but that is probably wound in a bifilar manner, with the “low end” of one winding connected to the “high end” of the other. Winding it in this manner ensures that each winding has equal turns to its counterpart, thus essentially equal voltage and essentially equal DC resistance.
I worked at Acme Electric in Cuba, NY before the CEO took the company private and destroyed company. Shortly after the Cuba division was sold off and then closed. Cuba was a great place to work.
Another option instead of using another switch mode power supply if you did need to replace the original PSU would be to just use a small boost regulator on the 12V rail of the modern power supply (assuming the current isn’t too high).
I wonder if given that the glue goo seems to be soluble in IPA if you could soak the CRT face down in a shallow bath of IPA and then get that front glass separated.
Talking about power supplies, I was looking for something that would work well off a 2s li-ion battery and/or a 12v wall power supply and came across the MEZD41502A-C. It’s a little 2A boost converter that will run nicely off 5ish all the way to 12v. Unfortunately, Monolithic seems to have decided not to produce anymore of the pre-built module, though they publish a reference circuit and seem to want to keep the 12v version and base IC around.
Hi Adrian! Regarding your concerns at the beginning of the video with respect to the mains power transformer not having all it's outputs loaded. Well, good mains power transformers do not work like that! Meaning, each output winding has it's own turn ratio with respect to the primary winding, and that is the only thing that sets ( or should be ) each output voltage. If loading one winding, significantly reduces voltages on other windings, then that power transformer is poorly designed, because that can only happen when the primary winding is underrated ( not even high leakage inductance could do it, because that would further isolate the loaded winding ), meaning it's copper wire is too thin, and looses too much voltage under load. A good mains power transformer should keep it's output voltages fairly constant no matter what winding is loaded, and by how much ( within specs, of course ).
I wanted to comment on the last video how it looks like that cap has started leaking and caught on fire while the machine was running, as I have an amplifier in my basement that had the same problem - the owner used it for PA of a soccer game and the match was just over and he wanted to pack in and it burst into flames. But those caps were running at 70V so I too didn't expect that at 9ish Volts. (and even though that happened in 1990, there was still some cap juice left)
I have witnessed when electrolytic capacitors leak, that conductive electrolyte can short out systems and cause a lot of problems. My bet is that electrolytic leaked onto the board and cause a short circuit that then burned the PCB. If that is just a two layer (top/bottom) PCB you can cut or grind the PCB material away and rebuild it with off the shelf PCB repair stuff (like epoxy or some such), and then run copper tape "traces" to fix the PCB permanently. Had to learn how to do this at a previous job. Because we supported equipment that you may or may not be able to get replacement parts in a timely fashion. So we had to learn how to rebuild a PCB.
4:37 "It's pretty modern. I think it's from 1999" 1999 was a quarter of a century ago. However, I really think 1999 technology is more similar to today technology than either is to 1979 technology, so in a way, you're kinda right with the "modern" bit.
Soroc IQ120 is an interesting beast, with some of the functionality driven by EPROM based state machines, if I recall correctly. I worked on a few in the late 70s. The 7912 regulator is most likely for the negative rail on the RS232 drivers (MC1488...?), and the minus 5v from the zener would perhaps simply be a negative bias for a PMOS ROM or similar, so not that critical. (I've also got the manual in a pdf somewhere, but this is just from memory.)
I’ve seen the little caps in electronics pop violently. Not sure I would put my face that close to one that big. I realize it’s a very controlled power which is a much safer and ideal situation.
Linear power supplies are dead simple, so I would have begun with the transformer, and if it checked out, I’d doubled-down on repairing it as any of the components are simple and cheap. I would have liked to have seen a multi-megohm measurement between the primary and secondary windings since you considered the transformer was suspect.
What Brainiac would use locktite on an electrical connection? You should only use that on a mechanical connection, for anything electrical just use lock washers!!!!
I wondered about that. Screws in aluminium capacitors sometimes can become seized due to corrosion from the screw an capacitor thread being of dissimilar metals. I was thinking it might just be a residue from such corrosion.
