Issue with asp34-2 ATARI MEGA ST4

[sviru]

Yes, I had the same issue, my mega fan was basically a dead short, replaced it with a noktua 40mm fan (it fit perfectly) system up and running
.

I got a meanwell 65 as it also has -12 for the STGA.

Oh I have 2 et4000 1 meg VGA isa cards and just got a mach 32 so if anyone needs one just ask.

Nope - it was not a fan. I think I will buy a new psu.

[frank.lukas]

Check L2 and replace D4 and D5 for new ones ...

[sviru]

Check L2 and replace D4 and D5 for new ones ...

I will. Is there a chance that something is bad on the other side of the transformer? Not on the obvious 12v part of the circuit?

[atari030]

Pretty sure I have two of these with the same symptoms. Both recapped both have voltage drop under load. Test perfectly off the board. I had spare PSU's so never pursued it, I might have another look now I have a few Amiga's out of the way.

[sviru]

Pretty sure I have two of these with the same symptoms. Both recapped both have voltage drop under load. Test perfectly off the board. I had spare PSU's so never pursued it, I might have another look now I have a few Amiga's out of the way.

That would be great. I have checked all caps even the small 1uf tantalum cap. It looks like there is not enough juice under load since it drops quite a lot. Maybe the optocoupler? But I wonder if my 5V is OK could it be possible that optocoupler is still faulty. My knowledge on switched-mode power supplies is not that great.

[rubber_jonnie]

Pretty sure I have two of these with the same symptoms. Both recapped both have voltage drop under load. Test perfectly off the board. I had spare PSU's so never pursued it, I might have another look now I have a few Amiga's out of the way.

That would be great. I have checked all caps even the small 1uf tantalum cap. It looks like there is not enough juice under load since it drops quite a lot. Maybe the optocoupler? But I wonder if my 5V is OK could it be possible that optocoupler is still faulty. My knowledge on switched-mode power supplies is not that great.

I'm pretty sure the opto-coupler only gives feedback for 5v, 12v is unregulated.

If you've recapped the PSU then D4, D5 and L2 would be potential candidates. I'm fairly sure, looking in retrospect, if Q1 and Q2 were bad, you'd get nothing at all.