I was able to get hands on (read - get it for free) a
PeakTech DC power supply 6080. I was warned that it is broken, it works in general but it doesn't regulate or give a rated power anymore.
(I still decided to take it, as I am assembling my home small electronics lab and getting a free power supply that I might be able to get fixed seemed also a good project to learn troubleshooting and fixing.)
Downside is that I don't actually know what was done to it prior 'breaking'. Was the breakage caused by some high energy short circuit, or higher external voltage was present in the circuit while being connected... I don't know - what else could make a Linear DC power supply to go bad ?
I did some preliminary tests, switched it on and observed how it behaves.
1) I can change voltage with no load in constant voltage mode.
Its reading is off differently on different levels. When I get to about 4V on the LCD the multimeter shows me around 5V. When I turn to maximum position, LCD reads 15V and I measure 19.8V - again, no load.
1.1) The LCD reading fluctuates the last digit (so around 0.1V) when changing to a new value, but the multimeter reading is very stable.
2) Next I tested different loads.
With a simple LED, The Voltage regulation seems fine, same behaviour as for no load, reading on LCD is off, other than what measured with multimeter.
but f.i with DC motors, the PSU goes nuts.
I monitored the current with the multimeter. I could still tune the regulation (limit the current, and increase voltage for the loads) but the LCD readings are all over the shop.
Video of the behaviour [18MB].
perhaps someone already knows that this is some kind of a typical fault scenario on Linear PSUs or knows where could I start looking?Maybe a pass transistor is faulty or something in the output part of the circuitry is faulty...