EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: uliano on September 28, 2022, 11:57:36 am

Title: Power supply outputs random voltage
Post by: uliano on September 28, 2022, 11:57:36 am

Suddenly (after maybe some year of NON use) this old PSU got crazy

Often, but non always, more likely on channel 2, the voltage under load is less than programmed even if the drained current is far less than the preset limit.

I have no idea where to start looking to investigate this problem.

Some explicative pics.

(https://i.imgur.com/sKOVgVd.jpg)
(https://i.imgur.com/MDJ69dL.jpg)
(https://i.imgur.com/1DKUofM.jpg)
(https://i.imgur.com/StgP2Te.jpg)

Title: Re: Power supply outputs random votage
Post by: wraper on September 28, 2022, 12:12:22 pm

Your electronic load could be oscillating. Try adding say 1000uF cap to PSU output.

Title: Re: Power supply outputs random votage
Post by: uliano on September 28, 2022, 01:37:16 pm

I didn't think it was the case as the problem showed up with a real (and very small) load, however

(https://i.imgur.com/AK37zpm.jpg)

What is worst is that it doesn't even need a load

(https://i.imgur.com/AMHNQ1o.jpg)

Title: Re: Power supply outputs random voltage
Post by: Ice-Tea on September 28, 2022, 02:44:00 pm

If memory serves (and that's by no means a guarantee), the polarity protection diode on the outputs is a weak point in these supplies. Wouldn't hurt to check. YMMV, obviously, but it doesn't hurt to check...