[Takapuna]

Hamish,
The VCR is fitted with the "usual" 3-pole sliding mode switch. However, it moves through all modes properly. The fault I'm chasing is generating a false tape-end signal during FF, causing it to move to STOP and then REW modes. I think the brakes are OK and don't believe this to be a mechanical fault.

Dave,
I agree this fault feels like a grounding, signal pick-up or power rail fault. As far as I can tell, the grounds appear sound. A quick run around with the AVO on Ohmsx1 has not identified anything yet.
Alongside the plug/socket PSU output connections JVC added a supplementary ground wire. It is soldered to the power supply reservoir cap negative leg and has a push fit tag onto one of three blades screwed to the deck mechanism. The other blade connects back to the mainboard as a parallel or back-up to the ground reaching the mainboard from the PSU through the harness. You can remove and replace either or both of these with the deck operating and it makes no perceivable difference to the fault or to machine operation.
As mentioned previously the grounding screw for the deck terminal, complete with star-washer, is essential for end sensor operation. It is the 0V return for the phototransistor. The noise generated by the sensor goes away and FF is maintained without this ground connection. Removing the screw gives the same result as removing the wire from sensor.
I would dig deeper on these end-sensor connections but the tape start-sensor exhibits similar noise problems, albeit to a lesser degree or rather a lower amplitude such that false trips are rare. The start sensor phototransistor is part of the PCB on the cassette cage and receives its connections and ground through a different loom.
I'll remove the mechanical deck once more for a better look at the PCB tracks and connections therein but there's still a number of tracks obscured by motors and mechanism.

Thanks,

Phil
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