Mega STE PSU question

[UnderTheRain]

Hi

Can anyone tell me if the PG signal from the mega ste psu is high or low for good. I'm too tired lol

The PSU is a 5341

psu.png (125.96 KiB) Viewed 843 times

power.png (114.55 KiB) Viewed 844 times

Thanks

Brian

[exxos]

With c23 being zero volts at turn on, Q3 will be off,Q4 will be turned on via R31, so PG will be low.

When C23 charges , Q3 will turn on, and turn off Q4, PG gets pulled high via R33.

R30,R32 divider give over voltage protection in that Q3 gets turned on, turning off Q4, PG gets pulled high via R33.

Its 5am, so someone check my workings out

[UnderTheRain]

Thanks dude

I should of been able to work it out but I was extremely tired. Above the bit I clipped is a 680uF cap c17 that exploded in my psu and r26 is burned out looking at the main mega board it seems to have a short 5v to gnd which will be fun for me to find. I'm not sure what else might be damaged on that part of the circuit I googled a lot of the diodes and bjt's (searching the specs just bring 1 result the actual bjt's that are there already) here and they seem to be somewhat in the unobtanium class. Looking at the main board the 8.2v reg on mine was crushed and the so was the cap next to it as well as two 2n3904's I think one next to the VME shield and one under it which it weird they must of been like that for a long time as well as one of the to-92's on the right. I changed the cap as it might of been destroyed and straightened all the to-92's. They're not the cause of the short though I don't think I'm sure I'll find it in the end. Weirdly my Mega STE is my fav ST so she's going to get fixed not matter what

Talking to Ian at mutant caterpillar he suggested I might try a Meanwell PSU instead (once I've found the short). I started looking for replacements for the diodes and bjt's in the psu and tbh a Meanwell looks like a much cheaper option and would probably be much more reliable. Meanwell do an RQ-85C (oops this is 15v lol lets look again its the b rq-85b) which has all the right current capacities at the right voltages (and it's pretty close in size) apart from the PG, does anyone have any experience with these psu's? any recommendations on an update/replacement for a Mega STE psu would be gratefully received.

Many Thanks

UTR

[Steve]

The Mega STe PSU is standard AT. Can still be found to buy in some places. Also I don't follow your logic of 'cheaper = more reliable'

[UnderTheRain]

It's not that it's cheaper is just 30 year newer tech