Tektronix PS280 power supply slave voltage stuck

Thread Starter

Dahoffman85

Joined Jan 25, 2020
2
Hello everyone, I recently acquired a Tek PS280 power supply. It is a 3 channel PS having (2) 0-30v, 0-2a channels and (1) 5v, 3a fixed channel and 3 modes (independent, series, and parallel). Below is my issue followed by everything I’ve tried to diagnose and fix the issue it is having. Thanks in advance for your input!

When I first got the PS I began to test everything and here is what I found:
Set to independent mode:
Channel 3 (5v fixed) works fine, tested on the DMM and it’s putting out a constant steady 5v and 3a no issues (no display)
Channel 1 (Master) works fine, tested on the DMM and it’s putting out 0-31.55v, and 0-2a (display aligns with DMM)
Channel 2 (Slave) HAS ISSUES, display shows 0v and shows 0-2a, tested with DMM and 0-2a is correct and working fine, however voltage is stuck at a constant 18 volts
Set to series mode:
Channel 1 still works fine as above
Channel 2 still has issues above
Series works fine as tested with DMM I am receiving 49.55 volts from both channels (31.55 plus 18)
Set to parallel mode:
Channel 1 still works fine as above
Channel 2 now works fine as it’s controlled by Channel 1. Tested with DMM I get 0-30v, 2a (display still shows 0)
Parallel works fine as both channels workin unison, being controlled by Channel 1, and putting out 4 amps across both channels

Here is what I have checked:
Being that the slave side worked fine in parallel, being controlled by the master potentiometer, I though the slave pot might be bad. I tested it (along with the 3 others to be safe) and all 4 worked fine. I next checked all fuses on both master and slave and all were in perfect condition. Finally I checked the (3) power transistors controlling each rail of power and they all are in fine working condition as well. Also just FYI I checked all circuit boards and found not bad or loose connections and no burned out parts or shorted wires. One more thing of note is that there is only 1 power transistor per channel and no pass transistors in between a low or high voltage control but on the master side I can hear a clicking when voltage is activated from 0v and again at 15v. I hear no clicking at all on the slave side, even when it’s working fine in parallel.

Please let me know if you can think of what may be causing this issue, thank you!
 

Thread Starter

Dahoffman85

Joined Jan 25, 2020
2
I’ve been studying that manual for over a week now. While there are multiple issues with it and the schematics the big bummer is there were 3 different versions of this power supply during its production and the only manual you can find online is for the first version with separate master and slave circuit boards as well as separate fuse boards and (2) power transistors per channel. I have the 3rd version which condensed everything down to one main circuit board and only (1) power transistor per channel. Although I’m slowly making sense of it and now have a giant map of of circuitry I’m painstakingly connecting the dots with. Just trying to get an outside perspective as I know I can get very narrow minded when I focus so much time and effort into a project. Pretty soon I have to take a step back and get my mind fresh again.
 
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