It is a bit fun how things have developed. Here we see a computer that uses a simple 240 ohm 1 W resistor (R1 at 38:10) and a zener diode to provide 12 volt to the whole system, since it sees practically no meaningful load. Meanwhile in modern computers, 12 volt is more or less the only source of power for everything.
Great, I really wanted to know if that capacitor was blown. So it was. I've seen smaller ones blowing holes in PCB's but they ran at higher volts inside an old switching PSU. Those where only 10 uF 450Volt capacitors. Imagine what a 15000 uF capacitor can do to your PCB.
I'll get no price for this, but a shorted cap was my immediate thought when I saw the burned PCB. I can't see anything else causing this. Congrats on getting it back though. Did you replace the thermal compound on the linear regulator? Looking forward to part 3.
I wonder if the terminal got plugged in for testing decades later without letting that big capacitor reform correctly and the heat from the sudden current draw shorted it out through a c.ascade of fusing plates? 🤔
Theres some great PCB artists around.. maybe someone could recreate the PCB from scans, etc. then it would be just a matter of transferring over as many of the intact and working over from the original.
Wow, that level of board damage reminds me of the testing reported by Sandia Labs in their TH-cam series "Always Never" about the safety and reliability of the systems controlling nuclear weapons. One of their discoveries was that electronics can do very strange and unexpected things when exposed to fire and other adverse environments. I wonder if that board is now electrically conductive? 🤔🤷♂
35:10 "I'm actually shocked!" may not be the best phrase when working around a sketchy power supply heheh! Amazing work in any case, though! I love to see the attempt of saving the original power supply nonetheless.
Safer to remove the insides from the tall cap and put a new cap of same value inside the case so it still looks genuine.
LOL I thought the same thing.
I'm really glad to see that you at least tried to restore the original power supply. Particularly for a device like this that's so rare, it really is good to try to preserve as much of it as possible in as close condition to the original form as you can.
I'm pretty sure that what happened with that charred corner of the board is just that the capacitor blew out, which caused its electrolyte to vaporize and leave at high pressure out the bottom. Capacitor electrolytes can be highly flammable, so the escaping jet stream probably arced and caught on fire outside the capacitor, so you then had essentially a mini blow torch of high-pressure flame going through any openings on the board to the other side, and then out, charring the back side of the board as it spread out and escaped.
Also, after "reforming" a capacitor, you really should hook it up to an LCR meter to verify what its actual capacitance and series resistance are, and make sure they're not too far out of spec. Just because it isn't actually shorted doesn't mean that it hasn't still lost a lot of its capacity or developed significant extra resistance in the process (and may not function well in the intended circuit as a result). You also really should test the voltage regulator with some load on it before assuming it's good (for a linear regulator, a no-load test is perfectly OK to do, and a good first start, but really still doesn't tell you whether it will actually continue to regulate properly under normal operating conditions). I personally keep a variety of low-value, high-power resistors for this sort of thing (in this case, putting a 10 ohm 100-watt resistor across the outputs would be a good test, IMHO (maybe 60-ish ohm for the 15V outputs).
The reason why horizontal and vertical deflection have independent regulators is almost certainly to prevent keystoning or barrel distortion. Otherwise the changing load of the vertical drive circuit can affect the voltage supplied to the horizontal drive circuit, which will result in a picture that's wider at one part of the screen than at others.
Thank You For the information! I appreciate your time and effort! I hope you are having a great day or night my brother!
"see the exploded drawing" ... how prophetic
Nice work, as always! Just a tip on reforming - because you had the current limit set to a safe 5mA, you could then set the voltage to the maximum, 30VDC and let the supply automatically ramp the voltage up as the cap slowly charges. Once it reaches 30V, the supply will automatically switch back to constant voltage mode to finish the reforming at max DC.
If you want to set the ramp speed, you can adjust the current. The general formula is:
i * t = C * V, where "i" is current, "t" is seconds, "C" is Farads, and "V" is voltage.
Solving for t in this case, t = C * V / i, or 18mF * 30V / 5mA = 108 seconds. That is for an Ideal cap, of course. Leakage or reforming will take longer, or for ever!
an 'easier' way is to reform from a fixed voltage supply at working volts, but limit current using a filament bulb...
