Diagnostic help for my BK Precision 1672 - Page 1
Forum section: electronics / general

author: akcoder
author_rank: Contributor
timestamp: October 15, 2012, 05:21:39 am
content: 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.UpdateI 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 togetherSo, 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

author: saturation
author_rank: Super Contributor
timestamp: October 15, 2012, 07:03:27 pm
content: 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

author: tom66
author_rank: Super Contributor
timestamp: October 15, 2012, 07:07:31 pm
content: Probably because it's not a BK design. Any clue on the OEM?

author: casinada
author_rank: Frequent Contributor
timestamp: October 15, 2012, 08:03:49 pm
content: 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.

author: akcoder
author_rank: Contributor
timestamp: October 16, 2012, 02:52:09 am
content: Quote from: saturation on October 15, 2012, 07:03:27 pmYeah, I found those yesterday. The perfect item would behigher quality version of these fleaBay specialsI put in which bridge the poles, with pins instead of lugs.-dan

author: akcoder
author_rank: Contributor
timestamp: October 16, 2012, 02:57:10 am
content: Quote from: casinada on October 15, 2012, 08:03:49 pmThe 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

author: akcoder
author_rank: Contributor
timestamp: October 16, 2012, 02:59:43 am
content: Quote from: tom66 on October 15, 2012, 07:07:31 pmI 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

author: akcoder
author_rank: Contributor
timestamp: October 16, 2012, 03:10:23 am
content: Quote from: saturation on October 15, 2012, 07:03:27 pmThe 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

author: saturation
author_rank: Super Contributor
timestamp: October 17, 2012, 05:46:35 pm
content: 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!]Quote from: akcoder on October 16, 2012, 03:10:23 am

author: Bryan
author_rank: Frequent Contributor
timestamp: June 25, 2013, 08:30:36 am
content: Hmm, is it just me or is R202, left of the red circle missing solder on the bottom leg?

author: akcoder
author_rank: Contributor
timestamp: June 25, 2013, 06:23:19 pm
content: Quote from: Bryan on June 25, 2013, 08:30:36 amYeah, 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