AcBel 9841 problems

[Toasty]

Re: AcBel 9841 problems

Okay. I have no info on this PSU, so that was an assumption on my part.

There is no hissing:
1) before it is turned on (and 28v is present)
2) when it shuts off and the 28v is still live

Correct?

If so, then I believe you are looking at the outputs as the problem.

Or that NTE or Lelon.

.

[golemmaster]

Re: AcBel 9841 problems

Correct: 28vsb present, switch on hiss and shut off, 28vsb still present uninterrupted by the switch or hiss.

I've replaced those caps twice with other brands despite ESR looking ok on the NTEs. The TEAPOs measure 0.00 - 0.01 ESR and correct capacitance with the ESR-micro 3.1.
Would something wrong with the powergood/poweron section cause this and how to track that down?

I'm confused and getting tired but I don't want to give up because you can't buy this PS without it costing an arm and a leg or without the uncertainty of the replacement failing in a short period too. Also, it would be very cool and satisfying to fix it.

BTW, THANKS for helping!

[Andy3665]

Re: AcBel 9841 problems

Hi,

There are effectively 2 PSUs in one with this power supply. The Gigabit G4's used a 28V start up because of them running an ADC monitor directly from the graphics card. The two small daughter boards on the primary side each have their own PWM on them. The larger board is for the 28V supply. The noise and shut down is caused by the SMD caps going out of tolerance in the RC circuit of the PWM making is ocsillate at too high a frequency. I've repaired hundreds of these over the years, but not much call any more. Are you in UK, I could send you a couple of daughter boards which should cure the problem.

Andy

[golemmaster]

Re: AcBel 9841 problems

Hi!
... the surface mount caps, you say.... Hmmm...
I replaced the small electrolytic caps but hadn't considered the little ceramic SMDs going out of spec.
Any idea what their values are supposed to be?

THANKS!

[jantoman]

Re: AcBel 9841 problems

Just finished to fix a faulty AcBel 9841 PSU... I followed the suggestions on the first post replacing the small caps on the daughter boards, along with some others on the main board. One of the fastest fix I ever done: I reconnected the PSU to the main board and got the Apple chime at once. I LOVE this forum. Thank you so much