Glad you got the original PSU going. Surprised the board took that much damage under the cap and it didn't blow out a regulator, diode, or smoke the transformer windings.
Well done! Glad to see you got the original PSU working. It would have almost been a shame to have to replace it with a SMPS. When you charged the "new" capacitor and it took so long to discharge (~28:25) , maybe that's why they had the bleed resistor on the old one, not for safety, but to make sure the PSU actually stopped powering the motherboard once it was shut off.
I really, really enjoy your content. Your level of dedication in your repairs, showing in detail how everything works, is something I truly value. Keep it going!
I'm glad the original PSU is operational and I was quite surprised that the carbon mess wasn't through the board. As I said in a comment on your last video, I had seen worse damage caused by actual shorts and burn ups.
Those voltage regulators and heat sinks can be put together incorrectly. Back when I was repairing linear power supplies, someone in manufacturing forced the two together on a bunch of power supplies. When I powered up the first one, there was a dead short across the power and ground that not only blew the regulators off the board but also the electrolytic capacitors as well! As you can imagine, I was quite gun shy about powering up the power supplies afterwards and my coworkers used to play tricks on me when I was assigned them for repairs.
Yep... for example the 78xx (positive) and 79xx (negative), at least certain casings, are different in that for the 78xx the reference voltage is on the heat mount, but 79xx has the regulated voltage on it... or maybe input, would have to check, because it's been years I fooled around with 79xx... but you absolutely can't slap them on the same heatsink without insulation on at least one.
@@jussikuusela7345 It was pretty "shocking" with sparks and an explosion!
The people in assembly actually put them on the boards backwards through the heatsinks which were touching the metal legs. No one could tell until the units were powered up and once the first one blew up, out came the DVM and we tested the remaining ones via the meter and sent them all back to assembly for repair.
I learned a ton about computers, CRTs and peripherals at this place. The company made Z80 based video terminals, CP/M computers and a portable IBM compatible until they purchased another company that made 8085-based terminals and systems that supported Hawk, Phoenix, and Finch drives, floppy disks, and proprietary I/O cards for various companies.
All of this is sadly gone and when I watch Adrian's repairs, I think back to my tech days back in the 80s.
Again: flashover like you see there can happen at any voltage as long as the required current is available to make the havoc you see there. Even 0,1V could do that with a big enough cap or battery. :) If you don’t believe me go find a big fat wrench in your garage, open the hood of your car and drop it onto the plus and minus on your cars battery. It will go up in smoke along with your car. The wrench will go flying or if it get welded to the posts it will vaporize. The lower the voltage the more amps you need but with a capacitor that size on the board the energy is there to make that board do way more than that little flash you see there. There is a reason we say have respect for big caps. It’s not just the HV on a tv/monitor that can get you.
Excellent! so much more interesting then just popping in a new power supply.
"Absolutely Good Enough" - I'm making a t-shirt.
Also make one that says: What? It just freaking works!
How about an extras video where you pull apart that bad cap? The internal failure might be interesting to look at. Just seeing the internal structure of an ancient cap would be interesting on its own
And it's the perfect size for it! It'll be like those giant-sized models to make details easier to see but in real life! (I actually have no idea if huge caps are just scaled-up versions of smaller ones or not.)
I am so glad you decided to try and fix the old linear power supply. I hope it all can be fixed as it stands. I know there is no hope for that crt, but this is a great restoration video. Thanks.
Here I am, a lot younger than that terminal and had zero experience with one of them, watching your videos and just get amazed by your genius, dedication, love of the craft, and a masterfully presented narration. Great work Adrian! I'm in awe.
I highly recommend getting yourself some baby wipes for your hands near the bench. They're gentle but they will take Gunk like that off your hands pretty easily!
@18:00 you should grind out the PCB where the carbon is still present, it could cause problems later especially if it gets humid.
Only around 15 volts on there - the carbon won't really be a problem
My Testofon will tell you the carbon is problematic at any voltage. Well it depends on the circuit. But if I can measure leakage through the PCB at 5V, then it can cause issues.
