Sylvania VC2210/ RCA VFT190/193 top loader troubles

[Jeff]

A while back, I took this vcr off someone's hands while it was still working, but then at some point after that, the video output became garbled, so I shelved it. Now that I've come back to it, one of two things happen: the take-up reel spins for a few seconds before it acts as if the stop button has been pressed, or the take up reel will continue spinning, and it will show an image for or a moment or two before losing sync, and it will continue showing the out of sync picture. If I get it to "play" without a tape inserted, the snow on the screen becomes brighter, and blinks on and off, so I know it's not a tape sensing issue. I was wondering if this was worth bothering with, as I tried to find another working vcr with the same chassis to help diagnose, but it appears as though every one I come across is completely dead.

[djfivos]

Hi. That appears to be smilar to the Panasonic NV-2000 PAL model. Looking at the service manual, the take-up spool is driven by an idler wheel that comes in contact with the capstan flywheel during the play/rec mode. Is the idler in good shape?

[Jeff]

The idler wheel looks to be in good shape, but one thing that I have noticed is that with no tape inserted, the take up spool changes speed randomly, but I think that's only because there's no control track for it to read. With a tape inserted, it seems to change it's speed, but it's less noticeable.

[Electronic M]

The take up reel should only opperate at 1 speed in play mode (the take up reel speed unpredictability continuously varies with the amount of tape on the spool so a slip clutch is used to allow the motor to spin faster than the reel and maintain correct tape tension). Only the capstan speed should be controlled by the control track of the tape.

If the belts are not bad you will probably be troubleshooting the electronics. I've seen had electrolytic caps in VCRs a over a decade newer.

[Jeff]

Well... this might be tricky then, as I've already gone through the service manual and looked at the voltages, and they changed accordingly to sp, lp, and slp, no matter where I have the switch. For example, pin 10 of the speed "auto select" IC is 0v when it's spinning fast, (sp) then 10v when it spins slow again (lp or slp) Another curiosity is that pin 12 on that IC shows 6v, which should mean that it's in record sp mode, but pin 13 shows 0v, as if it were in play mode. Pin 13 goes straight to a "record 12v control" transistor, so it looks like the speed control IC is in record mode even though that transistor isn't telling it to be.

[djfivos]

It makes sense if the take-up spool varies in speed with no tape since the play idler is driven by the capstan flyweel, which won't lock at a constant speed if the machine doesn't pick up a control track. Have you cleaned the mode encoder switch?

[Jeff]

The mode switch in this is a slide switch, and it seems to measure good continuity in all positions, although I did give it some contact cleaner.

[Jeff]

I think I got it sorted out... I checked for sound coming from the tape, which sounded okay, so that told me that the control head and speed control circuitry were working fine. That led me to checking the voltages on the "cylinder phase speed control" and "cylinder drive" chips, which all measured fine. Next, I started probing the pulse generator circuit from the cylinder, and found a really bad looking waveform on pin 27 on the "phase speed control" IC. This pin goes through a 100k resistor to a 12v rail and a .33uf capacitor going to ground. I measured the capacitor, and it was only slightly off, but when I replaced it with a .22, the waveform looked better, and I had video. I think this capacitor needs to be .33 uf, because when I added some up to make .3, the waveform and video looked better. I never knew a capacitor drifting from .33 to .51 uf could kill a vcr.