Great repair journey, thanks for sharing not just the "I found this and fixed it" that is so common on repair videos. Your 'hmm, I wonder..." and "that's not what I expected" curiosity is essential in complex repairs. Interesting failure mode, as far as I remember, I've only seen tantalums exhibit dead-shorts in a long career of repairs, so that's a useful data point, thanks!
Thank you so much for your comment and watching! I really appreciate it. Unfortunately I can't always give the details as to why a failure/fault symptom has occurred because I'm still learning electronics myself. So in my videos I may be learning a new skill or concept in real-time. They don't make for good tutorials, but I don't pass them off as such. I am working towards making them shorter/better editing. Thanks again for your feedback and for watching!
On those metal spring switches slide out metal flat spring and flip them. buttons will be smooth instead of sticking and making loud click sound, don't try to remove the switch just slide the metal out, flip and reinstall, I do this on all HP gear that uses these type of switches, it make them smoother and nicer to use. When ever replacing diodes that when short and burn up always check for shorts. Always remove Rifa capacitors, I seen those take out the primary mosfet and diodes almost instantly. They won't always just blow and catch fire which is what they are famous for, I had a few just dead short and actually look fine no cracking and etc and was dead shorted. Like you found the filters go bad on theses as well. You definitely doing a great job as far as troubleshooting and fixing, just made comment to save you hassle of blowing up new parts and saving you some time and hassle in the future as I repair test equipment as work at a calibration lab for years and seen it all over the years. It is a great piece of test equipment and you got a good deal for a great power supply. Those HP supplies are quite reliable and well built once fixed up completely. Built a dim bulb tester, it save you fuse and tripping breaker. On switch mode supplies start with a 150w bulb and higher as power supply won't start if wattage is to low. That a very good DER LCR meter I have the same one as good as my more expensive Keysight LCR meter both are pretty accurate.
Thank you for the tips and feedback! I've been meaning to make myself a dim bulb tester. This is one of the reasons I made this channel - to learn from people like yourself with more experience! Really appreciate you taking the time to write your comment and watch!
40:29 Its unusual to see a cap go completely dead short, especially a Sprague one. It wasn't bulging or leaking and only has 20V across it, way under it's 35V rating.. Sprague are high quality. Ive seen lots of cheap chinese caps fail short but never Sprague.
Ive come across a few faulty Sprague caps in my repairs (see also my vid on repairing a Tektronix 576 curve tracer)th-cam.com/video/BUa7K98w2yg/w-d-xo.htmlsi=AL-5adkvGk11DyLZ
Excellent work and it takes me back seeing you working on the carpet floor at home ! One thing I will say and I don't want to criticise but check for direct shorts across the supply's as a matter of course before power up as this would have saved a bit of time. You seem to have great enthusiasm and skills so good luck with the rest and I am waiting for part 2 which will be test and calibrate I expect !....cheers.!
thank you always for your input! I would also like to build an incandescent lamp set-up to connect in series with supply for detecting shorts/mitigating damage to the DUT. And yes I have a small apartment at the moment - there's no where else to work at home on this kind of stuff lol. Need a GPIB controller to do the calibration - I ordered one so I'll get on with the next part as soon as it gets here! Thanks again!
