Within a couple of weeks of purchase, the system completely died – black screen. I thought this could have been the analog card or the power supply. When I took the cover off and turned the machine on, I was intrigued to see a beautiful blue corona on the flyback transformer. This is the component that creates the high voltage for the cathode ray tube.
The tracks are at 5 o’clock on the image above. It did cross my mind that, as the fault was visible, it may be fixable from the outside.
All the macs seem to have some high voltage putty around the anode lead. Perhaps this putty had failed, or perhaps a crack had opened up.
There is a lot of fear out there on the internet about disconnecting the lead on the CRT. I used a grounded screwdriver to discharge the CRT (a non-event) and then some long-nosed pliers to allow the high-tension lead to be disconnected.
I bought some high voltage dope (like an insulating varnish) and after carefully cleaning I applied three coats. The cleaning included scratching out the two carbonised, self-sustaining, tracks that had been burnt into the outer shell of the flyback transformer.
It did end up with some bubbles after operation, so perhaps it hadn’t cured for long enough. Nevertheless, it did the job and continues to do so.