imac g5 1.6ghz 17" power supply

[Toasty]

Re: imac g5 1.6ghz 17" power supply

No progress. Set aside as I've been swamped with other work.

I have yet to determine why it's shutting down and why the 24vsb is very low at 16-18v. Usually it's not below 20-21v, as Youfo posted, 20.7v. I believe its a related problem, but I can't seem to determine why its pulled down. The TOPSwitch is working, as evidenced by the 5vsb & not nearly 24vsb.

Youfo ordered the FETs. I'm hoping his is resolved with them. I know this one was not.

-YET-

Toast

[youfo]

Re: imac g5 1.6ghz 17" power supply

Youfo ordered the FETs. I'm hoping his is resolved with them. I know this one was not.

Toast

The parts have not arrived yet. I'll post the results after I receive them.

Charlie

[youfo]

Re: imac g5 1.6ghz 17" power supply

Success! Maybe.

The PHD101NQ O3LT'S arrived yesterday, and today I soldered a couple of them into the 12V circuit. Voila! All of the output voltages look good. I left the PS powered up for a few minutes, and nothing popped or smoked, so maybe it's good.

I keep saying "maybe" because I'm troubled by the burning around the 3.3V circuit. I mentioned this in an earlier post, and I think it's the same part of the board that Toast referred to in post #38.

Violating my usual safety concerns, I powered up the PS with the case off, and took some readings with an infrared thermometer. The diode circled in the photo (which was taken before the MOSFET's were replaced) read a temperature of over 220F after the board was on for about 2 minutes. Some of the other components in that area are also warm, but that may be just conduction from the diode. I'm not 100% sure that the diode is the heart of the inferno, but it looks that way. None of the other components on the board were anywhere near this hot.

I have no clue what would cause this diode to be so hot, or what function it performs. I don't want to button up this PS and call it good without knowing more about this potential failure point.

Anybody have any ideas or suggestions?

[Toasty]

Re: imac g5 1.6ghz 17" power supply

I'm going to look at it again. I don't know where/how that diode fits into the picture, but the one next door looks to be in an identical circuit. I just have to see what it does.

What are your 3.3v MOSFETS? The 3 units I have here use ST D100NH03.

Toast

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Edit timeout.


[EDIT: 220°F - 105°C is extremely hot for that diode or anything in that area. Something is seriously wrong. Tracing this circuit out is the only way.]

[youfo]

Re: imac g5 1.6ghz 17" power supply

What are your 3.3v MOSFETS? The 3 units I have here use ST D100NH03.

Toast

The 3.3V MOSFET's are PHD101NQ 03LT, same as the 12V ones. They seemed OK when I tested them before, but I'll check them again.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Keep an eye on those outputs for rising temps under no load. I had the 12v pair go for no apparent reason under -no- load. Supply just shut down and I found one of them had shorted.

[youfo]

Re: imac g5 1.6ghz 17" power supply

I have some of the PHD101NQ 03LT MOSFET's available if anyone is interested. Just send me a PM by clicking on my member name on the left.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

I will take you up on that as soon as I figure out what is causing this diode overheating problem. Installing new ones without doing so is just going to pop them quickly.

Have you run the system with the repaired unit?

Toast

[youfo]

Re: imac g5 1.6ghz 17" power supply

I will take you up on that as soon as I figure out what is causing this diode overheating problem. Installing new ones without doing so is just going to pop them quickly.

Have you run the system with the repaired unit?

Toast

Another member is also interested in getting the parts. I bought 10, used 2, and have 8 left. I was figuring on keeping another pair, and getting rid of 6, but if 2 of you guys want them, I might let all 8 go.

No, I haven't tried this PS in an iMac. This one came out of a friend's machine. I bought another PS, which worked fine after recapping, and gave the computer back to her. So presently I don't have an iMac to test it in. If I could be sure that this one is OK then I'd sell it on ebay, but I won't do that unless the mystery of the hot diode is solved.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

If you can turn-'em-and-burn-'em, please do so. Don't wait for me. It's no sweat.

I'm not putting them in until I have this solved, and as I've said before, it is not a priority. I have several other -regular- units (AcBel) that just need a recap to get going. Nothing as wacky as this one.

Toast

[Jon B]

Re: imac g5 1.6ghz 17" power supply

I replaced the 2 bad FETs and tried to test the supply and no go.

The same FET on the far right just shorted again with no heat, smoke or sound just gone.

Has anyone figured this one out yet?

In the mean time I have recapped 3 more logic boards and supplies with no problems at all.

Thanks to all.

