iMac G5 AcBel 17" API3PC94-290 no voltages

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

Find the short on D23's circuit. (What it supplies)

Probes - seller(s) on eBay have Tektronix pairs for <$15. Not recommending anyone here as I have no hands on regarding if they are legit (doubt it). HP-Tektronix probes are typically $40-$50 each. On Mouser they're near $60. (Pomona brand)

For what you're doing, the eBay ones are probably okay.

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

It appears to supply power to M6. There is a short on M6 (two outside legs) so I think that will need to be replaced. However, when I checked for shorts on another identical bad power supply with the same issues, I did not find a short on M6. I did not remove the D20 and D23 diodes, but I'm not sure if that would make a difference.

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

Common fail on M6 the 24 volt reg. Caps fail and spikes take it out.

Other supply may have one that is not totally failed. Have had them only do 18v as partially failed but not shorted. Replace it and see.

Merry Christmas!

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

parts on order now from mouser I will get back to you in several days. Thanks again for all your help. Belated Merry Christmas.

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

I've got M6 replaced so I'm getting a little voltage now. About 4v at pin 22 on the ouput and about .6v on the ouputs of pins 15 and 8 (un-jumpered). When I put the unit back in the case I don't believe I fully discharged the the main caps and something may have shorted, so I'm getting a chirping sound now about every second or so. It's hard to isolate but I believe it's coming from one of the transformers. Any ideas?

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

What is pin 22 ? What are 15 & 8? Use their references please. Having to dig out the pinout sheet to decode is not fun.

What about 5vsb? Is that back? If 24vsb is down, then there's a short on its output somewhere. What is the input voltage to the regulator of you lift the output?

Which one of the transformers chirping and when? Standby? Jumpered on?

Chirping is usually a shorted output or a bad cap as the unit tries to cycle-on. Caps in correctly?

Toast

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

pin 22 is supposed to be ~24v and pins 15 and 8 are supposed to be 5v. (see my last post for acutal voltages). I double checked all the caps and they are in there correctly. The chirping happens when unit is on standby and immediatly after it is plugged in. Chriping sounds like it is coming from T2, the input voltages on M6 are jumping around quite a bit so when I get about .7v DC on the outer legs and between .6 and 4v DC on the inner legs.

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

The jumping around voltages on the 24v regulator M6 are from the "chirping" attempt to start of the TOP. Something is still wrong in that standby section. Check the output of the 24vsb for shorts. Could be the cause of its blowing in the first place. Check the 5vsb side for overload or bad solder joints.

Do you have a variable bench power supply?

Toast

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

I do have an old AC variac, let me know what I should do or set it at in this case?

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

No. Bench supply means a DC supply with voltage adjust and current limiting.

I like 0-50v units with a 2A or better rating.

Similar to this: http://www.ebay.com/itm/310366977603

Toast

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

I have a short on a resistor at R8 where the AC plug is supposed to sit sort of near M1. As far as the DC power supply we have a million of those at the university I'll see if I can pick up an old one although the one you picked out isn't a bad price. How does one of these help isolate problems?

I replaced R8 so now no voltage goes to any of the pins. My guess is some other components were taken out with it. It also takes an increadibly long time for the main caps to drain as well, which was my initial problem when I put it back in the case and thus caused it to short.

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

>>How does one of these help isolate problems?<<

Allows you to apply a voltage where you have a problem to trick the supply into thinking it's okay. Helps to track down shorts and overloads, hence the current limiting function. Also keeps you from frying a device that has a short on its output, like a regulator.

R8 is a 10Ω, 1/2 watt, fusible resistor. It is in between the positive (+) of C41 mains cap / bridge rectifier positive (+) and one leg of the standby transformer.

Toast

Toast

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

On C28 right next to R8 I checked that disc capacitor with my ESR meter and reads a 10 (ohms I beleive) on a good power supply but on this broken one I dont' get a reading. Is this valid? I usually test the electrolytic caps with the ESR. I get a reading of about 340v on C28 in the good unit and nothing on the bad unit. Another reading that puzzled me was that there was no reading on R8 with the good unit however I do get a voltage reading on the bad unit at R8 of about 340v.

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

When you get 10Ω, you're reading the resistor. When you don't, it's open.

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

I did some swapping between power supplies and D10 is bad also near R8 the code reads T2D, know this is a fast rectifier but it gives me several options on mouser so it's hard to make a decision on which is the right one. Also is it possible that D20 and D23 were taken out? By the way the disk cap on c28 is good (did some more swapping)

wouold this work for the D10

http://www.mouser.com/ProductDetail/...3kaqqrjA%3d%3d

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

re-hash of this device again...

D10 is -not- bad. It's a TVS or Avalanche diode. Finally got this one pegged.

See: https://www.badcaps.net/forum/showthread.php?t=18237

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

I only mention the D10 being bad because when I swapped it to another good power supply I got the chriping again so that lead me to beleive that it was bad.

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

Ok I think I found out why and where there was a short to the power supply. In the attached picture the second leg on the main cap from the right and the ground wire from the AC plug touched and caused the failure. Let me know if this further helps to diagnose the problem.

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

Fixed it!!!!! When I swapped out the c28 and D10 and since you said the d10 isn't bad my guess was that it's the C28 which reads as a 10.3 nF disk cap. On some of the pins that should read 12.1 I get 12.2 I assume this would be within spec.

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 no voltages

. . . post 35:

>>By the way the disk cap on c28 is good (did some more swapping)<<