Imac Isight G5 PSU repair

[doanh]

I am starting a new thread per recommendations of experienced bad caps member.

I have a 20 inch Imac G5 Isight. My PSU is dead and I could use some guidance on how to diagnose the problem. The part number is 614-0378 with the attached images.

The Imac light just blink.. nothing else is happening when I push the "ON" button.

I searched the forum but no luck so far. Help?

[Behemot]

Re: Imac Isight G5 PSU repair

Try typical procedure - first look for shorted diodes, transistors, blown fuses etc.

[Toasty]

Re: Imac Isight G5 PSU repair

You are getting some indicator light, so perhaps the supply is not bad or only working in standby? From the label of others, I see that it is a single voltage supply, 12v. Can you verify the output? What are the markings on the board for the black, gray, and brown wires?

Toast

[doanh]

Re: Imac Isight G5 PSU repair

Thanks.

the computer just blink at the front panel and that is all. I see a 12V label on the gray so it may be safe to assume the black is ground and the brown is 24V?

This board is not easy to diagnose on the top side. Is there a schematic for this board somewhere?

[doanh]

Re: Imac Isight G5 PSU repair

RTN2 for the black and PFW for the brown? no clue to what that could stand for.

[Toasty]

Re: Imac Isight G5 PSU repair

24v?? The supply is labeled for 12v, nothing else.

Measure from Black to Gray and to Brown. What voltages do you see?

Toast

[doanh]

Re: Imac Isight G5 PSU repair

the 24V was just a wild guess for the brown wire.. since the gray wire is 12V.. I will hook it up and check.

[doanh]

Re: Imac Isight G5 PSU repair

black to gray, I am getting 12V on both gray terminals. Black to brown, close to nothing or in the low mV region.

I am also nearing a relatively high pitch hum too.

[Toasty]

Re: Imac Isight G5 PSU repair

I'm guessing but the brown could be either a voltage sense from the mainboard or the on/off control to the PSU.

The squeal could be an indication of bad caps in the unit. Are there any under that copper heatsink enclosure?

Toast

[doanh]

Re: Imac Isight G5 PSU repair

nothing underneath the copper heat sink enclosure.

There is a small (start up?) cap underneath the large 420V cap though..

no signs of bulging on any caps though.

[doanh]

Re: Imac Isight G5 PSU repair

Studied the board a little more and noticed one pin is missing on the IC chip.. attached image. This chip looks heat stressed compare to the bottom chip. chip labeled LM339G PCT610?

[Toasty]

Re: Imac Isight G5 PSU repair

>>no signs of bulging on any caps though.<<

Just means the caps haven't bulged. Says nothing as to their condition.

>>one pin is missing on the IC chip<<

Looks like a factory modification. Chip is probably fine.
Can not see chip condition due to out of focus pic.

Recommended that you replace all caps except the large mains cap.

Please supply for all caps:
Diameter & length in mm. - 10x20
Capacitance & voltage - 2200@16
Brand & Series - Ltec LZG

Probably looking at <$15.00 in total.

Toast

[doanh]

Re: Imac Isight G5 PSU repair

Thanks for the help. Sorry for the bad image.

I have (3) 2200 uf at 26V, (1) 1000 uf at 16V, (1) 68 uf at 25V for capacitors..

There are two blue components underneath the copper heat sink but it does not look like capacitors to me. attached image.

Question.. Panasonic has the high temp caps with low impedance. Is this better than low ESR caps?

[Toasty]

Re: Imac Isight G5 PSU repair

Sizes, Series, brand.....?

26 volts ????

[doanh]

Re: Imac Isight G5 PSU repair

sorry, typo 16V not 26V... thanks.

2200 uf at 16V is 12.5x25mm; 1000 uf at 16V is 10x20mm; 68 uf at 25V is 5x11mm.
all are panasonic series at mouser...

any comments on the high temp vs. low ESR panasonic cap series?

[Toasty]

Re: Imac Isight G5 PSU repair

Impedance ~= ESR for all intents and purposes.

Go with the Panasonics.

Toast

[smason]

Re: Imac Isight G5 PSU repair

You're lucky, it's an ACBEL, shouldn't be too bad.
I have a Celetronix from an iSight that I haven't had sufficient motivation to work on yet.

I doubt the missing pin was caused by a problem, if it was there would probably be more damage to the chip. Might be built that way.

My other iMac was just caps. I don't recall the brand of power supply at the moment.
I used Panasonic FM and maybe FC.
Definitely do a full recap and see, you might get lucky.

[freddyfena]

Re: Imac Isight G5 PSU repair

Hi
doanh, are you absolutely sure that only the PSU is bad? Because the mobo usually has whole bunch of bulged caps, I'm actually trying to repair a 17" model now and I have not less than 15 bulged/blown caps. I just got the Imac from a friend and I know it doesn't start and that this is a common issue, read more here: http://jimwarholic.com/2008/07/how-t...le-imac-g5.php

Regards

[smason]

Re: Imac Isight G5 PSU repair

Found the following in several places via Google, can't say for sure how accurate:

No pin numbers known, but these are the voltages:
Grey: +12V
Grey: +12V
Black: ground
Black: ground
Brown: PFW (battery powered signal between +3 and +6.5 volt to switch power supply on)

[doanh]

Re: Imac Isight G5 PSU repair

thanks a bunch! this is very helpful.

BTW.. the MB I am looking at uses surface mount caps and they all look ok to me.

I need to buy a ESR meter..