[DanThe]

The last few days on startup/waking from sleep the screen becomes full of vertical lines/blocks and 90% of the time the machine freezes at the same time, if it doesnt freeze it will do as soon as I click an icon.
I have to turn it off by the power button then restart, it usually starts after a few attempts

Ive seen the problems relating to the later imacs but this is the white polycarb enclosure type and I cant find any info,

Any ideas as to what could be causing the problem and how I check/fix?

Thanks

[seanc]

Failing capacitors in the power supply or on the logic board, or possibly the GPU.

If you're handy with a soldering iron, you might be able to fix it.

[DanThe]

I did have a feeling it was power related, problem happens more often when the machine is cold or has been left asleep for a long period.
The fan had been running a lot more often than normal a few weeks before but that problem was fixed using the disc utility

Here is a pic of the screen for what its worth

[seanc]

I don't understand how you could fix heat by running disk utility...

Open the back up - lie it face down, unscrew the 3 or so screws on the speaker/vent panel and lift the back panel up. Take a good clear picture of what you can see. Look for any bulging capacitors - cylindrical towers, should be flat, not bulging, wonky or with orange crusty stuff.

[DanThe]

I know what your saying but it stopped the fan running as much, as soon as it repaired the permissions.

No signs of overheating at all inside, all capacitors are like so



So I removed the power supply and opened it up, same story, everything looks fine







I removed any other covers that looked like they were hiding capacitors and couldn't find any obvious signs

[Big Mac]

Originally Posted by DanThe 

I know what your saying but it stopped the fan running as much, as soon as it repaired the permissions.

Okay, but for the record, repairing permissions by itself couldn't possibly have anything to do with fan speed or temperature.

[seanc]

Looks like you have plain old GPU failure then I'm afraid.

Capacitors don't always bulge when they fail, but in cases of the iMac they usually do.

[DanThe]

Is there any fix apart from new board?

[seanc]

You could try reflowing the graphics chip, but you'd need the skills and equipment necessary to do that.

[DanThe]

You mean re-solder the joints? I assume the whole board has to be removed, not my cup of tea TBH

[seanc]

I doubt there are any joints for the graphics chip that you can access, it's most likely a BGA mounted chip. You'd need to heat the chip from the top and hope that the joints underneath will reflow.

Could also be bad video memory.

[DanThe]

Are there any applications I can use to pinpoint the problem? Somebody mentioned a 'hardware checker'

[Big Mac]

There's a Hardware Test that is one on of the system discs that came with your Mac. It's clearly a GPU issue, but I don't know if you can narrow it down much more than that.

[DanThe]

Well the problem still occurs on start up, ive been using the machine everyday, every so often it will start up and be fine, but mostly takes several attempts of switching on/off by the power button to start up, once started it will stay on all day without problems but only because I have turned off the sleep function
Im guessing this is most likely to be a joint problem as its not got worse? So it would be worth a shot at having the joints re-flowed, sound reasonable?

[seanc]

http://i11.photobucket.com/albums/a1...rborow/ps1.jpg

Top left, United Chemicon cap looks like it may have a bulge.

[DanThe]

So it might not be a GPU problem after all?

[seanc]

You'd need to confirm if it is bulging.

If it is it just means it's obvious, the rest could be bad as well, they don't always bulge when they fail.

[DanThe]

Just had another look, they still look fine





Will see if I can borrow a different power supply to try out

[DanThe]

Another update, the USB ports are now dropping out randomly, I have a bluetooth dongle that I normally use in the side of the keyboard, it rarely works now.
The printer is also hit and miss, most times it will have a bit of a twitch like its about to start printing and then the notifier pops up and states 'communication error' I can then only print after a restart

The keyboard and mouse both plugged into the back of the machine still work fine though, never had a problem with these.

I didnt manage to get a power supply to try out, but I did get another spares/repairs imac (same as im using) with bulging/leaking caps on the motherboard. Tried it out and it worked fine for an hour or two then died and refused to start up, even after being left overnight to cool down.
I may buy a kit to replace the caps on the board for this machine, but I should be getting a later 22 inch imac in the next month or two so will see how long I can put up with it for

[seanc]

Did the spares/repairs iMac not come with a power supply?
Have you checked it out?

[DanThe]

No it didnt unfortunately, otherwise I would have tried it

[seanc]

Well my vote goes to re-capping the spare board and seeing what happens from there.

[DanThe]

Just put the spares/repairs machine together with my HDD, memory, power supply and the 25 new caps, funnily the new caps that came are the same as the caps fitted to my original imac, which says to me the problem might not be the caps on the board The caps that came out were well gone, the legs came off 2 or 3 pretty easily.
Will have to see how it goes, any more grief and the power supply will be getting some new components even though the caps in there still look perfectly fine

[seanc]

Now hang on there a moment.

The replacement capacitors are most likely the same manufacturer and a similar series, only they're not in the date range when the bad caps were manufactured (hopefully!).
Open up my Dell SX280 and you'll find *new* 2009 dated Nichions all over it (replacing the failed 2004/2005 old ones), it was much easier to get Nichions in the correct sizes and specifications than Panasonic or Rubycon caps.

I reckon it'll be fine

[DanThe]

Just had a look at the original board and there is no dates visible on the Rubycon caps, Nichion is what came out of the spares/repairs board.
Restarted it 4 or 5 times, put it to sleep several times and let the display go to sleep etc, no problem so far!

Next job = replace the caps on the original board and see what happens

[seanc]

What model/revision number is the power supply?
Looks very similar to mine, with the mains capacitor installed on its side instead.