@ Plimpington2
"On the other hand, my SR-838 is giving me the red ass!!"
What is the problem with it?
The problem with it is that it "jitters" for lack of a better term. I can get the speed more or less close to 33+1/3, but within a narrow band, my strobe reflection oscillates back and forth. As a result, it sounds drunk. I have been repairing and rehabbing vintage amplifiers and receivers for the past year or so (my last was a complete rebuild on a G9000), but this is my first direct drive quartz locked TT, and it's breaking me.
When I got this thing (about 3 months ago, I think), the speed was way off and strobe would not light at all. I couldn't get it above 24 rpm. I got into it this past week, and determined I had a bad transistor and diode on the PSU board. Replaced those (and the neon lamp for the strobe), and now have decent voltages off the PSU and the strobe works. While I was in there, I did all the capacitors and replaced another diode on the speed control board. I was finally able to set the speed. But there is no speed stability whatsoever. It's a mess.
It is my understanding from reading the service manual (at least a million times) that this thing regulates speed in one of two ways - first, by using the quartz lock system that compares frequency data from a speed sensor monitoring the motor with a reference frequency generated by the quartz crystal (after being divided down a dozen times or so from Mhz to something manageable) - and second, by generating a frequency (I guess) from a CR circuit and comparing that to frequency data from the motor. I'm not entirely sure about the second method. The thing is, I have the exact same behaviors whether I have quartz locked engaged or not engaged. I think it uses one method OR the other depending on whether I have the quartz locked button engaged or not (and the fine speed "pitch control" only works when quartz lock not engaged, correct - I should check the owners manual for that). AND YET, I feel like these two systems interact with each each other even when quartz locked is engaged.
What I am trying to determine from a threshold standpoint is whether I just need to continue adjustment of the trim-pots on board to solve this issue - or does this portend a fault on either the speed control board or the motor control board (or worse, a problem with the motor itself). I have checked all voltages on the speed control board (and a few are off, which is why I am surprised by I was able to set speed), and more ominously the DC voltage on pin 9 of the quartz associated IC (which represents the test point for the oscilloscope if I want to dial in speed that way) is all over the place. It's not steady. I have not checked voltages on the motor control board yet.
I'm going to monkey around with it over the next few days, and if I can't get it sorted out, I'll put up a separate thread here to look for assistance.
