Faulty ADI-8 Power Supply

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Dealanor

Member
Joined
Jan 27, 2006
Messages
5
Location
South Africa
A friend of mine's RME ADI-8 AE stopped working last week. After finding out he had to send it to Germany for repairs he brought it to me.

Now I'm trained in electronics, as I'm not really good at it (One of the reasons I changed my job). Strangely after years of being away from it, things seem to make more sense now, but I can figure out some basic things, but I'm still largely clueless.

I've spent the last week learning how switch mode PSUs work, after finding out that the PSU wasn't working.

I have managed to get the PSU roughly working, but the voltage is high. You are supposed to get 5V, 15V and -15V out and I'm getting 7V, 20V and -20V.

I'm assuming the feedback isn't working, and looking at the opto isolator on my scope, there isn't any activity there. I've replaced most of the semiconductors in that part of the circuit (except the zener).

What puzzles me is that the voltage on the reg input of the TL431 doesn't vary when I change the trimmer. It stays at around 2.1V. I've checked all the resistors around it and they all check out.

I've drawn that part of the circuit (hopefully without making an error), hoping someone has some sort of idea that might help me:

rme_smps_feedback.jpg


If anyone has any ideas that could help, it would be greatly appreciated.

Sven
 
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