Diagnostic help for my BK Precision 1672

[akcoder]

A while back I picked up a used BK Precision 1672 (dual 0-33v, 0-3a PSU, with a third fixed 5v). Sadly, the clown I purchased it from didn't bother to put the top piece of styrofoam in the box and the thing bounced around like a pin ball. And in the process sheered off all four pots, including the two push-pull pots on the master side (a pot with a built-in DPDT switch).

A friend and I did some temporary repairs (putting the push-pull pots back together, stringing wire from the pcb to the broken terminals of the pots) to verify that I wouldn't be pissing money away if I replaced the broken parts. The PSU worked great with the temporary repairs. After I replaced the broken pots with new parts though, the thing only worked for < 30 seconds. I turned the voltage dial through its range, and at almost the top, it crapped out (the lights are on, but the output voltage is 0v)

I verified I replaced the parts with the same values, the pots are 10k. I've checked the fuses on both the master and slave board and everything checks out. The fixed 5v works and outputs 5v as it should.

If I disconnect the communications wires between the primary and slave boards, everything works as it should. With them connected, I get 0v on both the primary and secondary.

Update
I think its the push-pull pots I got that caused the issue. While fiddling around with it, I slowly pushed in the put and noticed that the display flickered. When I slowly pulled it out, I heard a pop, and saw some magic smoke. Upon investigation, the back of transistor Q102 (C1815) is completely blown off. I pulled the master side PCB off and put the meter across the opposite poles of the switch and slowly pushed/pulled and there is definitely a spot there where the switch on the replacement push-pull pot bridges both sides together

So, now that I think that I know what the issue is, does anyone know where I can get a good 10k push-pull pot from? The ones I ordered came from fleaBay because that was the only source I could find at the time. The ones I need are pins, not lugs.

Thanks,
Dan

[saturation]

Interesting to see much through hole parts in a current PSU from BK.

Push-pull pots abound on google.  However if its a quality version I know Bourns still makes them, but it may not be your form factor.  They remain from radio, audio, and guitar repair places.

http://www.mouser.com/ProductDetail/Bourns/54AAD-C28-B13-P50L/?qs=sGAEpiMZZMtC25l1F4XBU3K722tofIu5TQfbq%2fDN9rk%3d

[tom66]

Probably because it's not a BK design. Any clue on the OEM?

[casinada]

Usually the Printed circuit board would give you a clue on the OEM manufacturer. Look for the board number. I found them that way on some Tektronix and Amrel power supplies.
 

[akcoder]

Interesting to see much through hole parts in a current PSU from BK.

Push-pull pots abound on google.  However if its a quality version I know Bourns still makes them, but it may not be your form factor.  They remain from radio, audio, and guitar repair places.

http://www.mouser.com/ProductDetail/Bourns/54AAD-C28-B13-P50L/?qs=sGAEpiMZZMtC25l1F4XBU3K722tofIu5TQfbq%2fDN9rk%3d

Yeah, I found those yesterday. The perfect item would be higher quality version of these fleaBay specials I put in which bridge the poles, with pins instead of lugs.

-dan

[akcoder]

Usually the Printed circuit board would give you a clue on the OEM manufacturer. Look for the board number. I found them that way on some Tektronix and Amrel power supplies.
 

The only numbers on the boards are PWB-331J on the master board, and PWB-332J on the slave board. A search of the interwebs returns nothing for either of these numbers :/

-dan

[akcoder]

Probably because it's not a BK design. Any clue on the OEM?

I have no clue on the OEM for these. The only markings on the board are PWB-331J on the master, and PWB-332J on the slave. I can find no information on either of these boards online.

-dan

[akcoder]

Interesting to see much through hole parts in a current PSU from BK.

The board is very well laid out. The test points are all clearly marked, and the emitter, base and collector are marked for all the transistors.

-dan

[saturation]

You can't go wrong with BK, they've been in business since the 1970s, I've used their stuff off/on since then and never had a problem with build quality.  The only issue, is it bang for buck for what it does?  You can get a lot of used decades old BK stuff off eBay to show its quality does endure.  Its products are definitely cut above China branded items for the same function, but less than GW Instek [ and as expected, GW charges even more!]

Interesting to see much through hole parts in a current PSU from BK.

The board is very well laid out. The test points are all clearly marked, and the emitter, base and collector are marked for all the transistors.

-dan

[Bryan]

Hmm, is it just me or is R202, left of the red circle missing solder on the bottom leg?

[akcoder]

Hmm, is it just me or is R202, left of the red circle missing solder on the bottom leg?

Yeah, the fill on the joint is less than optimal, but its fine on the bottom side. I'll touch it up when I'm in there next!

-dan