Just a few pointers to make your repair a little easier and less frustrating. Firstly, get yourself a few incandescent light globes, 100w, 150 w and 200w, make up a rig with switches so you can put them in paralell…then put that paralell arrangment IN SERIES with the active/phase/line lead of the piece of potentially faulty gear you have just acquited and seek to repair. If, for whatever capricious reason the piece of gear chooses, or has already chosen to go low impedance and present a low port impedance at its mains connection, the worst that will happen is the globe(s) will light up, and provide some protection to the device under test….but more importantly it /they will almost instantly warn you that the device has gon low impedance and is attempting to dissipate a TON of power internally and potentially dammage itself further! Getting more specific to this device, I hsve pulled up the circuit diagram online so I can see what you can see. The circuit diagram IS YOUR FRIEND, it will tell you a sh!t-ton about your device in an instant, a lot more than pages and pages if text can and in a far shorter timespan. So this thing is a switchmode power supply, the main, high powered part is switchmode and that is what you were powering from your bench supply st home on the floor. Now there is a second linear auxillary supply that uses a standard iron cored transformer and thise two “over-red-in-the-face” diodes were part of a centre tapped full bridge supplying + and - inreg rails to all the auxillary stuff in there. The two dammaged diodes are supplying +20v to Q3, (A buck-down reg to +5v that I suspect powers all the TTL logic in in the control part of the unit), the +20v from your two said diodes also supplies linear reg, U4 which is the source of an 8.4v rail. I tend to follow (“the money”), i.e. the fault current path in this type of repair which would be via either Q3 or U4. Another “Friend in the workshop” is your multimeter, (I am assuming you hav one or access to one at your workplace), particularly the “diode bias continuity” function. I’d be “pouncing on” both U4 and Q3 immediatly with that diode test function, I’d also check CR11, the buck back-EMF catch diode in the 20 Down to 5v buck-reg, if it is shorted it will give you grief! Also note the “drop-link”, W2, Pulling this out allows you to disconnect the vast bulk of the +5v load (and any potential capricious low impedances it might be hiding) allowing you to rapidly blame or eliminate the buck-converter and/or its load. So if you pull W2 and power up and the light globes srill come up bright, the fault is in the buck-reg, U4 or its load, if the globes “pulse” from the charging up of the big filter caps, the fault is in Either U9, (unlikely) or further down that +5v rail, (far more likely). Thank your lucky stars the fault is not a catastrophic one in the main high powered switchmode path, or even a non catastrophic one…which a harder to find as there are now outward physical signs you can see or smell! It has to be microprocessor controlled, U14. The fact all the seven segs and LEDs in the front psnnel sre full lit is not a good sign. Once you find the capricious low lmpedance fault (short) on the +5v line, next would be to see if the micro has been “hurt”, get your oscilloscope probe and dive straight for quarts clock crystal Y2 to see if there is any RF there, if not, the micro is probably buggered and you will be “up the creek in a barbed wire canoe” as we say here in Tasmania! If Y2 is oscillating you are good to go to find further faults. Again, if ROM chips have been damaged, you are in for far more grief than a normal fix because you need to not only procure the ROM itself, but the code that was on it too! Tekwiki provides a lot of such code for old Tek stuff, but there does not seem to be such a centralized dource for HP stuff. Good luck, and I will be watching with keen interest to see how you get along, but remember a few incandescent light globes and a multimeter can get you there a lot faster and with less magic smoke!
Thank you for that wealth of info! I've been meaning to build myself an incandescent bulb setup to put in series with the supply for testing. But yea I could have utilized both my meter and the scope a bit more in this vid. Though if you watch to the end, I did find the fault. It was C23 which is across the 20V unregulated supply to smooth out the rectified signal. I replaced it and now the front panel is responding normally to commands. Next video will be further testing, calibration and performance evaluation. But thanks for taking the time to watch and write your response! This is exactly one of the reasons why I made this channel for - to learn more from those with more experience!
Good repair! It is a nice power supply albeit a bit noisy. Here is the list of the RIFA caps on the base boar. And yes you should replace these a-s-a-p. 15mm C16 - 0.01µF / Y / 250V / 15mm C22 - 4700pF / Y / 250V / 10mm C23 - 4700pF / Y / 250V / 10mm C24 - 2200pF / Y / 250V / 10mm C25 - 2200pF / Y / 250V / 10mm C26 - 0.047µF / X2 / 250V
@@fmashockie Have updated the post with size and type of safety capacitor. If I remember well the 15mm wide ones are a bit difficult to find and I ended up replacing it with a 17mm wide and bent te legs a little. I did not take note of the size of C26 apparently.
Good point! I completely forgot about that. I just bought all my home test equipment not all that long ago. Don't use it that often because I'm mostly in the lab at my work. But good catch and thanks!