@@elektro-peter1954 it in a humid environment is can be a problem even at low voltages.
Purple center tapped winding uses a full wave rectifier (NOT BRIDGE) with two sets of diodes to provide positive and negative outputs. Non-center tapped windings use a bridge rectifier to provide single polarity output. Yes, a Bridge rectifier does give full wave output, but it is NOT the usual full wave circuit, it has double the diode voltage drop as there are two diodes in series.
Please don't write off the tube, test it and if it has usable emissions, go ahead with the cataract removal. With this level of deterioration, you probably need minimal to no heat to remove the glass.
Even if it’s not worth saving, use the tube as practice for cataract removal, especially if you need to figure out a technique for winter time procedure
I really enjoyed the explanation of how the circuit worked and testing methodology. Watching this channel and a few others has inspired me to repair my own electronics. For instance, I had a recent failure of one my all in one solar charge controller/inverters. The solar input was a dead short. After checking around the circuit, I found the large input capacitor had failed in a dead short. The part only costs about $8 and a new unit costs $900. This the second unit I have had fail this way. It makes me wonder if putting 440V through a 500V rated capacitor was to blame or if the capacitor was just substandard.
Thanks for the great videos and the inspiration.
Those MR diodes in the bridge are sort of like fuses, when the get hot the ceramic pill of the diode just falls away from the leads
Those are cool looking diodes
Glad you didn't take the easy way out. Love the power supply repairs. 💪
Have a happy holidays Adrian's Digital Basement
Love the progress!
Excellent progress! I'm looking forward to seeing this thing come to life and show a video display.
(Take some time to enjoy the Holiday Season, man.)
Loved the diagnostic approach.
Fantastic work, i love seeing this sort of work, top marks for saving the old girl, your almost there.
Nice work! Really impressed.
This is what I call a job well done!
Mmmm, krispy large electrolytic :D - Good to see that most of the electronics looks like they're broadly functional. The all discrete logic board for the terminal controller is comically large - It is getting up there with the size of the main board for that Plexus mini computer you have!
Festive greetings to you and yours, @Adrian. 🍻
@9:55 the short is probably from the burnt area, carbonised PCB is conductive.
It was not.
Yes, the cap was definitely shorted. Carbonized board certainly can be conductive too - seen it several times; and pretty low resistance too (when burned completely through, as this one appears.) Carbon = conductive. Since it's charred on both sides, the prudent thing to do is to dremel all of the carbon out of the board. Otherwise, the risk of board shorting will remain... when the board heats up enough, or in high humidity, or after some vibration, or a change in the phase of the moon...
@RabbitHoleLabs not saying it isn't possible, but in this specific case the dead short was from the cap.
@ a carbonised PCB will be a leakage path, not a hard short, and they can cause further carbonisation and damage. Have you heard of carbon resistors? That’s right, carbon, the same stuff the PCB has turned into.
@TheDefpom as I said I'm not at all saying it doesn't happen, it's just that in this case it wasn't the cause of the short.
At the step of being ready to power up the electronics I really recommend putting a light bulb in series of the mains. If it light up you know you have a short and you limit the damage that can be caused if something goes wrong. Think of it as a constant current limit. It can’t draw more than the bulb would allow then and the voltage would drop on the computer - thus limit the risk of catastrophic damage. A 40watt bulb would be plenty to fire up the motherboard without the CRT.
Please, dont let YT autotranslate your titles...
I strongly agree to you. For the time being I changed the app language to English.
What’s it do?
@@Kruton1122 it translates the title and/or the description of the video to the user's app language. it's annoying to so many people who can read and understand english.
edit: the translations are usually controlled by the channels themselves. only they can truly turn it on or off.
What's the point of auto-translating?
@darksidegryphon5393 to reach out other language speakers. simple as that.
Soroc: manufacturer of terminals with a nice "70s space-age" aesthetic.
Ciroc: fancy vodka.
Sarek: Spock's father.
"Que Soroc Soroc, whatever will be, will be..."
