Green Screen and Freezing on G3 iMac CRT

Question

Hi - My son's Snow Slot Load 500mxh G3 iMac has recently developed some problems. It happened not long after updating to Tiger but seems not to be related to that. I installed the firmware upgrade before updating and the install went fine. It was working fine for a few weeks but started freezing up at random times requiring the power button to be held to restart. It would then restart and work fine but over the last couple weeks, the freeze ups have become so frequent that it's basically not worth bothering with. The freeze ups seem to have some sort of mechanical aspect to them - there is an actual flash or flicker or surge type thing as if the power was interupted. I have plugged the iMac into different power sources, etc. to be sure that it isn't somehow something in the houses wiring but that has not effect. In addition, in the last week or so, the screen has taken on a pronounced green cast. At first this problem was intermitent but now is pretty much permanent (it did come on once properly) It still works fine in terms of resolution, positioning, etc., no weird artifacts, just green. Both of the problems persist even if the iMac is started in OS9 or from a CD. I ran the Apple Hardware Diag CD and it gave a clean bill of health on everything....hmmm!
My guess is that it is a hardware problem and the obvious choice would be the video board. I don't want to put it out to pasture since it works great for my son but I also don't want to put bunches of time and $$$ into it swapping out different boards to try to figure the problem. Does anyone know any fairly definitive tests to determine if it is the Video board or, if not, what it is?
Thanks in advace for any help.
iMac G3   Mac OS X (10.4.9)   Slot Load CRT 500mzh Snow

Answer 1

both the CRT and at least the High Voltage section of the PAV are likely bad. Right?<</div>
No only the PAV sounds like it's going bad. The fact that the CRT lights up means that it's good. The silver box on the back of the CRT that Apple refers to as the Video Board is part of the PAV. In fact when you replace the PAV you want to keep that same Video Board with the CRT so it involves cutting and splicing of 2 wires.
Let the HV on the PAV die and use an external Monitor<</div>
Most likely it's the flyback transformer on the PAV that is going and when that goes it's usually it's the Anode section that dies.
If I go with one of the options using an external Monitor, do I need to disconnect the internal CRT? I mean, I know that I don't have to disconnect the internal CRT to use an external Monitor but would it be better to?<</div>
Well if the Anode section dies then mute point because the HV will be gone anyway.
Replace the PAV, use an external Monitor<</div>
If you replace the PAV (deadly voltages involved! Also working PAVs are hard to come by) you wouldn't need an external monitor because the internal one would then work. My son has a 700 Snow that I dropped a DVD-ROM from a 500 Graphite into. Had to use Pacifist to get it to work. Hooked up an external LCD. Now he's watching Pirates II in stereo. He also uses it for Garage Band.
R