Powermac G3 PSU Repair

[Bentendo64]

Hello everyone. A coworker asked if I could look at the power supply for his G3 tower.

Reported symptoms to me: his mother was using it, and suddenly there was a pop sound, smoke, and the machine shut off. Coworker found a blown fuse and replaced it. Fuse was blown immediately upon application of power from the wall.

I started with the small board that perhaps supplies STBY power? For the sake of this discussion, I'll call this the STBY power board, until otherwise corrected. I've found the drive transistor (IRFBE30) shorted and a resistor next to it fried. The brown wire from this converter goes to a place on the main PCB labelled "Vcc". This pretty much has a dead short to ground, which explains the shorted drive transistor.

I removed the vertical board int he middle of the main PCB, and found this is the source of the short. I found Q201 (MPS2222) shorted, and found its output goes to IC201 pin 16. Pins 15 and 16 of IC201 look a little like they got hot, see pic:


Pin 16 definitely has serious DC leakage to ground, on the order of 10 ohm or less, and has similar leakage to pin 15. I presume this is atypical, but I didn't take the chip out of circuit. I did remove caps that could have been shorted, however.
I can't seem to find the datasheet or reliable source of this chip. Am I screwed?
Does anyone know these power supplies? It seems this may be the end of the line as far as I can diagnose this, and may start looking into an ATX conversion.

 

[GiGaBiTe]

That TLS1207AN chip has a crack right down the middle of it, it's toast. Probably exploded internally, just not with enough force to blow the package apart. Even assuming you could source that chip, there are other serious problems with that supply. I'd wager that most of the mosfets/transistors are blown or damaged, and the support circuitry isn't going to be far behind. I looked it up, and it's a long obsolete IC with minimal information. A couple of the Chinese parts companies say they can get them, like UTSource, but they're on their Chinese New Year holiday and nobody is going to be available until February.

If this were some proprietary form factor PSU, it'd be worth repairing, but it's just a generic ATX power supply with a custom wiring harness. I'd recommend just getting another PSU and wiring up an adapter, or graft the wiring harness from the dead PSU onto a working one. It's a lot of work, but it's a more guaranteed fix.

 

[Bentendo64]

Good catch on the crack.

I will move down the path of ATX conversion. I might try de-pinning the connector rather than swapping harnesses, unless the number of contacts for each voltage is wildly different. It seems most everything is labelled on the PSU board, so it shouldn't be too bad! Also, it looks like most of the colors are standard.

Do ATX PSUs have -12V standard these days, or are they more difficult to find?

EDIT:
I think -12V is standard, but the Apple PSU is rated 0.5A at -12V. Anyone know how important this capacity is?
I might suggest this to him: https://www.newegg.com/msi-mag-a550bn-550-w-80-plus-bronze-certified/p/N82E16817701012, but it is rated 0.3A at -12V.

 

[GiGaBiTe]

The -12v rail is barely used anymore, it should be fine with lesser current.