Autoreverse / play issue on deck

[Bert Beukema]

Hi guys,

First off: i hate modern cassettedecks for servicing. That off my back, on my desk is the old deck from my father. It's a Philips FC-910 double deck with one play and one autoreverse deck. The play deck is doing it's job but the autoreverse deck is faulty. I've changed the belts as a generic measure, doesn't help with the issue. This is a machine that uses a solenoid.

All functions are OK on the autoreverse deck but the actual play function. When one presses play, it will start playing (and produce sound) but after 2 seconds it will autoreverse and play for another 2 seconds. Then it stops. There are no errors on the base voltages; the motors are working fine and everything is lubed and ready to go. There are no broken gears and manually I can move all components with ease. I can see the solenoid moving; not sure if it is moving correctly though.

Troubleshooting is a damn pain on this machine. First off, the PCB that controls most of the motor functions is double sided; with the reverse side all SMD components that are *unmarked*. Yep. No silk screening. I do have the service manual, which is actually superbe. I've added some parts of the service manual as an attachment. As far as I can see most of the circuit involving the deck is on the SMD side.

In no way am I an experienced cassettedeck technician; my forte is on receivers and amplifiers. That said I would like to take a stab at this if the cool cassettedeck guys think there is a possibility of resurrection. That said, I'm not going to spend days with this deck ;-).

Thanks!

Bert

 

[Bert Beukema]

So, this morning I had to wait some time for another project. I decided to dismantle the deck to get at the PCB inside it. The service manual isn't very clear about that PCB. In reality there is a horizontally mounted PCB to which a vertically mounted PCB is attached. This vertical small PCB goes behind the left mounting gear / carrier.

When dismounting the left gear I could see what was on the PCB; it was a NJL5165K photo reflector. This is what is used to check the end of the tape. It does so by emitting light onto the back of the left gear / carrier which has reflective material on it.

I could see that the back of the gear was very dirty. I cleaned the gear and the reflector using Isopropanol. Then I rebuilt the deck and lo and behold: everything works as it should! So, if you are using any deck that uses a reflector for autoreverse, check to see if the reflecting surface is still clean.

 

[dr*audio]

I think you are on the right track. The reel is part of the motion sensing circuit. It puts out a varying voltage as long as the reel turns. Look at the output with an oscilloscope and see if you have a varying voltage.

 

[Bert Beukema]

Scoping the unit shows voltages are fine, they actually always were fine even for the few seconds it turned before fixing the unit. It now plays as it should so it's always a smart thing with these decks that use some sort of sensor unit to check if the sensor itself can actually 'sense' something. In this case the reflective material behind sensing gear was essentially black from buildup of crap, after cleaning it was silver again. And the sensor behind it could do it's work.