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As for the big money part of synth repairs, well, it's a nice theory.
He, he. I know the reality.
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I don't really like these numbers, 2nA seems insignificant
OK, I found my mistake, just over-simplification.
Corected, it says the unloaded raw supply voltage must rise above about 14V to bring Q5 on and get power to the regulation servo. We would expect over 14V for a nominal 10V out, but older gear in faraway lands, this has to be checked. (My Leader 'scope, as it ages, has trouble making enough raw DC to be stable.)
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make their descriptions as clearly
You would enjoy both books by T. K. Hemingway. His topics are not synths, but basic and related enough you will gain something. abe.com probaby has a few copies at prices a synth-fixer can swallow.
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great if it starts---which it won't
Hemingway has a few pages on fallacies including this one.
Hemingway on Non-Starters, 1.5MB PDF file
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the best redesign strategy could be to make the threshold of cutout of the starter circuit less dependent on Vbe and beta.
Yes, but how to do that without adding more parts and new bugs?
I eventually realized that we can't leave the R5 R14 path because it leaks turn-on current to Q5 base which R27 might not be able to divert even if Q9 is full-off. Then light-loaded output soars. True, it has substantial bleeder, but still I mistrust a reg that floats high on light load.
The R5 R14 junction must be pulled down fairly far. This conflicts the idea of standing Q2 up on a stable voltage (Zener) for stable action-point.
We can add another and another transistor to get the sensing, reference, and clamping all on different parts. Aside from practical cramming difficulty, many transisors together hanging on a slow analog loop wants to find some quasi-stable point.
There may be a modern Low Battery IC which could be twisted to this function, but that could be hours skimming datasheets and working out the trick, only to find that the part is not really available.
And all on the not-big money Steve can collect from his customers.
While I can't make my cocktail-napkin or my simulator show trouble near nominal 10V, I was a bit surprised how hard it was to to get a soft or hard answer worth trusting. And working out the several temperature effects, and the device variation effects, requires an impractical number of cocktail napkins.