HP 6177A repair (fixed) - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: July 31, 2024, 02:23:28 am
content: Edit:The 6177A was dismantled and then I got a 6181C. Then I broke it after fixing it some how, got another 6181C, found that its just the wiring somehow, then I fixed that, and I have 2x 6181C that are fully restored and working. I warn that the A versions are only for people seeking adventureI am still not done repairing this thing. I replaced all the passive components, and the diodes, and a majority of the transistors and a light bulb. I thought I over looked one of the output transistors on the heatsink, so I bought new ones, but when I totally removed the old ones from circuit they seem to measure OK.Well since I bought new ones, I will replace them.But I am really not sure what the problem is.Can someone explain the process of events that can occur that the current limit of the meter functions properly but the voltage is stuck at 0.5V output ? It is on last page of manual. I have alot of trouble understanding that circuit. The one with the light bulb. If I measure it, the current is spot on and stable. And I either checked or replaced every single transistor in the circuit. They all read rational values on DMM tests. I even bought stabistors and replaced those.https://xdevs.com/doc/HP_Agilent_Keysight/HP%206177C%2C%2081C%20Operating%20%26%20Service.pdfI am not clear if I can just isolate the voltage limit circuit completely and have just a current source? And the over shoot limit control, can I remove that too? I don't even care for these circuits, with how much grief this has given me, Ill sacrifice the DUT. Chances are I will set the voltage limit wrong or forget about it anyway, its kinda useless. Chances are if I am dealing with something precise and that has to kick on I will have to replace the DUT anyway.Will pulling the A5 jumper disable all the safety BS?

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2024, 02:56:43 am
content: Ok I started following the isolation procedures. It seems that the guard is not responcible.the voltage circuit still responds when I disconnect the diodes and resistor.When I reconned the over shoot circuit it still responds.I assume this means the voltage circuit might be the problem, since its supposed to go unresponcive.I just wish that I can disconnect the brain of the person who wrote the procedure with things like "disconnect the connector of Q6". God I hate doing that.

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2024, 04:22:15 am
content: And a question, is the 6177C a better bet? Because I think I had it with this one.I think it is the charred board or something, because these problems are nonsense. I think I should just try a C model.I think the build quality of the A is bullshit. IMO its ridiculously bad to work on.ALl the god damn test points are off. I fixed like 10 different things from this HP style, I dunno WTF it is with it. I have a feeling they did some subcontracting or something because why the hell does this one not have a PCB mounted transformer. They got fancy with the transformer but the wiring is crap. I really don't like this machine. I need to check the board but I am just not gonna take it out again after soldering all those perimeter wires. it feels like a monsterous troll.I looked through the RevC model manual and its like way better too. The A manual reminds me of my work when I am doing a proposal for work, its like flow of consciousness. I wanna call this thing a mock up for a board of directors.But I am angry because usually I learn something at least, I don't think I learned anything here. I just remain confused. I suppose I should methodically go through the manual isolating the parts and shorting stuff etc.

author: enut11
author_rank: Super Contributor
timestamp: August 01, 2024, 05:33:16 am
content: Hi@coppercone2. You have more patience than me! I had an "A" model and tried some repairs. It was not much fun. Sold it and bought a "C" model and am much happier.I do use the voltage control and think that it is handy, usually set to 10-15v. Don't forget the CC is at the compliance voltage when you connect the DUT.I also learnt not to leave the supply on but unconnected for long periods of time as it sinks any unused current internally leading to a largish temperature rise. A fan blowing on the heatsink helps.enut11

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2024, 10:05:42 pm
content: Yo when I took it apart I thought I gotta replace everything I can because I am not gonna take that board out again.Right now I am replacing parts from top using careful measurement and top soldering + peeking into the crack on the bottom (I forgot two 2n2907a transistors).I wish I took a picture of the bottom of the PCB though.The most glaring thing right now is that I see the 18V rail is low. It makes me want to replace those op-amps in the socket. I don't trust them. I think if that rail diode died, maybe both of them got fried.I replaced every diode, carbon composite resistor(with metal oxide), electrolytic and most of the transistors. That's the only reason I did not throw it into the trash. That was ALOT of work. But I thought there is NO WAY I will be able to normally repair this thing (leaving as many original parts as possible).But here is the kicker: when I remove the op-amps, the 18V rail is 12V. When I put them in it goes to 13V!It makes me think there must be another component that is causing trouble, and the op-amps are partially 'opening' the short circuit. But I swear every transistor looks OK. I measured everything on the PCB with a diode tester like 3 times. Its infuriating.Like I went through the damn thing with a check list on the diode drops. There is no god damn short or open. Its doing something asinine.I wonder if the 0.4 volts is a clue of some kind. It suspicious like a diode being in reverse. but it looks all good.and I got mad and killed it because my finger slippedIt really tells me something when the rev C version has a whole nother board segment.

