Re: Another sick iMac G5 PSU

Toasty,

I'll try to revise the connections and draw everything from the beginning.

I did not test all of the transistors, because I thought that section of the circuit was dedicated only to the other voltages (+5V, +12V and +3.3V). But if you really believe I should do that, then I will.

The markings in R70 were unreadable, even with strong lenses. I took that value from the datasheet. I thought it could be correct, once the caps surrounding it had the same values on the board and on the sample circuit of...

Re: Another sick iMac G5 PSU

Wizard,

I've made a mistake when uploading the schematic and it was cut on the right side. Now I'm sending it complete. I've also drawn a thin blue line separating hot and cold side. Hot side is left, cold is right.

Last night, after my previous post, I could not sleep and decided to try to change the MCR100-6 that I had bought. No change. I finally decided to replace also TOP247 with another one. No change.

The PSU still makes a noise (something like a very brief "cheep!", with nearly 3 seconds...

Re: Another sick iMac G5 PSU

Toasty,

Thank you so much for your help. It is specially very useful to know who was the maker of the board.

You are right. R70 is placed between C39 termminals and is connected to it. C41 is a SMD cap. I'm attaching a little schemmatic (very basic and quite incomplete) for this section of the PSU. I hope it serves to make easier for me to explain what I'm doing. Maybe it's also useful for someone else.

Correct me if I'm wrong, but it seems to me this section is independente of the others and it should work...

Re: Another sick iMac G5 PSU

Well, new developments.

I've replaced the optocoupler and turned the PSU on. The tensions are still wrong and now the PSU makes a ticking noise. It ticks something like once a second. Another problem is that now TOP247 gets hot. I haven't measured the temperature, but it is still possible to touch it and keep the finger on it.

Checking other components close to the TOP247, I found resistor R70 open and the capacitor close to it (C41) seems to have some leaking. I've removed the resistor and confirmed it is open, but I didn't...

Re: Another sick iMac G5 PSU

I've got some news.

Measuring the voltages on TOP247, I found out that the tension on the pin connected to the optocoupler SFH615 was always the same (5V), no matter what the PSU output was (yes, it was changing each time I conneted it to mains).

I decided to take it off the board and test it. Not to my surprise, the photo-tansistor side of the optocoupler was shorted, keeping 5V at one of TOP247 pins (I believe it's the regulation one).

I'll try to replace it tonight and see what happens.

...

Re: Another sick iMac G5 PSU

Toasty,

I've taken some pictures of the PSU. Sorry they are not very good, once I've used a cell phone for that.

I hope the problem is the diode. I wouldn't know how to replace a transformer like that.

I had no time to replace the diode last night but I'll try to do that tonight. Do you believe I could use UF4007?

Seanc, thanks so much for the info. I'll try a little more with the 247 and if it doesn't work, I'll go for the guy you pointed.

Best regards,

Emer...

Re: Another sick iMac G5 PSU

Hi, Toasty!

Thanks for the answer.

The Apple part number is 661-3627. Mains voltage is 220V.

I'm not at home right now, but when I'm back there latter, I'll take some pictures to post here.

Is the flyback diode the one that is connected parallel to the transformer primary? If that's the case, I've tried to test it and it appeared open to me. But, reading another thread in this forum I saw a post from you saying that it could not be measured with a ohmmeter, and that it would test allways...

Hi, everybody!

This is my first post in this forum, so I'd like to start saluting all of you guys who provide this great help to us who suffer from the capacitor plague.

I happen to have a iMac G5 17" ALS that was dead when I bought it. I had to replace the mobo, once the recapping was not enough to bring it back to life.

It's PSU was also damaged, but I managed to make it work by changing the caps and one of the transistors close to the PWM IC (3845).

Some weeks ago, a power surge killed the PSU again. When I tested it I could...