Craig: Thank you!
I should have noted the work done … everything in green boxes in my graphic (aka, every component in the circuit) has been replaced and/or tested OK.
I see the same behavior either with the original 9.1V zener or with a new replacement 9.1V zener (specifically, a NZX9V1D).
The issue (I think) is that for some reason there’s no current through R150 & R151 to create the voltage drop needed at TR17’s base, which once activated would flow current through R146 to activate ZD148.
Despite weeks of scratching my head and trying different things, I can’t determine why that’s the case …
One idea was that the 15V PS load is too small – I confirmed in LTSpice that if the load is 1ohm, the PS won’t engage.
But, I measured the resistance from the +15V PS to ground and am seeing 285ohms. Modeling that effective startup resistance in LTSpice, the power supply should still activate.
(I’d post the LTSpice images, but I’m new to the forum and it won’t let me either copy / paste images, upload them in the image upload tool, or attach them as files for some reason? Is the image tool operational on this forum?)
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