Just watched the rest of it where you found C23 shorted. That 8.4v reg, U4….linear regs don’t generally like an output voltage that is greater than their input voltage, so when C23 shorted to would have Slammed the +20v unreg rail to zero in an instant, so U4 will have had 0v in and 8.4v out for a short while before its output decoupling cap, C7 had a chance to discharge, so I,d be straight to checking thst 8v4 rail (driving T1 and the gayes of the main switchmode MOSFETs. If you look in the old National Semiconductor Linear (Devices) Data Book…the “Blue Bible” you will see…inder the LM317, how to place a reverse biased diode from in back to out of a linear reg to provide a discharge psth for any dscoupling caps on the output side in the event of a sudden loss of the input.
Thank you again for input! I'll left out the two additional bias supply rails 8.9 and 2.5 in this video. But I will be doing a lot more additional testing in the next vid. Really appreciate your comments and for taking the time to write them!
Oh, forgot to warn you, if Q3 has shorted and dumpped the full +20v unreg onto the +5v TTL rail…..well “you will be paddling like mad against the brown sewer tide in that aforementioned barbed wire canoe”! geez I hope I havn’t jinxed you! (‘scuse all my typos but Im om a tiny gadget.)
Yep... I took a bit of a gamble buying this in the first place because I was aware of the fault. My first thought was an issue with the micro/ROM chips due to short that destroyed the digital side. Fortunately, that C23 filter cap was the cause and those rectifier diodes took the brunt of the damage. Still have more testing to do to rule out any further damage! Thanks for all your input!
I truly do not mean to slam you, but I had to stop watching the video, because you are waving the camera around so much that it is making me uncomfortable. You will get better at video production, over time, so stick with it. Maybe make, or buy, a camera mount. I hope this feedback is helpful.
@@pooptrux good point! I'll try to start implementing that. I really need to upgrade my tools for recording anyway. Thanks for still sitting thru it and watching!
Great repair journey, thanks for sharing not just the "I found this and fixed it" that is so common on repair videos. Your 'hmm, I wonder..." and "that's not what I expected" curiosity is essential in complex repairs. Interesting failure mode, as far as I remember, I've only seen tantalums exhibit dead-shorts in a long career of repairs, so that's a useful data point, thanks!
Thank you so much for your comment and watching! I really appreciate it. Unfortunately I can't always give the details as to why a failure/fault symptom has occurred because I'm still learning electronics myself. So in my videos I may be learning a new skill or concept in real-time. They don't make for good tutorials, but I don't pass them off as such. I am working towards making them shorter/better editing. Thanks again for your feedback and for watching!
On those metal spring switches slide out metal flat spring and flip them. buttons will be smooth instead of sticking and making loud click sound, don't try to remove the switch just slide the metal out, flip and reinstall, I do this on all HP gear that uses these type of switches, it make them smoother and nicer to use. When ever replacing diodes that when short and burn up always check for shorts. Always remove Rifa capacitors, I seen those take out the primary mosfet and diodes almost instantly. They won't always just blow and catch fire which is what they are famous for, I had a few just dead short and actually look fine no cracking and etc and was dead shorted. Like you found the filters go bad on theses as well. You definitely doing a great job as far as troubleshooting and fixing, just made comment to save you hassle of blowing up new parts and saving you some time and hassle in the future as I repair test equipment as work at a calibration lab for years and seen it all over the years. It is a great piece of test equipment and you got a good deal for a great power supply. Those HP supplies are quite reliable and well built once fixed up completely.
Built a dim bulb tester, it save you fuse and tripping breaker. On switch mode supplies start with a 150w bulb and higher as power supply won't start if wattage is to low. That a very good DER LCR meter I have the same one as good as my more expensive Keysight LCR meter both are pretty accurate.
Thank you for the tips and feedback! I've been meaning to make myself a dim bulb tester. This is one of the reasons I made this channel - to learn from people like yourself with more experience! Really appreciate you taking the time to write your comment and watch!
40:29 Its unusual to see a cap go completely dead short, especially a Sprague one. It wasn't bulging or leaking and only has 20V across it, way under it's 35V rating.. Sprague are high quality. Ive seen lots of cheap chinese caps fail short but never Sprague.
