HP E3610A Power Supply - Current not displaying / Voltage not changing - Page 1
Forum section: electronics / repair

author: F4
author_rank: Contributor
timestamp: December 05, 2024, 12:15:42 am
content: I am having an issue with an E3610A repair. Does a schematic exist for the display board? Its not in the service manual.My issue is that the current display is always blank. It displays intermittently when set cc button is pressed and then goes blank again. All characters on the display work. At startup it flashes all the chars.The second symptom is that I get 15v at the output terminal and the display is unresponsive to the voltage dial. Both voltage and current pots have been checked.I cannot determine if the issue is the display board or the main board. I have tried testing the 4 transistors, swapping the 3 mainboard chips with a known working unit, cap replacement, and testing resistors/diodes around the current areas of the schematic. All voltage rails are spot on after the recap.Does anyone have the display board schematic? There seems to be 2 different display boards for this model, one having an extra pin and the older one without. 10 for the newer boards, 9 for the older.Anyone experienced a similar problem as this with one of this series (3610, 11, 12 etc)?Thanks!

author: F4
author_rank: Contributor
timestamp: December 05, 2024, 12:21:05 am
content: Here are a couple of pics of the older style display board, looks like 1991.

author: wn1fju
author_rank: Frequent Contributor
timestamp: December 05, 2024, 01:05:05 am
content: I don't have the display schematic, but I did have an E3611 that was behaving quite erratically. It is a known issue that the electrolytic capacitors on the main board leak, possibly from an inability to deal with the ripple or possibly from heat. In any event, they have a nasty habit of not only visibly leaking and possibly destroying traces on the board, but also leaking beneath the cap where you can't see it.If you haven't already, remove and inspect all of the electrolytics on the main board. Scrub the mainboard clean several times. Closely examine the board for any damaged traces and buzz the traces out with an ohmmeter if in doubt.This may not have anything to do with your display problem, but it might prevent additional problems in the future.

author: pqass
author_rank: Super Contributor
timestamp: December 05, 2024, 01:12:11 am
content: QuoteBefore embarking down the repair rabbit hole,you could just attach a multimeter (set to DCV) on the output terminals, then another multimeter (set to DCA) in series with the positive terminal, a power resistor(s), and the negative terminal. Twiddle the voltage and current knobs and see if your multimeters agree (with the built-in display and confirms ohms law) with the chosen power resistor(s) attached. Then you'll know which of the power supply regulation or the built-in display is the issue.

author: F4
author_rank: Contributor
timestamp: December 05, 2024, 11:12:04 am
content: Quote from: pqass on December 05, 2024, 01:12:11 amI have done something similar, the voltage knob does not respond to turning it on the display or the output. I get 15v on the output consistently. Current knob is also unresponsive.

author: pqass
author_rank: Super Contributor
timestamp: December 05, 2024, 11:28:27 pm
content: Quote from: F4 on December 05, 2024, 11:12:04 amLeave the display issue aside for now and use a trusted multimeter (in DCV) on the output terminals instead. Start with correcting the voltage regulation problem first so keep the current knob fully CW so it won't interfere with troubleshooting.See herefor a primer on how power supplies built on discrete components work. However, the generic voltage regulation described in the link differs slightly with your E3610A in that only one internal voltage reference (U3 output labeled "+5V") is used and the voltage divider is formed by R15+R37 (more on this later).Also, when reading the schematic (very endhere) that it is best to think of this power supply as being a negative supply. What I mean... when probing with your multimeter consider the positive output post to be 0V and the negative output post to be variable from 0V to -15V. Why? Because, the GND of the bipolar power supply (U2, U6) for the op amps is referenced to the positive output post (see the [+S] symbol, aka. TP6).Q:Without any load on the output terminals, confirm the voltages (multimeter on DCV with leads red:black) for TP1:TP6, TP8:TP6, TP5:TP6 which should be: +12V, -12V, +5V.Q:With the range button pressed (2A setting) and current knob fully CW, what is the voltage on TP7:TP6?Q:Is TP2:TP4 about +28V (an unloaded+rectified+filtered secondary at peak)?