author: coppercone2
author_rank: Super Contributor
timestamp: August 01, 2024, 10:30:49 pm
content: I got a question for you,is the C revision horrible with the PCB where it is basically sewn into the chassis with tons of solder wires around the perimeter? Or did they maybe use some connectors and make it possible to remove it from the chassis without a heroic effort?The picture I found shows 2 connectors and a card edge... is this accurate?Because, I don't have that much of a problem with the circuit, its just the mechanical design utterly disgusts me. I know who made it. Its one of Andrei's experiments. I heard there might be more of them in the sewers of Hollywood, CA.

author: enut11
author_rank: Super Contributor
timestamp: August 02, 2024, 06:07:05 am
content: Hi @coppercone2The 6177C is a much better design with plug in cable looms. I also modified mine with a 500uA range. The supply is good enough for uA stability.The 500uA mod is described in the Forum somewhere. It needs a new range switch and a precise 1.8K resistor.

author: enut11
author_rank: Super Contributor
timestamp: August 02, 2024, 06:49:26 am
content: Current sources can produce a lot of heat, especially if they also have high compliance voltages. The HP 6177C can work up to 50v/500mA, this means up to 25W of heat!I recently bought an IR imaging add-on for my mobile phone and took a pic of the 6177 top PCB. Note some temps are well over 50C! The transformer is at the top RHS. Middle right are the driver transistors and lower center is one very hot resistor.This is why I recommend a fan blowing over the rear heat-sink as a minimum.enut11

author: coppercone2
author_rank: Super Contributor
timestamp: August 02, 2024, 01:47:28 pm
content: the 500uA range is interesting to me.Maybe something good can come out of this fail, the C PCB does not seem to present any particular problems

author: coppercone2
author_rank: Super Contributor
timestamp: November 02, 2024, 10:00:45 am
content: I rewired this fucking thing, the crimp tool should be here soon to redo all those crimps. I used slightly thinner PTFE wire of very many colors. I investigated replacing it with some other connector but it was not worth the hassle compared to just buying a new crimp tool, and its the right thing to do because I can do board swaps in the future for trouble shooting, since I now own 2.It only took me like forever to replace all that old wiring. this thing does some really strange stuff when the wiring goes bad, it tricked me a few times with strange behavior. One of those things where even if you measure super carefully and at different mechanical directions it still does not seem to register as a open or high Z. The output voltage is high (100V), so I am scared to do the usual method of finding these problems, aka poking at stuff randomly unless its the mains. Normally HP is really good about where the HV is (though you need to add heat shrink and avoid certain parts. But when the machine itself does HV as normal function the complicated point to point soldering really starts to piss me off. Some how I managed to desolder everything without breaking any solder points.The potentiometer is scary inside but its servicable, one of them had a shady pot. I replaced it but later realized it DOES actually open up and does come back together but to me its a miracle that their design works lol.the next high voltage wired like this thing I get is gonna get all its wires replaced during repair, its not worth trying to find the issueI bet the original one that ended up getting dismantled (A version) also had this wire fault, that was not showing up on point to point measurements for whatever reason,, but I don't think I could stomach rewiring that attrocitynow I want to rewire all my old HP stuff lol. a few people here must have started regurgitating bile after reading that.replace all front panel wiring

author: m k
author_rank: Super Contributor
timestamp: November 02, 2024, 01:20:57 pm
content: Quote from: coppercone2 on August 01, 2024, 10:05:42 pmCan't find 'A' version manual nor that 18V rail from 'B' or 'C' versions.'B' version has 11.8V regulated supply and 'C' has 12.4V.Both have also less than solid common.Maybe negative side is pulling common down.

author: factory
author_rank: Super Contributor
timestamp: November 02, 2024, 05:30:53 pm
content: Quote from: m k on November 02, 2024, 01:20:57 pm'A' version is from the mid 60s, it's going to be nothing like the B & C, think more Germanium parts and PNP instead of NPN. I couldn't find any free info either.David

