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Hi Ed,
Thanks to your tips, it looks like I've found the video heads to be okay. I recorded color bars on the bad machine, and I do get a constant video signal when played back on a good machine. The color flickered in and out, so I tried a monochrome crosshatch pattern. It played back with constant video again, and was very jittery both up-and-down and left-to-right, but at least it appears that the heads are recording, so they should be capable of playback also? The head switching point was near the top of the screen which doesn't seem right. I checked the menu settings on the bad machine (and also reset everything per the manual) which didn't seem to fix anything. I took care to make sure the switching point is properly adjusted at 6.5H for recording and 4.5H for playback in the menu adjustments - but I know the software controls can only do so much if the circuit itself is faulty.
So now it's starting to look like an electrical alignment issue. I don't know if anything on the flying REC/PRE board would continue to be suspect now, but I did check those 4 electros with a cheap cap meter - all read around .56 uF though I'm sure the ESR could still be bad. My control signal (30 Hz?) is making it to the slip ring, and the ring and brushes appear okay visually. I do have about +2 volts of DC offset in the control signal, not sure if that would throw off any bias stuff in that preamp chip - and it might be normal anyway. I think it's time I spent several evenings learning some basic VCR theory, studied the manual intently, then set up the bench for a full check of the alignment. I haven't checked the servos yet with the VC93, but the head switching point pretty much stays in the same place and the video playback is consistant on the good machine, albeit jittery. My limited knowledge at this point suggests a problem somewhere in the head switching circuitry and probably more (sheepish grin).
Sounds like an ESR meter is great for in-circuit cap checking? Which one would you recommend? I'll quit for today and let my brain soak up what I've learned so far, then maybe hit it again next weekend. This VCR is more a fun project rather than anything urgent - my chance to learn something about electronics which I somehow manage to do for a living :-)
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