author: F4
author_rank: Contributor
timestamp: December 07, 2024, 11:05:08 am
content: Quote from: pqass on December 05, 2024, 11:28:27 pmThanks for the link.When I posted before and said the rails were fine, I checked:TP9:TP10 - got 5vTP1:TP7 - got 12vTP5:TP7 - got 6.6v but saw somewhere that some of these meters were this voltage bc of a 320k resistor vs 1000k original to the boardTP8:TP7 - got -12vI tested according to your suggestion:(TP1:TP6, TP8:TP6, TP5:TP6 which should be: +12V, -12V, +5V)TP1:TP6, TP8:TP6, TP5:TP6 - all test okIs TP2:TP4 about +28V? More or less, getting 26vAnd found a problems:what is the voltage on TP7:TP6?Only getting .5v and seems to slowly trickly down, turning the current know ccw send the voltage to -.5v.Pin 1 on U4 shows 12v when referenced to TP7.TP7:TP6 seems to show a problem. Can you or anyone point me to a problem area to investigate? I tried to turn the 3 pots around that area (R20, 31, 19) which had no effect on the voltage at the meter.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 07, 2024, 11:28:14 am
content: Check the electrolitics, very common failure.Do you have oscilloscope? If so, check how it looks before and after the regulators.This SM has much better quality (But it's the same after all)https://elektrotanya.com/hp_e3610a_e3611a_e3612a_sm.pdf/download.html

author: pqass
author_rank: Super Contributor
timestamp: December 07, 2024, 04:40:34 pm
content: QuoteYes, you said the rails were fine but I wanted to confirm exactly what "fine" meant.I don't know why you're measuring relative to TP7 since TP7 is a moving target. It's controlled by the front panel set current knob.That's why you got 6.6V.Q:Which R? designator on the schematic are you saying was substituted (320k vs 1M)?QuoteThank you for confirming.Q:By "cap replacement" did you change C7 and C13?If so, the op amps are likely getting a good supply (bridge diodes and small value caps are likely just fine).QuoteThis is fine.QuoteDespite the name, "CREF"/TP7 is not a stable reference.Yes, you've found something interesting... TP7:TP6 (red:black DMM leads) should range from 0V to some negative single digit value (I calculate to be -6V) as you turn the front panel current knob CW.Changing R31,R32,R20 screws up the set current trimming and current display. You'll have to fix this later.And, U4A pin1 and TP7 should be connected; 12V difference?!Action item:To test/confirm voltage regulation is working, we can eliminate the current control from interfering with voltage regulation by lifting one leg of CR4 off the PCB. Since you've reported TP7:TP6 at -0.5V it would likely interfere.Report back to confirm that you have proper voltage regulation working (using an external DMM on the output terminals).First try with no load on the output terminals, then with a small load resistor.DON'T exceed 2A load(use ohms law or in-series DMM on DCA), since with CR4 lifted you don't have a current limit protecting the transformer, power transistors, etc.

author: F4
author_rank: Contributor
timestamp: December 08, 2024, 11:11:06 am
content: Quote from: pqass on December 07, 2024, 04:40:34 pmI based the measurement on what seemed like a ground reference, thanks for clarifying it.The resistor, yes, the schematic says 1k, the resistor measures 320, I read somewhere it was by design on the older revision, perhaps.Quote from: pqass on December 07, 2024, 04:40:34 pmYes, these 2 have been replaced. All electrolytics have been replaced. I bought this unit intentionally as a "save from the dead" for fun. Bad shape, both fuses F1 and F2 were blown, all kinds of exposed and deteriorated traces have been addressed and replaced CR9 and CR13. I have socketed the 3 chips and swapped them with a working unit and the working unit works fine, so its not the ICs.Quote from: pqass on December 07, 2024, 04:40:34 pmRemoving the leg of C4 had no impact, the behavior reported before, the .5v full cw, -.5v full ccw, remains the same. I did not test further, as I also notice U6 getting quite hot.The other thing I see is that 26v is at the output terminal now. I recall measuring 15v here in the past, not sure when this change happened, though.Let me work on the regulation a bit more and then try the load resistor.