Jon

[Toasty]

Re: imac g5 1.6ghz 17" power supply

The hot diode area is the cause, or at least part of the issue. Could be the PWM chip next to it. I have not touched this since my last post as it became too involved in tracking down the root problem.

Mine also did the same as yours in blowing the FET. The diode area got hot and that was it. It was on a current limited mains supply and it still popped. That gets expensive quickly after the 2nd one.

I am recommending anyone with the Celetronix units that fail to go to another brand (AcBel or Delta). These are over-engineered and overly complicated when it comes to repairs.

[Jon B]

Re: imac g5 1.6ghz 17" power supply

Yes, I have abandoned this type as well. If anyone wants the board for parts just pay postal fees and its yours.

Thank you Toatsy for all of your help.

I hope I can help you out sometime.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

Sending you a PM with address. I will certainly add it to my collection...

@ youfo - Sending a PM as well to acquire your parts.

Toast

[murf64]

Re: imac g5 1.6ghz 17" power supply

After reading these posts, I've managed to get two celetronix psu's running. I want to thank and give all credit to those who figured out this problem, especially youfo and Toasty. I wish I understood how you analyzed this. But here's what I did with your information, I'll start with the second unit I came across.

The second (psu#2) came from a 20" G5 I bought that also needed a the motherboard recapped. After recapping the motherboard I still couldn't get the computer running because of the bad psu. I had another 20" G5 (my wife's) that also had a celetronix psu (psu#1). I opened up psu#1 to try to get an idea of what the voltages should be at different points on the board. After jumping it to get psu#1 on I had good voltages for a while, and then something smoked and all except the standby voltages dropped. Bummer, did I mention this was my wife's computer.

I went on eBay and bought a dead acbel unit (psu#3). I recapped this one and also changed q1 (a p2 transistor from reading other threads on this forum) and that did the trick, so the wife talks to me again.

I set the two celetronix units aside for awhile, but this week I thought I'd take another look. I removed the mosfets circled in post #43 from psu#1. One, I think the outer one, tested bad, the inner one tested good. I then removed the same two off psu#2, and again the outer one was bad. I then took the two good mosfets and put them both back on psu#1. I put psu#1 back in the iMac I had bought, and it worked. It's been running all week. Note: I didn't want to bench test it again because I suspect having no load on it might be what caused it to fail in the first place, and I didn't want to repeat this.

So on to psu#2. I scavenged a couple mosfets, larger ones, off an old computer motherboard and an old dead laptop psu. I bench tested both of these, they were good. They were larger and a tight fit to solder them to psu#2. I also had to replace that diode that runs hot, and a bunch of p2 transistors I had taken off psu#2. I should note that these parts were good, but psu#2 had become my scavenge board until I thought I could repair it. I pulled psu#1 out of the iMac bought, put psu#2 in and it fired right up.

So in summary, for a dead celetronix unit checking that outer mosfet might be a good place to start.

[alexanna]

Re: imac g5 1.6ghz 17" power supply

Identical to the replacement PSU that nwd purchased when we could not figure out the burned coil scenario. Although brand new and functional, he sent it in and I did a full recap anyway. All Panny FM's. It has been operating perfectly since April 2009.

He subsequently incurred the wrath of a lightning strike on his unit. Power strip protector failed. It was sent to me for repair and I found that it took out the MOV and fuse, but the supply was otherwise undamaged.

Toast

This looks to be the same power supply ,and the MOV is open.
After I repair the open MOV, How can I turn this supply on to test on the bench?
It is probably in here somewhere,I just can't find it.

[Toasty]

Re: imac g5 1.6ghz 17" power supply

The same as you would any other PSU.
Connect that wire in Pic #2 to the negative of the PSU output. I typically use a 47Ω resistor. Gives me a safety margin if something is FUBAR'd.

If the MOV is open, then the fuse might have popped, I would think...?

The MOVs are either Blue or Tan.

Or, do you mean the NTC Thermistor which is either Black or Green and shrink wrapped?

In either case, I would test this with the Series light bulb before a full power attempt:
Post #23: https://www.badcaps.net/forum/showthread.php?p=72692

Check 3.3/5/12v outputs -both ways- with an ohmmeter with reference to output ground. I use an analog meter for this. You may need to use the Diode Check function on a DMM.

*If* you get a low reading on any of them, you have blown output FETs. At that point, I recommend replacement of the entire PSU with either an AcBel or Delta unit. PM me please if you need to do this.

See Post #10 for iMac LED indications: https://www.badcaps.net/forum/showthread.php?t=7124

See Post #37 for Connector Pinout: https://www.badcaps.net/forum/showthread.php?p=78821

See Post #12 for Connector Diagram: https://www.badcaps.net/forum/showthread.php?t=7016

Toast