JVC KD-A5 Cassette - stuck fast forwarding

[trgz]

Dug out my old KD-A5 to rip a cassette to my PC, and it appears to be stuck FF-ing (RH take-up wheel spinning). Spins without a cassette in it, and doesn't sense that a cassette stopped winding if one present (motor continues to whirr).
All seems sound mechanically, inside and out, and all the lights on the VUs, all seem good, and there is a light inside the transport section, but the controls to Play/FF/Rev/Rec/etc are not responding. No fuses gone, no cables loose, no caps swollen, just rather dusty inside.
Any thoughts as to where to start to fault it?
(also posted on the r/vintageaudio reddit)

 

[ssid]

I am also working on a KDA5 but don't have that particular issue.
Perhaps the solenoid that controls this is stuck? You might be able to manually move it back?
Could be a logic error on the logic control??
There is a switch sticking out in the tape compartment which detects if a tape is present, that could be stuck on / in?

 

[trgz]

I am also working on a KDA5 but don't have that particular issue.
Perhaps the solenoid that controls this is stuck? You might be able to manually move it back?
Could be a logic error on the logic control??
There is a switch sticking out in the tape compartment which detects if a tape is present, that could be stuck on / in?

Thanks for the reply. My initial suspicions were to the bracket/lever that presses all three (Rec/Chrome(?)/Cassette) switches when ejected, but that (and the individual switches) looks to be operating ok.
I'm going to assume that something must have been engaged, as well as power being supplied to the top motor, in order for the FF-ing to be happening (it looks to move between two drive wheels). I still favour a mechanical issue (dropped in transport?), only as I have more hope in fixing it! . I will look at the circuitry/solenoid controlling the 'Reel motor drive' too - thankfully I have the service manual for guidance (I OCR converted it to help search text and rotated the pages for easier reading).
Good luck with your problem

 

[ssid]

Hi again. Had some thoughts as I am actually working on 3 of these at the moment (my original one which died after recording on it (long story) but now living (playback only) and 2 other spares or repair units of which one I have revived but still things to solve.........

The ff / rw / play mechanism usually only works if the counter belt is running which turns a stator. There is a transistor on the circuit board where the stator sits which could be faulty if it is running constantly. When I had a power supply issues on my decks this transistor heated up and none of the transport controls worked properly. It recovered when it cooled down.

 

[trgz]

Hi again. Had some thoughts as I am actually working on 3 of these at the moment (my original one which died after recording on it (long story) but now living (playback only) and 2 other spares or repair units of which one I have revived but still things to solve.........

The ff / rw / play mechanism usually only works if the counter belt is running which turns a stator. There is a transistor on the circuit board where the stator sits which could be faulty if it is running constantly. When I had a power supply issues on my decks this transistor heated up and none of the transport controls worked properly. It recovered when it cooled down.

Interesting. The counter is definitely counting up, and I see that it's being driven by the take-up spool. This take-up spool appears to be being driven by the reel motor, via the idler, and so my initial logic was to try to figure out why the idler should be engaged with the take-up spool, and what (solenoid?) might be physically engaging it. Naturally, the idler would need to be moved to engage with the rewind. I guess that perhaps a plate/lever must swing it from side-to-side(?), though the motor must be being supplied power as well (unless it's permanently spinning when the machine is on - not implausible). I feel that I'm going to have to start to disassemble it now (but the good weather has me considering leaving it until Autumn!)
Now for a curious twist: when I went looking for this hot transistor (odd, as the machine is very cold) that you mentioned, I was trying to find the PCB it might be on, and I found a small board sat behind the reel motor that I couldn't initially identify in the service manual. It has a couple of connectors, and only few components including L601 & L602 which are not in the KD-A5 (A/B/C/E/J/U) manual, yet mine is a KD-A5B - the backlight is hung off it from points 'G' and 'H' on this board, and the reel motor from 'M' and 'N', so this must be the board called simply 'Connector' that shows IC601 in the manual's diagram, but there's no IC on that board that I can see (and inductors L601/602 are where it ought to be). Oddly, the manual doesn't say what IC601 is. I appreciate this is going off on a tangent, but it's a puzzle
Anyway, I've taken up enough of your time - many thanks