author: F4
author_rank: Contributor
timestamp: December 08, 2024, 11:22:29 am
content: Quote from: DavidAlfa on December 07, 2024, 11:28:14 amYep, all caps replaced. Looks like it was damaged in the past from electrolyte.

author: pqass
author_rank: Super Contributor
timestamp: December 08, 2024, 05:07:32 pm
content: QuoteEither value doesn't matter; 7mA vs 22mA through zener U3 is fine to produce a stable +5V reference for R15.QuoteGood.Hmm.... sounds like you're in for a treat.QuoteBy lifting CR4, we removed current limiting capability entirely. We needed to do this to determine if the unit can even do simple voltage regulation first. So never mind TP7 output for now.I don't know why the -12V regulator (U6) is getting hot; there's only the op amp supplies and Q2 collector connected to it. I suggest you remove U4 and U5 for now (and with CR4 lifted, they aren't needed to test the voltage regulation loop).Because you've reported that +26V appears on the output, that means that R3 is pulling up on Q1,Q3 (darlington) bases to turn them fully ON (ie. no voltage regulation). So Q2 is off/broken or there's a broken trace somewhere from Q1,Q3 bases to U1 pin 6 (op amp output).See attached simplified E3610A voltage regulation loop pix and onlinesimulation here. I've removed all protection diodes or tweak components that aren't relevant to understanding how the loop works.The service manual schematic is written for all three models in the series but for the E3610A many components are jumpered or unpopulated. Specifically, unpopulated: Q6, Q7, Q4, Q5, C22, C23, R43, JP1, jumpered: R38, R39, R44, R45, JP2.Get voltage regulation working first without any load; looking for trace breaks or open/shorted components in the loop. Then, after the loop is working, add a load and see if it still maintains the same voltage (DON'T draw more than 2A). Then we'll work on the current limiting parts (putting back CR4, U4, U5).

author: F4
author_rank: Contributor
timestamp: December 15, 2024, 01:05:11 pm
content: Quote from: pqass on December 08, 2024, 05:07:32 pmThank you for the assistance and the diagram. I've had a chance to work on this unit some more, I thought I had it licked but it insists on being stubborn.In going thru the traces I decided to replace R29 and R30, which looked worse for wear. After removal I started to test continuity and saw that pin 7 and 8 of U5 were incorrectly repaired. The trace from R28 was attached to pin 8 instead of 7.I put everything back together to see if this remedied everything, it did not. On the plus side, the output at the terminals is now -17v across both the + and - terminals. Since its a 15v supply, this is progress. Unfortunately it does not respond to the knobs for either voltage or current.Q2 was replaced a while ago, but put a new one in just in case, same behavior.U6 remains hot. I double checked the caps for polarity. U6 is drawing current, would the CC set be the area drawing that current it? U6 was also replaced previously, by the way.I tested the TO3 transistors (Q1,3) in circuit with the diode setting, I got proper beeps from them with testing across CBE. I also went thru and took out and tested all the black DALE resistors, all looked good. Should I pull Q1/3 and test it further?

author: nvmR
author_rank: Regular Contributor
timestamp: December 15, 2024, 01:25:08 pm
content: I have a similar puppy, misbehaving in the voltage reading. It may sound trivial, but double check the cable between the main and the display panel. Mine was finicky.Also, check AC at the output. I once saw one that like to give some 3V AC along with the required DC. fun fun fun

