Lab supply repair help - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th January 2010, 12:28 PM   #1
shzmm is offline shzmm  Germany
diyAudio Member
 
Join Date: Jul 2008
Default Lab supply repair help

Hello,
I am trying to repair a laboratory power supply with 2x15V output with adjustable current of 200ma-5A. It's a commercial unit from the late 70's.
The problem is one side is not working. The transformer is fine, I get 23VDC after the diode bridge. I first replaced all the electrolytics thinking that could be the source of the trouble but no luck. Then I swapped the ICs but the problem persists.
The supplies use an opamp UA723CN, transistors bc2378, bc 161 and power transistor 2n3772.
My guess is a faulty transistor but I can't find anything on the bc2378. I have to admit my knowledge of how these large power supplies function is very limited.
Any help would be appreciated.
  Reply With Quote
Old 9th January 2010, 04:33 AM   #2
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
Any chance it is a BC237B instead of a BC2378?

Regardless of the circuit, transistors are transistors. Pull them and test them with your diode test function on your meter. If you find a dead one, replace it. If the mystery part seems to check like a transistor, it is probably OK.

Verify the resistors in the circuit, especially if you see any fractional ohm resistors like 0.1 ohm or something. An open current sense resistor could shut down the supply.

Look at a data sheet for the 723. No what appears on its pins? How are its needs not being satisfied?

And of course, what is the make and model of your supply?
  Reply With Quote
Old 9th January 2010, 05:37 PM   #3
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Good news: If the two sides are identical, then you should be able to compare measurements between corresponding points in them, to help find the problem(s).

For example, (with power disconnected) measure the resistance in both directions across each pair of transistor pins on each side. If everything is identical, then it's probably not a transistor. If there is a difference, then it's probably either a transistor or something nearby.
  Reply With Quote
Old 9th January 2010, 07:49 PM   #4
shzmm is offline shzmm  Germany
diyAudio Member
 
Join Date: Jul 2008
Hello and thank you for the replies. I think the BC161 is the culprit. I'll have to verify it Monday when I can get a new part.
And yes you were correct it was a BC237B, my eyes just aren't what they used to be!
For what it's worth the make and model of the supply is a Dynamic NG-1525 made in W.Germany. I think it has around 30 years of German dust inside.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Lab Power Supply Nikon1975 Tubes / Valves 2 11th December 2009 10:52 AM
Lab Power Supply Current Limiting Q Wynand Equipment & Tools 4 27th September 2005 10:44 PM
GC with lab supply Eric Weitzman Chip Amps 1 5th March 2005 03:32 PM
diy lab supply jazz Solid State 9 20th January 2005 09:28 PM
Lab Power Supply for Glass Audio TerryKing Tubes / Valves 0 28th April 2004 11:59 AM


New To Site? Need Help?

All times are GMT. The time now is 09:14 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2