Delta Elektronika 0-15V 15A +5V 13A PSU

Sometime ago I received 2 Delta elektronica power supply’s from a colleague. One is 0-15V  15A and the other one is a fixed voltage of 5V at 13A max. The first one is defective, and the second one brand new.

So lets start with the investigation on what is wrong.

The output voltage of the power supply is 0.5V. I know that sometimes on these power supply’s the crow bar fails, so I disabled this circuit and still 0.5V max on the output. In the mean time I received the schematics, this helps a bit in the search. This way I could check the switching signals, everything looked ok, but then I found that the voltage is being held back by the current limit. This should not happen since the potmeter is wide open. After some more searching this was caused by a broken zener diode.
Hurray it works now, well not exactly, it does make voltage, but almost no power. This was caused by an undocumented extension in the power supply, this connected 2 wires to unused pins in the connector. After shorting these the power supply worked. So I connected it to a 1R resistor, 15V 15A everything worked, switched it off, back on again. 0V on the output, hmm the zener is still good, wire connected. The during the analyses I noticed that the AC input of the power supply varied with the current limit. Hmm, so it is producing power. A resistance measurement on the output told me it was 0 Ohm, even with no load connected. Aha, this should not be. It should be a diode I thought, wrong. It was 1 of the elcaps that was a dead short. After replacing these everything worked again. However replacing these was also not straight forward, these antique form factors were not sold any more, so I pried the foots off and soldered the new caps to them. Not having the exact values I needed 4 caps on the footprint of 3.

After this the project got a whole lot easier. I removed the internal potmeters, soldered wires to the pads and installed external ones. Together with the other power supply and the meters it then looked like this:

Some more pictures:

The front plate:

I’m not happy with the labelling, so this needs to be changed later on. But for now the power supply is installed on the shelve with the rest of the equipment until I have time to update the labelling and know how I want to do it. If you have a good suggestion, please leave it in the comments below.

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