I'm happy to see the "juicy" cap didn't appear to cause any further damage when it released the magic smoke... I guess we'll see in Part 3, but things are definitely looking good!
I always envy you for that nice Plexus system in the background. Back in the early 80's, I always wanted such a UNIX supermicro. Actually had to wait for IBM AT clones, to get my first personal UNIX system :)
At the recording studio I worked at in the 90's, we purchased a brand new Revox PR-99 open reel tape machine that was dead in the box. Since we were based in Nashville, Studer had a factory parts and service center locally at the time and we took the tape machine in for repair. They fixed it for us in a day. Turns out one of the AC electrolytic filter caps shorted on the power supply board and blew the power supply fuse, saving the tape machine from further damage. So even brand new caps can short and fail.
Adrian, have a wonderful Christmas and bless you and your family. Hope you'll find some super trooper tech under the tree :))
Excellent troubleshooting video!!
Would be really tempted to paint on some solder mask between the traces on the bottom of the board. At the low voltages the air gap is probably fine But all that solder with such narrow gaps has me concerned that shorts could happen
So excited for the next part!
Brilliant Adrian as usual 😅
Great video! Merry Christmas!
The guys who designed the terminal were sitting around, drinking beer, and trying to come up with a name and a logo.
They were drinking Coors. Soroc is an anagram thereof.
And the logo is the top view of an opened beer can.
That is a classic clifhanger! Can't wait for series finale!
Stealthy display of Rick Hastley in the background. Nice one :)
Looking forward for next part ❤
11:52 because the capacitor was probably charging up, especially with that large size it was /hungry/ (unless it's bad, of course)
[posting before watching further]
Even the good ol’ caps can go BAD! Reminds me of the shirt you wear. Love it!
Great work!
Nice work. Glad to see that you were able to save the original PSU.
How about an autopsy of the failed capacitor? Maybe we'll find out what exactly is causing the short.
Came in later and so great you got the ps working...wooot! 😊
Great video!
When you're testing the +5 using the bench supply to feed the filter cap there is no load on the circuit. With load the regulated voltage may start to drop which is expected. This is why you often see linear supplies ser at 5.t or so volts. Under load it will drop towards 5V.
Εξαιρετική δουλειά ως συνήθως, αυτός ο τεράστιος πυκνωτής θα εκανε μεγάλο μπαμ αν έσκαγε αλλά μάλλον εβγαλε τα υγρά του στο περιβάλλον κ έκανε τη ζημιά αυτή. Ο καινούργιος μπλέ που έβαλες φαίνεται κ να είναι σωστό σε λειτουργία κ είναι πιο όμορφος απ τον παλιό ίσως να έφτιαχνες μια μικρή βάση εκεί για να κάθεται όμορφα στην πλακέτα?
Περιμένω με αγωνία το επόμενο μέρος της σειράς, Χαιρετίσματα απ την Ελλάδα!
It's all Greek to me.
This is a great series, really enjoying it!
That large cap reminds me of the single cap in an Atlas Desktop power supply. It was huge.
Wouldn't be a good idea to feed the sync signals and the video to a ttl monitor or one of yours capture thingies to see what's on the screen? This shold be a quick check. Of course replacing crt and making it work is a good plan too and also keeps the suspense... :) Cheers! Happy Holidays.
Como me encanta este canal
There is a PACE video from the 70/80's that shows rebuilding a PCB with heavy damage. It might be a good idea to review that.
th-cam.com/video/HKX-GBe_lUI/w-d-xo.html Interesting...
Just FYI, Laowa makes some really nice 7.5 and 10mm manual focus lenses for the micro four thirds system that are a bit less expensive than the Panasonic ones. TTArtisan 10mm lens could also work while being really cheap.
2:18 I would guess a paper clip, lost washer or staple having caused a massive short.
And - unlike to more modern caps - these are not short-circuit proof. If they are loaded up and a direct short is applied the internal current rush can damage the foils ... which leads to disasterous failures. More modern caps designed for switchmode supplies can withstand way higher charge and discharge currents than these antiquities ... 🙂
The implosion protector glass on the front of that old CRT would actually come off pretty easily if you put it in front of a space heater set to high. All you'd need then would be an E string from an old guitar between two bars that you'd use as handles turning the string into a saw. You might not even need the heat considering how degraded the adhesive is in it's current state.