author: coppercone2
author_rank: Super Contributor
timestamp: November 02, 2024, 06:26:42 pm
content: well don't worry about the A version my memory of the event is shoddy and the remains are in a jarstill not a bad buy for 2x octal opamp sockets, helipot metal cover, wire wound potentiometer and that interesting transformer that I can one day use for something more interestingI can test transistors using that socket that have warped leads without messing with them too much, i think they will fit easier into those sockets some way.If I took the time to install a whole bunch of single wire terminals and redid the wiring harness, maybe I would have had a easier time. But its just too much work for little rewardand beware, that one has wires soldered to both the top and the bottom of the PCB. it would not be easy to rewire it with connectors. You would either need to move everything top side, or make extra long wires so you can pull the board out and disconnect it (hardly ideal for the high performance device). and its not like rows of wires, they are sprinkled about in between parts etc. and its not much room on the bottom either.i would try to modify it if it was part of stranded space shipLike if your main project is a current source, then ok maybe its acceptable work load to wrangle with that. mine was a means to a few different ends and it was just starting to piss me off how I am hung up on a current source (I could make my own OKish one in a box for less effort then fixing theirs with good enough specs)also, beware the connectors, all three of mine had cracked connectors, while maybe there was only a few cracked connectors between the 10 other same form factor HP power supplies I have. I think the current sources stayed in active use longer, while the V power supplies got put on a shelf because their modern replacements were way more likely to go into service and replace them.

author: factory
author_rank: Super Contributor
timestamp: November 02, 2024, 06:56:27 pm
content: Did you keep the case sides & covers, or use them for something else?It would have been interesting to see some 'before' pictures too, the early stuff doesn't appear much on forums.Davis

author: coppercone2
author_rank: Super Contributor
timestamp: November 02, 2024, 07:29:27 pm
content: No they were all in crappy condition, I polish those side rails if its not too much work (takes a few hours on buffing wheel)I thought the A model was ever present.But this one is NOT the cool kind of HP chassis because you can't access the PCB from the bottom unless you take it out. The ones everyone knows and loves have access on both sides, making the diecast 'frame' a cool feature that aids in fast repair of stuff that is solder wired. When you put a aluminum plate in the middle it turns it stupid IMO. !when the bottom of the PCB is exposed, and its suspended in the frame, its awesome to work on it because you flip it over no worries for 90% of the solder joints. But when there is a plate in the middle, and you need to loosen about 10 screws half way to 'wedge' the circuit board out, it turns into a stupid feature that you 'wrangle' with.So IMO they lost every 'cool' feature of their die cast frame and instead made it into an annoying 'jingler' that feels like you are working with a metal chain of some sort.Now, if the 6177A was some how equipped with CAPTIVE screws on the frames that have the ability to be locked into place, that would make it better... but when you have that big aluminum sheet in the middle IMO 100% of the utility from the frame goes out the window. Its supposed to provide high access but it does not, and nothing fits or removes without losening basically everythingAlso the cool thing about most other HP frames, is that you can work on the unit side ways to access top and bottom of PCB. If its tightened well, so long it can't fall over on you, its great to work on. But if the plate is there, it loses this capability. With my other supplies, I had it side ways on the circuit board, so I can bob my head left or right to see both sides of PCB and probe, trace, etc, with schematic infront of me. That was a HUGE benefit.And while the C does have some cable harness, it still does have an annoying card edge connector where you need to losen everything up into the 'jingle' state, and it still has the plate, so you can't work on it side ways or flip it or access bottom of PCB easily.When you can put the unit on its side and access both side of PCB it feels like you are in a CAD program with 360 View IRL.

author: factory
author_rank: Super Contributor
timestamp: November 02, 2024, 07:53:23 pm
content: I could have made good use of those parts, that case size isn't exactly the most common...David

author: coppercone2
author_rank: Super Contributor
timestamp: November 02, 2024, 07:57:35 pm
content: Oh no, I have those and keep those because the frame might crack and its annoying to bond (big reinforcement plate).I mean the sheet metal stuff was in foul condition. Its plastic coated or something and I believe its a measure of safety (isolation), so if thats damaged I get rid of it. I don't think paint is up to the 'spec' it needs, given how close the conductors are to the chassis.The cast HP side plates I keep, it only takes 1 drop to fracture that sometimes.On some unit the side plate is within 1cm of the transformer main wiring. If that cracks off, its easy to get a hot panel. So if the insulation on any of those panels is missing I don't use them. The ground is a bit shady to trust that much.I polish those panel too, not just the rails, but rails you can sand down, the panel can only take a gentle buffing with car paint polishing compounds

author: coppercone2
author_rank: Super Contributor
timestamp: November 02, 2024, 08:39:29 pm
content: actually I can't renember if i threw it out, it might be under something, i can't seem to find the castingi was wondering if the a one is compatible with the c onethe mod4 crimper is a pleasure to use, but it does not have a loader thing, so you need to load it with tweezers first

author: factory
author_rank: Super Contributor
timestamp: November 02, 2024, 10:43:11 pm
content: It was the side cover panels that I'm missing (exactly what is not in the picture), they usually clean up fine with foam cleaner & some shoe brushes I have. The size is unique to these narrow cases.The cast alloy frame should be the same on the A & C.David

