Electronics > Repair
HP 6177A repair (fixed)
coppercone2:
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 adventure
I 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.pdf
I 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?
coppercone2:
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.
coppercone2:
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.
enut11:
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
coppercone2:
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!
:scared:
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 slipped >:(
It really tells me something when the rev C version has a whole nother board segment.
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