Troubleshooting/fixing Linear DC power supply PeakTech 6080 - Page 1
Forum section: electronics / repair

author: crypton
author_rank: Contributor
timestamp: May 06, 2018, 03:51:03 pm
content: I was able to get hands on (read - get it for free) aPeakTech 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.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...

author: crypton
author_rank: Contributor
timestamp: May 13, 2018, 11:35:11 am
content: I tried to take a look inside but didn't see anything too peculiar.Caps seemed good, but I don't have any ESR meter to know for sure.Only thing I noticed was a big black cap (50V, 4700uF) which seems to be the main filter cap. It has residue of liquid on top of it - not sure if that's supposed to be like that?I haven't seen this type of electrolytic before. The brown ones on the main board have vents but not on the black one. There's some very small holes on the top as well - like someone has poked them with a sharpie. Maybe it has blown to some extent ?When the unit was on, I didn't hear any noise though.Everything else seems ok. I don't think the main logic board has smth to do with the huge fluctuations on the LCD, but I haven't seen any spots of black smoke escape either.

author: crypton
author_rank: Contributor
timestamp: May 14, 2018, 07:43:27 pm
content: Dug a bit deeper. Fondled on an idea that maybe smth bad happened on the inputs.Noticed some components between input PCB and front panel. Decided to unscrew the terminal posts and took a look at the input boardBoom, a blown cap. 25V 330uF to be precise.Ok, great, but that doesn't tell me what was the extent of the damage.Anyway, I traced the connecting copper for the positive side of the capacitor - basically all the brown caps, also seen on the main board, are connected on the same rail.Even though all other caps seem fine, I will still replace all of them - just to be sure.1)Anyone might have a hint what type the orange-ish capacitor near the electrolytic is?Looks smth like thisOrange cap google searchIt says0. 1 K 100Seems that those orange-ish ones are polyester film capacitors ?The cap's positive connection also continued on the logic board, Some low value resistors seem a bit discolored (100and 0) more than others, so it may be that during a fault they suffered excess current and maybe got a bit roasted. Will make effort to replace them - again just to be sure.2)I am still not sure about the main big black cap - it seems isolated or separate from the input circuitry, so maybe that is still good ?