Metcal PS5000, trying to repair (Need info on C43)

[dfnr2]

Hello,

I picked up a nonworking Metcal PS5000 on Ebay.  It was advertised as "Untested, For Parts or Repair".  I opened it up and found the two mains fuses blown, and also Q3 was dead, shorted.  I couldn't find any other obviously bad semiconductors so I replaced the fuses and Q3, hoping to scope it out from there.  Right away on powering up, There were sparks and smoke, and C34, the cap close behind Q3, blew up, shorting out, and blowing the mains fuses again.  Q3 and other semiconductors still look OK, and I'm wondering if a borderline C34 might have been the issue.

I can't find online schematics, so I'm wondering if anyone here might have access to a unit to be able to tell me the type and value for C34.

Many thanks,

Dave

[thm_w]

Photo?
What part did you replace Q3 with, identical?

https://www.eevblog.com/forum/reviews/metcal-mx-ps5000-issue/
https://andydoz.blogspot.com/2017/10/metcal-mx-ps5000-repair.html

[dfnr2]

Q3 is a FQPF13N50CF MOSFET.  I replaced it with the same.

[dfnr2]

I made a mistake, it's C43, not C34.

It turns out there was writing on the side of the cap that wasn't blown out.  It was just too faint to see without strong lighting and a magnifier (or a polarized lense).

It's thick and blue, suggesting a safety cap.  The markings are B 332K 1KV. 

I ordered a couple of 3300pf 10% 1KV safety caps, TDK series CK45, which seems to be a match, and will see if that works.  All the big transistors and diodes seem to be OK still, including the just-replaced Q3.

Perhaps C43 failed and blew the fuse before outright exploding, and once I replaced the fuses, it exploded.

I am hoping to get to the point where it's not blowing fuses, so I can actually start troubleshooting.

[dfnr2]

Installed the replacement and fuses, and now there's no explosion, but no 24V or 48V out.  Now, I can start to map out the circuit and start debugging.

Pin 8 (RAMP) of the FAN4800 PWM controller is discolored, and the PWM controller would be a good place to start investigating, although that pin shouldn't be at risk except in the case of a catastrophic chip failure.