author: pqass
author_rank: Super Contributor
timestamp: December 16, 2024, 08:53:53 pm
content: Quote from: F4 on December 15, 2024, 01:05:11 pmR29 and R30 are just used to limit the current to the CV and CC LEDs. U5 (LM393 comparator) drives their output (pin 1 or 7) to -12V if +Vin (pin 3 or 5) goes below +9.8V (center of R25+R41 divider); lighting up the LEDs at 24mA (24V/1K, hence the 1W resistors)!!! Whichever the Current Error Amp or Voltage Error Amp is controlling the output voltage (via CR4 or CR5 switching), the other will output close to +12V which will disable its corresponding LED.R28 is in the CREF parts; you probably mean R29 was incorrectly tied to pin 8 (+12V). That would always keep the CC LED off.Given potentially many issues with this board, if you haven't already done so, clean the board with generous amounts of IPA to remove all gunk/film. Also inspect all obvious (non-factory) changes or damage/cracks.QuoteIf the output at the terminals is -17V (assuming your DMM on DCV leads were reversed), then this is an improvement. The resistor divider formed by R15 (14.3K) and R37 (50K front-panel voltage pot) would produce 17V outputIFthe wiper on R37 was open/disconnected or stuck at max range.Q:With the unit powered-off, if you isolate R37 from the circuit (disconnect wire from PCB to one pot terminal), does it still vary from 0 to 50K (wiper still attached to one pot terminal)? Put the wire back onto the pot terminal once you've checked R37s resistance.This next test assumes that one CR4 lead is still lifted off the PCB, thus current limiting won't be affecting the output voltage and only the Voltage Error Amp is controlling the output voltage.Q:Although the voltage setting knob has no effect, can you apply a small resistance to the output terminals (try in the range of: 330R, 220R, 100R, 50R) and does the voltage stay the same? ie. can it regulate regardless of attached load? Don't use <20R @17V as that is 850mA and >10W.QuoteU6 (-12V regulator) being hot is unusual. I can barely feel it in my E3611A.Q:Let the unit cool down then remove all three ICs U1, U4, U5. Turn the unit back on (output terminals will be at 26V, that's okay). Does U6 (-12V regulator) get hot?If no, then turn the unit off and put back U1 and turn it back on. Does U6 get hot?If no again, then the issue is the other U4 or U5 or in their parts of the circuit. Leave U4 and U5 out for now and concentrate on getting voltage regulation working.If U6 gets hot with only U1 installed it could be U1 or Q2 again. Or, maybe something else (non-factory) pulling on -12V.QuoteTroubleshooting should be methodical. After checking the obvious stuff like (a) all power supplies producing the correct voltages, (b) obvious damage areas or faulting components (bulging caps), then you need to isolate sections and work your way from the (measured) good parts until you find the unexpected. Yes it's good to replace problem components like electrolyic/tantalum caps and swapping ICs for known good ones, but just random checking or replacing rarely solves the problem(s).This is why I've asked you to lift one end of CR4, in order to isolate the current limiting parts from controlling the voltage at the output terminals. So we can concentrate on fixing the voltage regulation first. Sometimes schematics are hard to read, so I hope I've given you enough clear information on the Voltage Regulation loop for you to find the "unexpected" in it. For a detailed explanation of how the voltage regulation loop works see a previous post of minehere.

author: F4
author_rank: Contributor
timestamp: December 17, 2024, 06:50:54 pm
content: Quote from: nvmR on December 15, 2024, 01:25:08 pmChecked that, no AC at the output

author: F4
author_rank: Contributor
timestamp: December 17, 2024, 07:02:54 pm
content: Quote from: pqass on December 16, 2024, 08:53:53 pmYes, R29. I've inspected and inspected, ha ha.Quote from: pqass on December 16, 2024, 08:53:53 pmI have not performed this test yet, see below.Quote from: pqass on December 16, 2024, 08:53:53 pmAfter removing the IC, the same behavior persisted, U6 is hot. I detached CR4 again, same.I grabbed my FLIR and looked at it and saw that CR6 was also hot, and Q2. I decided to change CR6 (7, 10 and 11 as well) just to be safe. No change in the behavior, these components are getting hot. CR6 is part of the voltage error amplifier, but I am still too novice to understand why it's drawing current.I am continuing to look at the board, but wanted to share that CR6 is also hot.

