...and I just stopped by to say: that person is me. {8^>)
I have therefore stopped in and joined the group to say thank you, Stan, for posting all this, and thanks to all of you; to Tom I say: you were right. I couln't believe I found this slightly arcane information. In the process, I've learned *not to touch* those tunnel diodes.
I have a 475, on which the trigger control has been drifting for a few years, requiring a more greater and greater excursion clockwise to obtain a stable trigger. Not a problem for a while, but the most recent time I fired it up, it seemed so far off the mark that I finally decided to have a good sit-down with the manual to see what might be going on. Of course, I first tried the trigger centering pot, but it, too, wound up in a far-clockwise excursion, to little effect.
I traced the problem down to having 1.4-ish volts on pins 3 and 14 of U520, instead of 0.7v as called out in the manual. The "B" trigger works as expected, is just about identical, and it has 0.7v on those pins. How this had happened, and why, was a bit beyond me. I was unsoldering resistors, thinking they'd drifted and left a transistor's bias all wrong. No dice there.
Well, then I found this thread, and here I am, "someone" seven years "in the future", benefitting from Stan's work.
Thanks again guys. My 475 was military surplus and from a pretty late production run (the manual is dated 1977), purchased from eBay for a great price, and the thing is just nearly pristine. I really lucked out. But then I'd been looking for a really nice 465 or 475 for a good while, having bought a 531 from a really nice fella in 1997 or so for $50.
Yes, the 531 still works, and works quite well.
bc
