Apple iMac G5 PSU - Recapped, now not working again

[Player2]

I am working on a 20" G5 iMac which was having power supply issues. This is the first gen G5, no iSight and no ambient light sensor. Model number of the PSU is 614-0353 Rev B.

I received this machine with a power supply full of blown caps. Replaced them all with appropriate, reputable brand caps. It worked great, I left it running overnight to make sure everything was ok. Since then it has been sitting off for a few days, today I powered it up to download updates. It downloaded the first set, then said it required a restart. It shut down and would not come back up. Now I've only got the first diagnostic LED on the motherboard lit, and when I plug the power cord into the power supply I hear a pop. Pressing the power button on the iMac returns no results, doesn't even try to power on.

All the caps on the motherboard are good. PSU caps are still good, fuse is good. I saw some other posts regarding torroids burning up, both of them appear to be ok. Is there some way to check aside from visually looking for evidence of burning? What else should I be checking for?

Thanks!

[PCBONEZ]

Re: Apple iMac G5 PSU - Recapped, now not working again

Check PCB where you did the soldering for burn marks, solder hairs, a splat of solder, or anything that might have shorted.

[Toasty]

Re: Apple iMac G5 PSU - Recapped, now not working again

Disconnect PSU from midplane(mobo). Can you jumper the PSU on?

If yes, then unplug & un-jumper it and wait a few minutes. Make sure the voltages have dropped to zero then plug it in to mobo. Try again.

If no, do you have another you can swap to test system?

Has the mobo been recapped?

Swap power cords. It happens.

[Toasty]

Re: Apple iMac G5 PSU - Recapped, now not working again

Is this the mobo where you had reversed the cap...?

[Topcat]

Re: Apple iMac G5 PSU - Recapped, now not working again

is the PSU an acbel build or a delta? some of the earlier acbel PSU's were prone to other problems beyond bad caps. In most cases, you're just better off replacing it.

[Toasty]

Re: Apple iMac G5 PSU - Recapped, now not working again

Can you provide any specifics on the failures on the AcBel ones?

I've not seen a Delta in these. Only AcBel and the last was a new Celetronix (aka: Red Rocket), which was a preemptive recap.

[Topcat]

Re: Apple iMac G5 PSU - Recapped, now not working again

Can you provide any specifics on the failures on the AcBel ones?

I've not seen a Delta in these. Only AcBel and the last was a new Celetronix (aka: Red Rocket), which was a preemptive recap.

I wish I could. I was given this information from a place I recap a lot of G5 boards for, we were talking one day, and got on the subject of PSU's....and he told me this. I was told the acbel's were junk and the newer G5 Imacs had delta built PSU's in them, which were more stable/less failure-prone. Not being a mac guy, I can't speak anymore intelligently on this, but I'll see if I can get more info, he sends me boards constantly, I usually get 3 or 4 a week from them. He said the acbel failures (besides caps) were +12v outputs.

[Player2]

Re: Apple iMac G5 PSU - Recapped, now not working again

I did install another power supply last night and so far it is running fine. Of course the original one worked for a while too. I am going to go over all of the solder joints now.

The logic board was recapped, but not by me. Yeah, I learned my lesson with that one I reversed. That was a board with the ambient light sensor though, that has the five caps in the lower corner. Replacing the 8mm 1500 uF caps with 10mm made it difficult to see the '+' marks.

The PSU is indeed an AcBel. I was hoping that the fact that it is revision B would be a good thing.

[Toasty]

Re: Apple iMac G5 PSU - Recapped, now not working again

@ TC - Thanks! Any info would help. If he has any busted ones, I'd be happy to take them off his hands.

@Player2 - I do not have any of this model. Would you take some pics when you have it apart? Did you jumper it on?

Toast

[Player2]

Re: Apple iMac G5 PSU - Recapped, now not working again

Sorry for the long delay - I've been sidetracked this week with some unplanned car projects (read: repairs )

Toasty, I did take some nice, large pictures for you. I'm attaching them to this post. I did jumper the PSU on, then unplugged it and checked with a meter to make sure all of the lines were at 0. When I plugged it back into the iMac it still does the same thing. Also, the replacement I put in has also stopped working. The part number on the replacement is 614-0296 rev A, all of the amperage ratings are identical.