author: pqass
author_rank: Super Contributor
timestamp: December 17, 2024, 09:02:42 pm
content: QuoteCR6 and CR7 are protection diodes; keeps U1 +Vin to -Vin difference to below 0.7V. (FYI: JP1 is open, JP2 is shorted) Neither one should get hot.But CR6 can get hot if the Voltage Control pot (R37) is fully CCW and the loop isn't regulating possibly due to a break between U1 output to Q1,Q3 base. CR6 and R13 (1K) can get hot because they're between Q1,Q3 (letting too much voltage through at [+S]) and R37 (at low ohms when CCW) to TP4. For now, just keep the Voltage Control pot (R37) at mid-point; don't dial all the way down until we get voltage regulation working.a.Check if CR5, CR6, CR7, CR8 are still diodes with your DMM on diode-check; lift one leg to be sure. Confirm working diodes before proceeding to the next step.b.Keep R37 pot at mid-point and one CR4 leg lifted. Then lift CR5 cathode off the PCB. Turn the unit on, you should see 26V on the output terminals. Why? Because Q2 is off pulled up by R5. And R3 turns Q1,Q3 fully-on.Now, with an alligator-clip jumper wire, momentarily (<20 seconds) connect -12V (TP8) to the lifted (unconnected) CR5 cathode. What should happen is that Q2 should be fully turned on, which pulls the Q1,Q3 bases down (shutting them off) and the output terminals should read 0V (or close too it). If this occurs like I describe then the problem is before CR5 toward U1. If not, the problem is after CR5 toward Q2. Report back.

author: F4
author_rank: Contributor
timestamp: December 21, 2024, 12:02:27 pm
content: Quote from: pqass on December 17, 2024, 09:02:42 pmYes, they are. CR6, 7 and 8 have been swapped already and all 4 check out on the DMM.Quote from: pqass on December 17, 2024, 09:02:42 pmI put back CR7 and 8, did as instructed here, but got 0 volts at the output. I thought it was the ICs missing, so I put those 3 back but the behavior was the same, 0v.Quote from: pqass on December 17, 2024, 09:02:42 pmWith the result of the previous test, I went ahead and did this one anyway. I did get 0v but am not sure this is relevant as to whether the problem still between CR5 and towards U1 considering I did not see 26v on the output terminals?When you say CR5 towards U1, does that mean pulling and checking all the parts in this red blob?

author: pqass
author_rank: Super Contributor
timestamp: December 21, 2024, 04:11:43 pm
content: Quote from: F4 on December 21, 2024, 12:02:27 pmIf CR4 and CR5 each have one leg disconnected from the PCB, and there's STILL 0V on the output terminals, then that means Q1,Q3 are turned off or permanently open (broken). Or, assuming R3 and R5 pull-ups are working, then the only possibility is Q2 is always conducting (broken).For now, we need to work from Q1,Q3 thru Q2 to U1 output. Upstream of U1 can wait until the driver transistors are confirmed working first.a.Start by confirming R3,Q1,Q3 are working by pulling-off Q2 from the PCB (watch out for the ferrite bead on the emitter leg and mark the orientation on the PCB). You should see 26V on the output terminals. If not, STOP here.b.If previous step sees 26V on the output, then we want to see if we can shut off Q1,Q3 by using an alligator jumper wire shorting TP3 with the PCB pad that Q2 emitter occupied. You should now see 0V on the output terminals.c.If the previous step sees 0V, then test Q2 as it may be permanently shorted. Replace Q2 (you may get away with a 2N3906 or other small signal PNP transistor temporarily) and re-do theb.test and following paragraph again (from my previous post).QuoteCorrect' it's not relevant. This test is premature given that we didn't get 26V on theb.test. We now have to work toward Q1,Q3 instead.QuoteYes but hopefully we won't need to pull and test everything in the loop. This is why I started with D5 (mid-point in the loop). I was hoping at least half of it (Q1,Q3 to D5) was working but since we never got 26V on the output terminals (with the loop broken at D5), then we have to work toward Q1,Q3 until we can be sure those components are working. Once everything from Q1,Q3 to D5 works as expected, we'll then work from D5 to U1 output (and U1 input components too).