I have an old VGA lcd pc monitor i suspect needs some new capacitors. When it has been off for some hours, it shows RGBW bars trying to start, then it shows the logo trying to start, but when it finally turns on, it works perfectly. I don't have the equipment or know how to fix it, so I bought a new one.
They're the first soldiers to die out in any electronic products after the battery of course.
They're very similar to a battery.
After 20 years old, sitting in a drawer unused they still can't work like new fresh ones.
Just like trying to charge dead battery, the ancient or tired from use Electrolytic capacitor (specifically) refuses to recharge anymore and just heats up and can cause other components to burn up.
They operate by a wet chemical reaction. Those chemicals age out and become no good anymore just like old beer. Not poison but not good drinking anymore.
Awesome JOB !
35:50 - you said center-tapped, but that is probably wound in a bifilar manner, with the “low end” of one winding connected to the “high end” of the other. Winding it in this manner ensures that each winding has equal turns to its counterpart, thus essentially equal voltage and essentially equal DC resistance.
I worked at Acme Electric in Cuba, NY before the CEO took the company private and destroyed company. Shortly after the Cuba division was sold off and then closed. Cuba was a great place to work.
Revive it If you can Adrian, that's what retro is trutly for and it seems cool too!
Another option instead of using another switch mode power supply if you did need to replace the original PSU would be to just use a small boost regulator on the 12V rail of the modern power supply (assuming the current isn’t too high).
I wonder if given that the glue goo seems to be soluble in IPA if you could soak the CRT face down in a shallow bath of IPA and then get that front glass separated.
saw some one post that soroc name is from coors beer and the logo is a look at the top of the can. not sure its true but interesting if it is.
Talking about power supplies, I was looking for something that would work well off a 2s li-ion battery and/or a 12v wall power supply and came across the MEZD41502A-C. It’s a little 2A boost converter that will run nicely off 5ish all the way to 12v. Unfortunately, Monolithic seems to have decided not to produce anymore of the pre-built module, though they publish a reference circuit and seem to want to keep the 12v version and base IC around.
Hi Adrian!
Regarding your concerns at the beginning of the video with respect to the mains power transformer not having all it's outputs loaded.
Well, good mains power transformers do not work like that!
Meaning, each output winding has it's own turn ratio with respect to the primary winding, and that is the only thing that sets ( or should be ) each output voltage.
If loading one winding, significantly reduces voltages on other windings, then that power transformer is poorly designed, because that can only happen when the primary winding is underrated ( not even high leakage inductance could do it, because that would further isolate the loaded winding ), meaning it's copper wire is too thin, and looses too much voltage under load.
A good mains power transformer should keep it's output voltages fairly constant no matter what winding is loaded, and by how much ( within specs, of course ).
Red locktight needs a bit of heat, but I guess you don't want too much heat on a Cap.
Melt off the tiny connection under the rubber seal. Also it can further dry out the already drying electrolyte making it even less worthwhile.
*Loctite.
I wanted to comment on the last video how it looks like that cap has started leaking and caught on fire while the machine was running, as I have an amplifier in my basement that had the same problem - the owner used it for PA of a soccer game and the match was just over and he wanted to pack in and it burst into flames. But those caps were running at 70V so I too didn't expect that at 9ish Volts. (and even though that happened in 1990, there was still some cap juice left)
I have witnessed when electrolytic capacitors leak, that conductive electrolyte can short out systems and cause a lot of problems. My bet is that electrolytic leaked onto the board and cause a short circuit that then burned the PCB.
If that is just a two layer (top/bottom) PCB you can cut or grind the PCB material away and rebuild it with off the shelf PCB repair stuff (like epoxy or some such), and then run copper tape "traces" to fix the PCB permanently. Had to learn how to do this at a previous job. Because we supported equipment that you may or may not be able to get replacement parts in a timely fashion. So we had to learn how to rebuild a PCB.
i remember the ads for this unit when i was little was fun times growing up in the early puter era :)
4:37 "It's pretty modern. I think it's from 1999" 1999 was a quarter of a century ago. However, I really think 1999 technology is more similar to today technology than either is to 1979 technology, so in a way, you're kinda right with the "modern" bit.