Out of desperation, I decided to recap the motherboard. It looked like the last person did a pretty clean job, but for peace of mind I went ahead and replaced all with new MCZs. Still won't come on.

By using the power button on the motherboard, I've been able to observe what's happening more closely. The first LED is lit, indicating standby voltage is present. When I press the power button, the second LED lights for less than a second, and it sounds like something is discharging or shorting. Same symptoms with either PSU.

I have been back over the board twice making sure there is no sloppy work that could be causing this. I've also been back over the PSU and touched up a couple spots that weren't perfect. I'm not sure now though if this is a PSU problem or a logic board problem.

I'm stumped. Any ideas?

[Player2]

Re: Apple iMac G5 PSU - Recapped, now not working again

Okay, I feel like a tard. After trying FOUR (I shit you not) PSUs all with the same result, I decided it must be the mobo and started digging through old threads. I came across one that recommended loosening the screws to make sure the mobo isn't shorting out on the tray. When I read that it reminded me that there was a piece of plastic on the back of the board that was covering the leads for the two caps next to the LCD cable. I peeled it off to solder in the new caps and didn't replace it.

After loosening all the screws, sure 'nuff it powered up! I'm going to put a piece of electrical tape where that plastic was tomorrow, and let it run for a couple days to be sure, but I'm cautiously optimistic.

In my defense, I've recapped several 17" G5s now, none of which have this insulating piece of plastic on the back of the board. This is the first 20 incher I've gotten, so chalk another one up to a learning experience I suppose.

Thanks for the input everyone! Toasty, if you would like pictures of any other G5 PSUs I have a whole slew of them laying around. If you're interested I'll work up a list of part numbers of all the ones I've got now.

[PCBONEZ]

Re: Apple iMac G5 PSU - Recapped, now not working again

If you post them then eventually someone needing them will find it.
-
Make sure you write the model numbers in the text block of the post.
That makes them google searchable for those poor souls that dunno about BCN.
.

[Toasty]

Re: Apple iMac G5 PSU - Recapped, now not working again

At least you know the over current protection is working!

Glad you found the problem Sometimes the damndest things....

Thank you for the pics! Yours matches the 661-3350 (AcBel) model I have. Now I know those two numbers are a match.

TC asked this question several posts back - Is the unit an AcBel or Delta?

Use something more substantive than electrical tape to cover that area. i.i.- A piece of a plastic container cut to fit.

I have had my response in partial form since your 5PM report. Did part, went away. Came back later did a bit more. Saw the pics and grabbed the matching unit from out of its "In Process" tray with a pile of notes and parts to go with it.

It was good I didn't see your later report earlier. Otherwise, I 'd of stopped working on my Imac PSU testing wiring harness and load center. Just tested it on a 661-3350 and it is now just so easy to hook leads to terminal blocks. From which I can now easily connect to the loads I want. A TON of alligator tipped jumper wires just went on furlough. Somebody mentioned Aruba...

I'll take all the pics you can chuck at me. Each post should have this info:
{ Taking my 661-3350 as an example }
Maker: AcBel
Their model #: API3PC96
Apple PN: 661-3350
Rev: B
Date: B0649

===> If I nod off here, just gimme a li'l poke, okay?.....
I'm not as think as you drunk I am....

I was going to have you fire it up with no connection and test for all the juice. From what you said, it sounded like the back-light assembly had "issues". That's what the 24v supplies to the inverter for the back-light tubes.

Then you posted saying you figured out the quantum error between the bench input control system and the benched device.

Let me know if anything else comes up.

Hope this REALLY is solved!

Toast

[Player2]

Re: Apple iMac G5 PSU - Recapped, now not working again

Both PSUs that I mentioned are made by AcBel (614-0353 and 614-0296)

So far the machine's been chugging along without a hiccup for about 24 hours. I found the piece of plastic that I peeled off the board, I will put it back on to replace the electrical tape. The more I am thinking about it, I'm not sure if that plastic is to keep the board from shorting, or to protect the cables that ran under that part of the board (SATA data and power to HDD). When I applied the electrical tape, I also re-ran the cables on top of the board, so it's possible that the leads on the bottom of the board were digging into one of those cables.

I will start a new thread in the power supply section for iMac PSU pictorials, so errant searchers won't have to read through 14 posts of my dumbass mistake to get to them. Then anyone can contribute to the thread. Sort of a holy grail of crappy, Lltec-filled, power supplies if you will.