author: F4
author_rank: Contributor
timestamp: December 30, 2024, 04:51:56 pm
content: Quote from: pqass on December 21, 2024, 04:11:43 pmI had spent some of yesterday pulling the unit apart, including the back heatsync, etc, to give a clean and check Q1 and Q2. They were fine, I changed them at the beginning of the project. I pulled several resistors along the path and checked them. Managed to break CR5, so I needed to order some diodes too. It did not affect my ability to test. None of the stuff I looked at failed.I pulled Q2, which is also changed from the beginning and it still checks out.The other thing I found is somewhere along the way I mixed up the chips so put them in their right places, I thought for a while this was the root problem, but the unit behaved the same when I put it back together, U6 still heating up. There is more responsiveness from the dials now, on the bright side.Pulling Q2 resulted at 0V at the output so I stopped there, and U6 no longer heats up.I am going to test the 3 chips from a known good unit against this one again and see if mixing the order ruined that swap test last time and one of the ICs is in fact bad.You assistance is appreciated, I would have likely given up by now from frustration, and I have learned a lot sticking with it.EDIT: I made a mistake, I am pulling 12v at the output on the previous test.

author: pqass
author_rank: Super Contributor
timestamp: December 31, 2024, 02:52:24 pm
content: QuoteYou mean, pulling Q2 off the PCB gives 12V at the output terminals?If so, it would appear that Q1,Q3 are being partially turned on but notfullyturned on. See attached.This is a problem. You must correct this before worrying about other components.It could be one or both (Q1 or Q3) are bad. Yes, you've tested them but have you tried a simple switch test? See attached.If you find one power transistor works but the other doesn't, pull the bad one and move on (with testing) down the loop (fromb.in myreply#17; adding back Q2, CR5 leg lifted, etc.).While one (Q1 or Q3) is removed, don't pull too much current (<0.5A) in your testing until you replace it. If both are bad, then you probably can get by with any spare beefy NPN darlington you may have on-hand. Again, don't pull too much current in your testing until they can be replaced with equivalents. Although, finding TO-3 cased darlingtons may be expensive. You may have to improvise with TO-247 packaged equivalents.Try not to be frustrated. Take baby steps from known good working parts slowly solving each problem in the loop toward U1 and R37

author: garrettm
author_rank: Frequent Contributor
timestamp: January 01, 2025, 08:57:19 pm
content: I've "fixed" over 10 of these older HP/Agilent PSUs. Every one of them had oxidized contacts on the front panel push-button switches. And if there are slide switches on the backside to allow for tracking and multi-unit connection ("master"/"slave" etc.), then check them too. I had to remove all the rear switches on 4 different units. Ended up replacing with wire jumpers because new switches were too expensive (replacements would have cost more than the PSU!).The front panel switches cannot be fully disassembled (unlike older switches of the same type), so you will likely have to unsolder and ultrasonicate in a dispersant (to remove the silicone lubricant) and then ultrasonicate with a silver cleaning solution, rinse in distilled water, dry with compressed air, and then do a final spray with fresh silicone lubricant to keep the contacts from oxidizing and lower friction of the plastic parts.

author: artag
author_rank: Super Contributor
timestamp: August 10, 2025, 11:30:38 am
content: You're doing better than me.How do you even get the lid off ?

author: macboy
author_rank: Super Contributor
timestamp: August 10, 2025, 01:22:39 pm
content: The lid has big retention tabs, one in each side near the back. You need to gently lift these away from the metal frame using a flat screwdriver or similar. Then lift the rear of the lid enough to slide the lid backward a little. This releases the lid front which is held in place by tucking under the front panel. (This is based on my E3620A which I assume are the same lid).

author: artag
author_rank: Super Contributor
timestamp: August 10, 2025, 05:47:37 pm
content: Got it, thanks !