Repair help - Power Supply GW model GPC-3020, Master Channel not working

[MakerJeff]

I have a used 3 channel power supply (Goodwill  Instruments GW model GPC-3020
) from craigslist that I want to get working to start an electronics workbench in my home workshop.   

The slave side and fixed 5v appear to work in independent mode.   But the master side is dead in independent mode.   In parallel mode the master side knobs and meter function.  Nothing in series mode.

I popped off the cover but couldn’t see any obvious issues.  I couldn’t find a service manual or schematic for the machine online. 

I did find the front panel wasn’t installed correctly and a signal line was pinched by the case, so someone previously had been tinkering with it. 

Any ideas what the problem may be?     Fuses all appear intact.  No loose connectors.  No burns on the traces or components. The master side relay doesn’t switch, I can hear the slave side working. 

I don’t have the confidence to start probing around without some guidance.

[SpecialK]

Here's an owners manual with a block diagram that might be helpful.

https://makerspace.jhu.edu/wp-content/uploads/2018/01/manual.pdf

[tpowell1830]

This PSU is also labeled as PS280 from Tektronix, with the difference being that the readouts are 7 segment on the PS280. I have the PDF schematic. PM me and I will send it to you.

Also see the third comment reply on video.



Hope this helps...