Kikusui PWC 0620 no voltage on 6V output

[WreckItRalph]

Hello all!

I've recently become an owner of a hand-me-down Kikusui PWC 0620 power supply with issues. The supply has a dual-polarity tracking +/- 20V supply which works fine and a 6V 3A variable supply which doesn't work at all. I've spent days testing components in-circuit but the only thing I was able to find was the + power supply pin on 1 of the op-amps wasn't connected (it was socketed by someone who's had a go at it in some distant past). I thought for sure this must be the problem but unfortunately no dice . I've contacted Kikusui to see if they could help out by providing a circuit diagram but was told this supply hasn't been supported in 30 years and I should buy a new model  Of course I'm here because I don't just buy new at the first sign of trouble  Has anyone repaired one of these supplies before? Do you possibly have a schematic or trouble-shooting document of some kind to help get this puppy going again? The user manual available from Kikusui is of no help and includes neither of these things Any help would be appreciated

[coromonadalix]

Did they provide you an service manual,  i bought a Kikusui PAD70-5   and they made me sign non disclosure agreement,  but i received the service manual ... i had a small failed part.

My psu is no longer supported 12 years ago ?  I strangely ressemble mine ........  if you could remove the top panel and take a couple of pictures, i need to see  whats around the transformer.

If you ask them again ??

[WreckItRalph]

No service manual, they replied it was too old and I should buy a new one I have many detailed pictures as I went along the way testing components, here's a shot from the side and one of the logic board.

[coromonadalix]

Well   its not made like mine
The operation manual : https://www.kikusui.co.jp/kiku_manuals/P/PWC0620_E.pdf           show a brief description of the working principles ...

A basic circuit is like this :

Or a detailed explanation : http://www.nutsvolts.com/magazine/article/op-amp-cookbook-part-4

You will have to reverse the circuit from the output jacks ...   find the regulator circuit / pass transistor / current limitter  etc ...   maybe do a hand draw sheet.

Where are you located in Canada ?  I'm in Quebec.

BUT
I see an floating red wire on the first photo  and a to-220 mica insulator with plastic screws,   did you opened the psu lke this    seems to be missing parts

[WreckItRalph]

I've been working the "dart board" technique thus far, doing a diode and ohms check on every component as I come across it, as well as continuity.

I'm in Pickering (near Toronto), Ontario, but I visit Quebec a few times a year, my gf is from Buckingham, like that area

Sharp eye with the TO-220 mica insulator and wire! No, that was an SCR that I removed just an hour before taking that picture. I completely remove some parts out of the circuit for testing because it's impossible to tell in circuit.. just too many odd results. I'm suspecting that SCR is shot now as well.. It's an ECG5465 and I'm getting 70 ohms both directions between gate and cathode (pins 1 and 3). Diode check shows short between those pins (both directions). That red wire flapping in the breeze is connected to the anode of that SCR. It's all soldered to a small circuit board then screwed with those plastic screws to the heatsink.

[alm]

Rather than measuring components out of circuit, I think that starting with in circuit measurements may be more fruitful. I expect there to be a > 6 V high current rail that feeds the pass transistor(s) and two rails feeding the op-amps that regulate the 6 V output. I would start by measuring if these are present. Next I would measure around the op-amps that do the voltage / current control. The voltage control one should be connected across the shunt in series with the output, and the current control op-amp across the output. If this is all fine, and the pass transistor is forward-biased, lastly I would check if the overvoltage protection (crowbar) is shorting the output.

[coromonadalix]

If you have an scr  it must be the crowbar protection circuit ........ it should not be a problem to make the 6v rail working.

If you were in Quebec, i could have poked in it to see whats wrong with it ?
 
Maybe My PAD schematics can be of some help, the biggest difference is my input transformer is scr controlled like an isolated huge buck boost converter, it limits the dissipated heat to the minimum ...  but the rest of the circuit must have some similarities, im sure of it ...

[WreckItRalph]

I measured in-circuit as well. Both + and - 12V rails and 6V references seem to be there.. everything I've checked thus far in-circuit seems to be ok, so I've taken to out of circuit testing anything that even remotely raises suspicion. Changed that SCR with an NTE5465, no difference so back to the drawing board, literally I'll have to cut open all that wonderful looming because there are too many same-color wires to simply guess at. Since someone has had a go at this thing before I would've liked to compare the components here with what used to be in here out of the factory but without schematic that's not possible. This unit came out of an electronics lab and it was worked on there.. chances are if anything had been replaced it would've been replaced with whatever happened to be at-hand, whether a perfect match or not, and if that's an issue I'll have a hard time figuring that out.

[WreckItRalph]

Fixed at last! 

Took me days of poking and testing, but I finally found the problem. A factory bodge wire went open on the logic board! The wire "looked" OK and I checked it mechanically several times and it seemed fine... BUT when I ohmed out the leads of the 2 components linked by it.. BINGO. I resoldered the bodge wire and the 6V supply is working fine at last 

If anyone else has this similar issue, here are some pictures and where this bodge is located.

[coromonadalix]

Glad you found out hte problems +1