AcBel 344W SMPSU repair clues and suggestions

[itwentboom]

I'm trying to fix an AcBel AP10PC24 - power supply, 344W from a Mac G4 circa 2002 (has PFC). Basically on power up the thing does the "chirp-chirp" thing as we know, it is trying to startup but its control circuit knows there is a problem. A resistor smokes which looks to be the current monitor for the main MOSFET. I have removed the PSU from the Mac and use a dummy load.

So far, I have tested all the power semis (removal), watty resistors, the caps look OK, so now I'm down to the control chips, ML4800CP (does the PFC and PWM) and a Weltrend WT7515 power monitor chip. There are a few LM339, as we know for comparator duties, do these go faulty?

All I can do is replace these chips but are they likely to be the culprits? The WT7515 comes in 3 types, the markings on the chips are not sufficint to identify the chip precisely for replacement, plus the chip is not readily available.

My first guess is there is a short in the output (LV rails), but all the semis test OK. Clues anyone?

[itwentboom]

Re: AcBel 344W SMPSU repair clues and suggestions

I just remembered, which might be a clue. The PSU goes into "chirp mode" from the instant on plugging into the mains (240V). The "Power On" signal to the PSU is open circuit (floating) as I have the unit on the bench.

[tom66]

Re: AcBel 344W SMPSU repair clues and suggestions

Check and/or replace the startup cap.

[chipmunk]

Re: AcBel 344W SMPSU repair clues and suggestions

Which cap it the startup cap?

[Per Hansson]

Re: AcBel 344W SMPSU repair clues and suggestions

If unsure just replace all small caps.
Photos would help...

[stj]

Re: AcBel 344W SMPSU repair clues and suggestions

just for clarity,
this is NOT an ATX psu.
it could be, but the wires are in differnt places in the connector.

thanks apple - for using the same connectors - you fucking bastards.
i wonder how many pc's you may have killed with that stunt!!
just because DELL did it does not mean you had to!