Imac G5 - lines on screen

[dodle]

I've inherited an Imac G5 from a friend who was having problems with it. I am hopeful that I will be able to get some hardware support.

The problem is that when the computer starts up, the screen is covered in distorted lines... like the pixels are all messed up. I can see the machine starting up, but nothing is legible. Is anyone familiar with this issue, and is there a resolution?

[stream303]

The first thing you should do is check to see if the serial number falls into those ranges of G5 iMacs that had have problems with both video and power issues:

http://www.apple.com/au/support/imac/repairextensionprogram/

The main problem is that support for this fix seems to have been cancelled:

http://www.apple.com/support/imac/repairextensionprogram/

You may want to immediately check if the unit is full of dust by loosening 3 screws on the bottom (center, and furthest outward screws - they don't come out) and with the power disconnected, pull the back off.

If you want to blow any dust out, be gentle! Don't spin the fans too hard as you can knock them out of alignment.

Most importantly, especially if your system serial numbers fall within the ranges shown above, check the health of the capacitors - the small cylindrical components that have a shiny aluminum top. They are usually etched with an "X" or "K" pressure-relief.

None of these should be leaking any gunk, and the tops should be flat - if the tops are convex, or bulging, the caps may be close to failure.

Check to see if the power supply is getting too hot. With the unit assembled, run the back of your hand across the outside lower front bezel where the apple logo is. It should be uniformly warm, and not have any definite hot-spots.

[dodle]

Sorry I hadn't replied sooner. I had given up on the IMac for a while. It turned out that the problem was capacitors. The ends were bulging with gunk that had leaked out.

Removing the capacitors wasn't as easy as I thought it would be. Just a couple of days ago I replaced some in a power supply (which didn't fix the problem). It was a snap, just heat up the solder and they pop out. In the IMac, I had trouble melting the solder. So I just broke the faulty capacitors off and took them in to get replacements. When I returned home I attempted to heat the solder again to pull out wires torn from the capacitors. But it would not get hot enough to melt. I'm guessing that Apple uses something other than average solder, that takes a much higher level of heat to melt. So the only thing left that I could think to do was drill (which probably isn't normally recommended).

I had to buy a new electric drill and the smallest bit I could find, 1/32". I very carefully drilled over the old holes, where the wires were stuck in the board. The new holes turned out to be a smidgen bigger than the old ones, but fortunately the board wasn't damaged. I soldered in the new capacitors (which were a little bigger than the old ones, so I had to bend them over to get the case back on) and fired up the machine. It appears to be working pretty well, but needs a hard drive. So I'll have to pick one up if I want to actually use the thing.

If I leave the machine running without booting into an OS or a disk, the lines will reappear sometimes, but not nearly as bad. I believe this means that there are still faulty capacitors in the board and I will have to replace them all at some point.

Thanks stream303, that was very helpful.
*dodle presses stream303's "thank" button*