Ive come across a few faulty Sprague caps in my repairs (see also my vid on repairing a Tektronix 576 curve tracer)th-cam.com/video/BUa7K98w2yg/w-d-xo.htmlsi=AL-5adkvGk11DyLZ
Excellent work and it takes me back seeing you working on the carpet floor at home ! One thing I will say and I don't want to criticise but check for direct shorts across the supply's as a matter of course before power up as this would have saved a bit of time. You seem to have great enthusiasm and skills so good luck with the rest and I am waiting for part 2 which will be test and calibrate I expect !....cheers.!
thank you always for your input! I would also like to build an incandescent lamp set-up to connect in series with supply for detecting shorts/mitigating damage to the DUT. And yes I have a small apartment at the moment - there's no where else to work at home on this kind of stuff lol. Need a GPIB controller to do the calibration - I ordered one so I'll get on with the next part as soon as it gets here! Thanks again!
Just a few pointers to make your repair a little easier and less frustrating. Firstly, get yourself a few incandescent light globes, 100w, 150 w and 200w, make up a rig with switches so you can put them in paralell…then put that paralell arrangment IN SERIES with the active/phase/line lead of the piece of potentially faulty gear you have just acquited and seek to repair.
If, for whatever capricious reason the piece of gear chooses, or has already chosen to go low impedance and present a low port impedance at its mains connection, the worst that will happen is the globe(s) will light up, and provide some protection to the device under test….but more importantly it /they will almost instantly warn you that the device has gon low impedance and is attempting to dissipate a TON of power internally and potentially dammage itself further!
Getting more specific to this device, I hsve pulled up the circuit diagram online so I can see what you can see. The circuit diagram IS YOUR FRIEND, it will tell you a sh!t-ton about your device in an instant, a lot more than pages and pages if text can and in a far shorter timespan. So this thing is a switchmode power supply, the main, high powered part is switchmode and that is what you were powering from your bench supply st home on the floor. Now there is a second linear auxillary supply that uses a standard iron cored transformer and thise two “over-red-in-the-face” diodes were part of a centre tapped full bridge supplying + and - inreg rails to all the auxillary stuff in there. The two dammaged diodes are supplying +20v to Q3, (A buck-down reg to +5v that I suspect powers all the TTL logic in in the control part of the unit), the +20v from your two said diodes also supplies linear reg, U4 which is the source of an 8.4v rail. I tend to follow (“the money”), i.e. the fault current path in this type of repair which would be via either Q3 or U4.
Another “Friend in the workshop” is your multimeter, (I am assuming you hav one or access to one at your workplace), particularly the “diode bias continuity” function. I’d be “pouncing on” both U4 and Q3 immediatly with that diode test function, I’d also check CR11, the buck back-EMF catch diode in the 20 Down to 5v buck-reg, if it is shorted it will give you grief! Also note the “drop-link”, W2, Pulling this out allows you to disconnect the vast bulk of the +5v load (and any potential capricious low impedances it might be hiding) allowing you to rapidly blame or eliminate the buck-converter and/or its load. So if you pull W2 and power up and the light globes srill come up bright, the fault is in the buck-reg, U4 or its load, if the globes “pulse” from the charging up of the big filter caps, the fault is in Either U9, (unlikely) or further down that +5v rail, (far more likely). Thank your lucky stars the fault is not a catastrophic one in the main high powered switchmode path, or even a non catastrophic one…which a harder to find as there are now outward physical signs you can see or smell!
It has to be microprocessor controlled, U14. The fact all the seven segs and LEDs in the front psnnel sre full lit is not a good sign. Once you find the capricious low lmpedance fault (short) on the +5v line, next would be to see if the micro has been “hurt”, get your oscilloscope probe and dive straight for quarts clock crystal Y2 to see if there is any RF there, if not, the micro is probably buggered and you will be “up the creek in a barbed wire canoe” as we say here in Tasmania! If Y2 is oscillating you are good to go to find further faults. Again, if ROM chips have been damaged, you are in for far more grief than a normal fix because you need to not only procure the ROM itself, but the code that was on it too! Tekwiki provides a lot of such code for old Tek stuff, but there does not seem to be such a centralized dource for HP stuff.
Good luck, and I will be watching with keen interest to see how you get along, but remember a few incandescent light globes and a multimeter can get you there a lot faster and with less magic smoke!