Soroc IQ120 is an interesting beast, with some of the functionality driven by EPROM based state machines, if I recall correctly. I worked on a few in the late 70s. The 7912 regulator is most likely for the negative rail on the RS232 drivers (MC1488...?), and the minus 5v from the zener would perhaps simply be a negative bias for a PMOS ROM or similar, so not that critical. (I've also got the manual in a pdf somewhere, but this is just from memory.)
Gracias por hacerlo entendible para los que hablamos español. Gracias.
1:20 - My 2 cents: Power up the board with bench supplies to see if it even works! I'm guessing many ICs may have been frapped during that flash-over!
I’ve seen the little caps in electronics pop violently. Not sure I would put my face that close to one that big.
I realize it’s a very controlled power which is a much safer and ideal situation.
Also, I've seen videos of people using heat guns to remove the protective crt screens to fix cataract issues.
Adrian have you ever thought about using BW100 for your electronics ?
I love those micro four thirds lenses also that 7-14mm should be good enough :)
That PCB section likely burned up from the electrolytic cap leaking electrolyte, shorting out the PCB chemically, burning it up
Kinda wanted to see you hook up that giant Pepsi-can capacitor to the ESR meter, seems like it would be amusing
Oh, the Plexus sitting there, cold... staring at us.
Hohoho... so lucky it was just the capacitor. I have high hopes this thing lives!
Linear power supplies are dead simple, so I would have begun with the transformer, and if it checked out, I’d doubled-down on repairing it as any of the components are simple and cheap.
I would have liked to have seen a multi-megohm measurement between the primary and secondary windings since you considered the transformer was suspect.
What Brainiac would use locktite on an electrical connection? You should only use that on a mechanical connection, for anything electrical just use lock washers!!!!
Putting that red loctite on the capacitor did seem a bit OTT.
I wondered about that. Screws in aluminium capacitors sometimes can become seized due to corrosion from the screw an capacitor thread being of dissimilar metals. I was thinking it might just be a residue from such corrosion.
Maybe all they had on hand at the time was
The beep was a good sign.
There is a company be the name of Meanwell that produces power supply units. You might be able to find what you are needing in their inventory.
It is a bit fun how things have developed. Here we see a computer that uses a simple 240 ohm 1 W resistor (R1 at 38:10) and a zener diode to provide 12 volt to the whole system, since it sees practically no meaningful load.
Meanwhile in modern computers, 12 volt is more or less the only source of power for everything.
Great, I really wanted to know if that capacitor was blown. So it was. I've seen smaller ones blowing holes in PCB's but they ran at higher volts inside an old switching PSU. Those where only 10 uF 450Volt capacitors. Imagine what a 15000 uF capacitor can do to your PCB.
Nice!
I'll get no price for this, but a shorted cap was my immediate thought when I saw the burned PCB. I can't see anything else causing this. Congrats on getting it back though. Did you replace the thermal compound on the linear regulator? Looking forward to part 3.
I wonder if the terminal got plugged in for testing decades later without letting that big capacitor reform correctly and the heat from the sudden current draw shorted it out through a c.ascade of fusing plates? 🤔
Me also, its always old electrolytics.. Great series..
Theres some great PCB artists around.. maybe someone could recreate the PCB from scans, etc. then it would be just a matter of transferring over as many of the intact and working over from the original.
Wow, that level of board damage reminds me of the testing reported by Sandia Labs in their TH-cam series "Always Never" about the safety and reliability of the systems controlling nuclear weapons. One of their discoveries was that electronics can do very strange and unexpected things when exposed to fire and other adverse environments. I wonder if that board is now electrically conductive? 🤔🤷♂
Who here clapped their hands when Adrian turned on the power switch to the transformer?
I'd be wary of using a modern ripple-laden switching PSU on these old parts. Like those ancient carbon resistors that need testing as well.