BK precision 1730 Problem output is 50 volts - Page 1
Forum section: electronics / general

author: cowboy303
author_rank: Regular Contributor
timestamp: July 01, 2012, 03:50:59 pm
content: Hey guys.OK I just got this BK precision 1730 power supply for next to nothing. I plugged it in and the voltage with know load was 50 volts (TESTED). turningthe knobs didn't change anything. I was hoping that there is a zener diode or something that very commonly goes bad that I don't know of. But maybe one of you do. I don't want to fill this post with needless talk and make you guys read it so Please feel free to ask questions. I can check voltages, resister values, capacitor values, I can take stuff off the board and test it off the board. If it helps you I'll do my best to get it for you.Thank you very much.

author: tom66
author_rank: Super Contributor
timestamp: July 01, 2012, 05:19:47 pm
content: Assuming it's a power supply this could be one of a few issues?- Failure in the control circuit- Failure in the readout displays (is output actually okay?) Does it use analog meters or digital ones?- Shorted power transistor

author: cowboy303
author_rank: Regular Contributor
timestamp: July 01, 2012, 05:58:10 pm
content: Quoteyes I should have said that in my first postQuoteIt's analog and I tested it with a fluke and a extech multimeter.QuoteThat could be it. It has two 2n3055 transistors the collectors are connected together and is at 50.5 volts the bases are connected together and are at 50.2 volts and the emitters each go throw a resistor then connect together and are at 51 voltswhich does not make much sense to me.QuoteI've been looking but didn't see anything yet.

author: SeanB
author_rank: Super Contributor
timestamp: July 01, 2012, 06:06:25 pm
content: Disconnect the base connection and the collector connection and check the transistors are not shorted. Most likely they are either shorted or are leaky. If they are ok then power it on and check the voltage on the disconnected leads and what is on the output.

author: tom66
author_rank: Super Contributor
timestamp: July 01, 2012, 06:06:58 pm
content: Definitely sounds shorted to me. Can you post some pictures? With the PSU off, test the resistance from collector to emitter. It should be very high. Anything less than about 10 ohms indicates a potential short.

author: cowboy303
author_rank: Regular Contributor
timestamp: July 01, 2012, 06:22:28 pm
content: Quote from: SeanB on July 01, 2012, 06:06:25 pmJust tried disconnecting the base and it's still above 35 volt when pulling .5 amps I'll try replacing the transistors and will be back with you in about 20 minutes.Thank you so much

author: SeanB
author_rank: Super Contributor
timestamp: July 01, 2012, 06:31:11 pm
content: One or more are rather leaky........... Replace both, and preferably with something better voltage wise. I would suggest a pair of 2N3773 as a better replacement. Similar current ratings and gain, but lower leakage at the voltage in this supply, and overall a higher Vce0.

author: cowboy303
author_rank: Regular Contributor
timestamp: July 01, 2012, 08:21:20 pm
content: OK I unsoldered the two 2n3055 transistors and before putting new ones back in I turned it on and the voltage was still highso I checked for anything that could be giving it power and the only thing left is the sense lines. what I do see is a to-92 transistor model 2n5818 and some zener diodes that looked to be fried I'll need to get replacement for.

author: cowboy303
author_rank: Regular Contributor
timestamp: July 13, 2012, 01:50:25 am
content: Sorry to bring this one up again but.I was wondering if there was a place I could find the circuit diagram for the BK precision 1730 (rev H made in 1996) online I've been looking but can't find anything. I've been trying to follow traces and I think it would go abit faster if i had the circuit diagram to look at.Thanks.

author: MikeK
author_rank: Super Contributor
timestamp: July 13, 2012, 02:36:09 pm
content: You might email BK. They were nice enough to send me a PDF of the schematic for my discontinued 1670.

author: cowboy303
author_rank: Regular Contributor
timestamp: July 15, 2012, 01:15:31 am
content: Quote from: MikeK on July 13, 2012, 02:36:09 pmGood Idea I will give it a shot.