derSammler wrote:

Was the PSU already dead when you got it, or was the system working and failed recently?

The system worked when I got it, but it failed when I touched the back panel of the tower to fasten the VGA cable.

Measurements so far:

blue = gnd
yellow = 5v
orange = 12v

The remaining pins are -12v and power good (conn.1) and power on (conn.2). Can't tell what is -12v and what is power good on conn.1, since I don't get any values. Might be my cheap multimeter, or my PSU isn't fully working and -12v is missing. In that case, it's most likely not needed to power the system anyway.

I'm speaking under correction, but I believe some older computers generated their own -5v, by using an existing -12v line.
So in case there's an 7905 (-5v) on the mainboard, someone might be able to trace down the -12v line.
Anyway, it's just an idea and no advice. Good luck with the repair, though!

Just set up my Schneider VGA AT System 70 CEG only to find out that the PSU is no longer working. Was still fine when I put the system into storage about a year ago. 😠 Have to disassemble it anyway to do some hardware changes, but repairing the PSU was not planned...

Interestingly, the Schneider Tower AT System 202, which is two years older (1988 vs. 1990) still works like a charm. Even with the now 31 year-old MFM hard disk. 🤣

Sorry to hear! 🙁
Not sure if I can help, but..

If you're going to repair the PSU, you may also have a look at the diodes (black with white ring or glass with red ring).
They should be located on the right side of the main PCB.. Replacing them with stronger 1N4007s should do, if memory serves.

Also watch out for the bigger caps and that big power mosfet.
Checking the voltage regulators may also help. Becareful with getting replacements, though.

The normal types (esp those. for the 5v line) that are commonly sold are rated 0.5 to 1.5 Watt only.
The parts installed are the more obscure 2 Watt types (though a 1.5W type may also do).

Cool looking 80s design 😀

I have 5 machines, but I did not have started them over the last 12 months. Perhaps my Systems have died too 🙁
I'll have to check that out soon.

The PSU only needs new caps. They have become dry and the control circuit doesn't come up due to this. Repair is planned, but currently I'm working on my Amiga 2000, so it may take a while.

btw. what are you doing on the a2000?

Just powered on my tower-at.

Is anyone have service manual for Schneider VGA AT system 40?
I'm loking for schematics of VGA I/O board. I suppose the same VGA I/O board used in Schneider 386 tower.