Thank you for that wealth of info! I've been meaning to build myself an incandescent bulb setup to put in series with the supply for testing. But yea I could have utilized both my meter and the scope a bit more in this vid. Though if you watch to the end, I did find the fault. It was C23 which is across the 20V unregulated supply to smooth out the rectified signal. I replaced it and now the front panel is responding normally to commands. Next video will be further testing, calibration and performance evaluation. But thanks for taking the time to watch and write your response! This is exactly one of the reasons why I made this channel for - to learn more from those with more experience!
Good repair! It is a nice power supply albeit a bit noisy. Here is the list of the RIFA caps on the base boar. And yes you should replace these a-s-a-p.
15mm
C16 - 0.01µF / Y / 250V / 15mm
C22 - 4700pF / Y / 250V / 10mm
C23 - 4700pF / Y / 250V / 10mm
C24 - 2200pF / Y / 250V / 10mm
C25 - 2200pF / Y / 250V / 10mm
C26 - 0.047µF / X2 / 250V
Thanks for taking the time to post those I really appreciate it! I'll be doing those replacements in part 2 🙂
@@fmashockie Have updated the post with size and type of safety capacitor. If I remember well the 15mm wide ones are a bit difficult to find and I ended up replacing it with a 17mm wide and bent te legs a little. I did not take note of the size of C26 apparently.
Your power supply can be put in series to make the 40ish volts needed. Why don’t you use that?
Good point! I completely forgot about that. I just bought all my home test equipment not all that long ago. Don't use it that often because I'm mostly in the lab at my work. But good catch and thanks!
Just watched the rest of it where you found C23 shorted. That 8.4v reg, U4….linear regs don’t generally like an output voltage that is greater than their input voltage, so when C23 shorted to would have Slammed the +20v unreg rail to zero in an instant, so U4 will have had 0v in and 8.4v out for a short while before its output decoupling cap, C7 had a chance to discharge, so I,d be straight to checking thst 8v4 rail (driving T1 and the gayes of the main switchmode MOSFETs.
If you look in the old National Semiconductor Linear (Devices) Data Book…the “Blue Bible” you will see…inder the LM317, how to place a reverse biased diode from in back to out of a linear reg to provide a discharge psth for any dscoupling caps on the output side in the event of a sudden loss of the input.
Thank you again for input! I'll left out the two additional bias supply rails 8.9 and 2.5 in this video. But I will be doing a lot more additional testing in the next vid. Really appreciate your comments and for taking the time to write them!
...and Agilent is now Keysight
Oh, forgot to warn you, if Q3 has shorted and dumpped the full +20v unreg onto the +5v TTL rail…..well “you will be paddling like mad against the brown sewer tide in that aforementioned barbed wire canoe”! geez I hope I havn’t jinxed you! (‘scuse all my typos but Im om a tiny gadget.)
Yep... I took a bit of a gamble buying this in the first place because I was aware of the fault. My first thought was an issue with the micro/ROM chips due to short that destroyed the digital side. Fortunately, that C23 filter cap was the cause and those rectifier diodes took the brunt of the damage. Still have more testing to do to rule out any further damage! Thanks for all your input!
Dim light bulb for current limiting.
thanks for the feedback! I've been meaning to build myself one of those for quite some time!
I truly do not mean to slam you, but I had to stop watching the video, because you are waving the camera around so much that it is making me uncomfortable. You will get better at video production, over time, so stick with it. Maybe make, or buy, a camera mount. I hope this feedback is helpful.
yea I apologize for that. I do need to get a better setup for recording video. But I appreciate the feedback!
@@fmashockie Any time you're thinking of pointing your camera at the screen, use a screen recorder instead. I look forward to part 2!
@@pooptrux good point! I'll try to start implementing that. I really need to upgrade my tools for recording anyway. Thanks for still sitting thru it and watching!
A further hint would be to cut a lot of the waffle. This could have been more to the point at 20 minutes or so rather than 50.
Thanks Brian I gotta get better at making these shorter. But I appreciate the feedback!@@Brian_Of_Melbourne
Good video mate, but try not to do all the sniffing and snotting on a live mike, sounds disgusting!
😂thank you for your feedback! I'll try to remember that for next time
ave enjoyer