Imac g5 video display issues

[568129]

Hello,

I have a 20" 2.0 ghz Imac g5 rev b with ambient light sensor model number M9845LL/A.
When I start it up it does not boot and I get no video and the fans are roaring loud. The third diagnostic led doesn't light up on the logic board meaning the logic board and the lcd are not communicating. I tried connecting an external display and the external display gets no video from the Imac g5. I have heard of the bad capacitors problem on the logic boards however the capacitors show no sign of visible damage on the logic board, they capacitors aren't leaking or even swollen at all. I have heard of similar imacs that have had gpu problems and these are fixed with reflowing. What do you think the problem is? I really would appreciate the help!.

[Toasty]

Re: Imac g5 video display issues

Confirm PSU is providing all voltages correctly.

Any chime?

Try booting from the CD. Hold down C when starting up and keep holding.

Bad caps will not always show. If these are Nichicon HM's or HN's from before 2005, they're bad or will be going there soon.

Toast

[568129]

Re: Imac g5 video display issues

PSU is giving voltage correctly as diagnostic leds 1 and 2 are on on the logic board.

Yes I hear the apple chime when I start it up.

Tried booting from cd, it doesn't boot from CD. I tried holding down the c key however I still get no video and fans start roaring after a while.

It has rubycon capacitors and they show no visible damage.

The overheating led is not on so its not overheating.

I am leaning towards bad soldering on the gpu. Perhaps a gpu reflow with a hot air gun is worth a try or maybe with some alchohol just like this: http://www.youtube.com/watch?v=DMsjC...eature=related

Do I have to remove the whole logic board to reflow the gpu or can I just remove the heatsink to get to the gpu?

[Toasty]

Re: Imac g5 video display issues

I believe the overheat only applies to the CPU. Not sure though...?

Have to remove the board. The screws for the heatsink come in from the underside.

You can try the heat gun at your own risk. Too much and components come off the board.

There is a company in CA that does the reball (not reflow) for ~$100.

[568129]

Re: Imac g5 video display issues

I tried the gpu reflow to no avail. I heated up the gpu chip on the logic board with a soldering iron with some aluminum foil on the tip of the soldering iron. In the gpu reflow, the only thing you apply heat to is the black ceramic piece on the bigger green chip or do you apply heat to the green part too. I put her back together and now i still have led no 3 off however led 4 is on so its overheating and it turns off after a minute.

[568129]

Re: Imac g5 video display issues

So this time I tried the reflow again however with a hair dryer and heated the gpu for a minute from 4 inches away and then i heated the gpu for 3 minutes from 1 inch away. I placed aluminum foil around it so the capacitors and other stuff doesn't get too hot. I reassembled partially and guess what led 3 came back on and got to see the video. I turned it back on after I reassembled totally and I got a good 3 minutes of video out of it until it went out again with the same problem no video. I guess the reflow worked only for a little while. I will try to heat it up for some more time with the hairdryer and see how that works however I am going to think about getting a heat gun as I guess the hairdryer doesn't get as hot as a heat gun.

[568129]

Re: Imac g5 video display issues

Hello I am writing this from an imac g5! I reflowed the gpu or graphics card/ graphic chip on the logic board for 8 minutes with the hair dryer. So far I have been using this computer from about half an hour ago without a problem. Knock on wood.

[Scenic]

Re: Imac g5 video display issues

Hairdryer? Reflow!? WTF
That's not gonna last..
Get it reballed (post #4) or forget about it.