Good thoughts, thanks. I think the HOT and its driver (TEA2037) are okay: there's a sensible signal at the HOT gate (not itself diagnostic), and a reasonable voltage appears on the one flyback secondary I felt comfortable to test with a 10x probe. When I retrieve my 100x probe from the office I can probe the higher-voltage parts of the horizontal circuit, but it looks like that's not the source of the problem.
I will have to get my hands on an isolation transformer. Any particular reason to put the isolation transformer on the scope rather than the monitor?
I guess I could also just try replacing the TDA4605 and see what happens.
Money woulda' been better spent on Apple stock, whodathunkit?
A 400-500MHz 750CX would be nice to try in my Duo 2300c and the 6290 which has a cache SIMM. It's lowend NuBus architecture, so nobody ever looked at that slot, much less the machine for accelerator development. I wonder which package CPU is in my 5300c? ce version's BGA IIRC. That would be fun to look at, as well as the 3400c.
Are the ZIF processor cards in the BeigeG3 straight up Motorola parts? Looks kinda like that from the docs I've dug up.
Have you tried installing the generic Apple network extensions - I don't think I've come across any ethernet cards that needed a specific driver, all worked out of the box with a software reinstall of Mac OS.
Does anyone happen to have driver software for a SMC NuBus 10/100 Ethernet card? The driver software is called 'EtherPower 10/100' I believe. The controller is a 'FEAST' chip. Any help would be greatly appreciated. Kind regards, Jeroen