author: coppercone2
author_rank: Super Contributor
timestamp: November 02, 2024, 11:22:40 pm
content: someone should 3d model them so you can just get it cnc machined from aircraft aluminum and forget about iti know people would pay. i probobly wouldwhen I had to fix the one on my RF amp (or was it function generator?) I thought I would pay like 300$ for that part if someone had itBut I ended up doing a splint with a piece of mild steel and 5 screws.getting that part is similar stress relief to going through 20 bottles of alcoholI did find them but I know i will curse myself in a few years if I do sell it because a good current source... might be forever. And it could get adapted to other frame with some work

author: coppercone2
author_rank: Super Contributor
timestamp: November 02, 2024, 11:44:28 pm
content: where am i?

author: factory
author_rank: Super Contributor
timestamp: November 03, 2024, 12:50:03 pm
content: Quote from: coppercone2 on November 02, 2024, 11:22:40 pmThe 2 side panel covers are for a counter, which I imported from the USA, they don't exist in the UK any more, sellers destroy everything for a few glass parts and throw the rest in the trash, before listing them on e$pay, they don't care if it's the last one in the UK.Also I've not found anything useless that uses that narrow case and can't justify scrapping usable or working TE to take the parts. It's not the only counter I have with missing covers, I've found some of the counters use unique sized top/bottom covers too.If you want to keep them for something else that isn't a problem, just let me know if you change your mind, doesn't matter if that is years later, I'm quite patient.The cracked frame I have is also one of the small amplifiers, though mine is the pulse version, very similar looking to the RF amp. Maybe I can straighten & join that one.Quote from: coppercone2 on November 02, 2024, 11:44:28 pmUSA, this is not really an issue for me, I have ways to get stuff that ePay sellers don't want to send international.Re: the wiring one HP current sources, I used to own a late 6186C (300V 100mA), the main PCB was hardwired in that, no connectors for unknown reasons, that one I sold some years ago, which I now regret.But I solved that by buying a cheap & poor condition 6186B to repair, it's the one with the messy main board, which I posted some pictures of in your transistor tester thread, all those random unmarked transistors & other added parts are now removed.To make this one even better, they lost the boron nitride transistor insulators & put more heatsinks on the back of the unit, which are live at high voltages.I don't think they make those insulators anymore, but maybe others in ceramic are available, I've not looked yet.I noted you asking about the TO-39 heatsinks for your 6177B/C? Seems the 6186C used one, but the 6186B doesn't need one, no idea why.David

author: coppercone2
author_rank: Super Contributor
timestamp: November 14, 2024, 01:51:15 am
content: I finally got around to trying to salvage the rest of the hardware off the remains of the PCB from the scrapped one's PCB (originally I only removed some of the parts for transplanting, aka saved my metal oxide resistors I added), now that I have two working 81'sIt turns out those things on the back for the screw terminals (solder down through hole bent plates with hole) were somewhat defective, just like the bus wire that I found that was cracked in half. They are on both sides of the PCB and conform around the plastic bit with the threaded inserts.I desoldered them and some that I tested basically snapped from a minor amount of deflection, while some of the other ones survived like 4x more bending. It was very brittle.I was sure that part would be a keeper (it can be used as a solder point for a bolt).I guess the same thing that caused that copper wire "jumper" arch to crack in half, also effected the screw terminal connectors.I have seen things like that for soldering to bolts break before, but usually their pathetic sheet metal stampings, these are like pretty beefy, but clearly its not a guarantee to just make it fatI wonder if its because of thermal cycles, or some kind of corrosion.

author: factory
author_rank: Super Contributor
timestamp: November 14, 2024, 06:18:37 pm
content: If it's anything like the 6186B, the rear terminal blocks are not supported in any way, other than the solder joints. Not surprized they crack, using a screwdriver will press against them, bending them and repeated use will cause them to fatigue, one has been replaced with a bodge wire in mine (not by me).I've found some possible alternate solder links to replace the broken ones (made by Cinch), but haven't ordered them yet so can't confirm they will be long enough, the screws are #5 40TPI UNC, there are some Cinch 140 series jumper links I intended to order too.David

author: coppercone2
author_rank: Super Contributor
timestamp: November 14, 2024, 08:52:19 pm
content: I thought they were thick enough to not have to worry about that, its at least 3 times as thick as the usual brass hardwareI thought it might be chemical because the nice looking jumper wire cracked too, and its not really doing anything related to threads.

author: factory
author_rank: Super Contributor
timestamp: November 14, 2024, 09:12:49 pm
content: Brass parts are known to go brittle with age too, but I've seen this in much older stuff, de-zincification is a thing too.David