Toshiba V854 VCR

[Michael Maurice]

This should have been a nice easy one for me, replace belt, clean mode switch and return to the customer.

Alas no

If you insert a tape which is not at the beginning, it plays fine, it also rewinds and fast forwards.

However if you put a tape in which is at the beginning, ie clear leader then it just ejects itself.

I've checked the LED and IR detectors for dry joints but the fault remains.

Any clues?

[Welsh Anorak]

Might be a stupid suggestion, but have you tried it with the top case on?

[Michael Maurice]

I put thick cardboard on the top but can check it with the covers on.

[Welsh Anorak]

Trying to think what real life situation would cause this. Usually the only time a tape ejects when not asked to is when you press record on a protected tape - not applicable here. Might be worth winding a tape to the end and see if it auto-rewinds, then stops without complaint when it gets to the start. That would eliminate the end sensors/IR.

[Michael Maurice]

With the machine in as near darkness as i can get.

When the tape gets to the end in play or FF, it rewinds. When it gets to the beginning, it stops then ejects.

If you put a take in and press any button, it ejects.

I've checked the mech timing and its spot on, though i wouldn't expect it to be that anyway.

[Philips210]

Just wondered if the customer reported that fault or did it come about after servicing work?

Regards,
Symon

[John123]

If the belt had perished it's possible the machine hadn't been used in a very long while, and the mode switch contacts might be excessively tarnished from sitting idle. Perhaps try pulling the switch apart and thoroughly cleaning/ re-tensioning the contacts.

[Michael Maurice]

Originally Posted by Philips210

Just wondered if the customer reported that fault or did it come about after servicing work?

Regards,
Symon

The customer reported that when he put a tape in, it chewed it up. So yes it seems to have occurred after being serviced.

Originally Posted by John123

If the belt had perished it's possible the machine hadn't been used in a very long while, and the mode switch contacts might be excessively tarnished from sitting idle. Perhaps try pulling the switch apart and thoroughly cleaning/ re-tensioning the contacts.

I've already done that, (see post #1)

[Red to black]

These machines are normally pretty well behaved, a few cast Ally levers and a couple of carriage gears aside
double check the mechanism timing to the mode switch, even one tooth out can cause forward spooling problems to cover the end sensors past the clear leader tape(brakes not coming off properly ) which causes this type of problem.

[ben]

I seem to remember a Television Test case or fault report with a Philips Charlie deck that did this (not engaging auto FF sequence when fully rewound). Think that may have been sticky brakes. Will have a think!

[Welsh Anorak]

From what you say, if you were to cover the right end sensor I assume the machine would work correctly, except for stopping at the beginning of a tape, of course. So it has to be something to do with the machine thinking you've fed in a broken tape. Therefore what R2B says must be correct, in that the machine isn't spooling on slightly when a tape's inserted to pass the leader. Does it even try to do that in case Ben's theory is right about the brake holding it back?
The annoying thing is this all points to mode switch which is fine. In an ideal world you'd just change it to be sure, but of course you're unlikely to find one.

[Michael Maurice]

I've checked the timing and its spot on, in fact you cannot mistime it.

I've checked the mode switch and its ok.

If you cover the RH sensor, the tape plays normally as does the rew and ff, but obviously wont stop as it should at the beginning of the tape.

The brakes are working correctly.

What next?

[Welsh Anorak]

This is puzzling.
As far as I can remember, the tape comes to the end on rewind then stops. The question is should it then eject if all was well?
It clearly thinks you've put in a casette with no tape in it and throws it out. Does it even try to shuffle the tape forward slightly to get past the leader or does it immediately eject?
Another silly suggestion, but have you tried it with several tapes?

[Philips210]

Hi.

As Glyn pointed out the only real situation where you'd expect an automatic eject operation would be if a record protected tape was put in the machine and record function selected. Might be worth checking the deck record protect switch and associated circuit.
I don't know how the logic control works on this machine but wondered if it is recognising a spurious eject command possibly due to the front panel tact switches or leakage in the switch matrix? I remember having a leaky diode on the control panel in a Thomson TV that caused very confused operation which defied normal fault diagnosis.
I might be inclined to unclip the front panel and check the switch functions.
Just a thought.

Regards,
Symon

[Welsh Anorak]

I agree Symon, but Michael says that if a tape is inserted that's not at the beginning the machine works perfectly. That would tend to eliminate the front panel, though it's worth a go. This is a real puzzler!
I have had end sensors giving inaccurate signals to the micro but I feel I'm clutching at straws here.

[Michael Maurice]

I also covered up the end sensor and it worked ok. I will have to take scope checks when I get time

[Red to black]

I now personally think you have either EOT sensor system problems, electronic or otherwise, or as another poster mentioned record protect switch problems, there was also a couple of updated uprocessor issues with this series of machines, most of this was to do with the modulator output frequency setting range and PDC/videoplus ,auto clock setting though.

[Michael Maurice]

I have replaced both EOT sensors but the fault persists.

If you rewind the tape, it detects when it reaches the beginning of the tape, but it doesn't move it forward.

If you wind the tape forward by hand, so that the leader is right inside the cassette it works.

If you put a prerecorded tape that has been wound on, it goes straight into play.

If you put a normal tape in that has been wound on, it goes in but remains in stop mode until a function is selected.

I have run out of ideas, I have boxed it up ready to return to its owner with the caveat about winding the tape on.

That is unless anyone can come up with a bright idea about what can be done to repair it.

[ben]

Still trying to puzzle this one out. I fully understand your frustration!

Without knowing how the circuit works in this unit, it is hard to get further with this. A service manual's circuit description is needed.
The last time I worked on a circuit that performed this function it was a logic gate using a monostable and a timing capacitor.

With rewind motor energised (flip flop set), the following occur as tape start is sensed by EOT detector going low (AND gate):
-Brake sequence (Rewind flip flop Reset)
-Reversal of tape motion to ff (end stop flip flop Set)
-Winding for approx 1 second (timing cap)
-Brake sequence (stop) end stop F-F reset as cap discharged.

Clearly in your case only the first part of the sequence is happening. The tricky part is finding out which IC is responsible for this logic. My money is on a duff cap on one of its outputs. I suppose we'll never know!

If it were mine, had no other solution and I had the time I would knock up a small circuit with a 555 IC with timing cap, connected between the ff line to the deck's control IC plus EOT line, so that when the RH EOT line went low during rewind it would kick the deck into FF and peform the sequence above! I appreciate this is a paid repair so no use in this case

[Red to black]

Having said all of what maybe wrong, some of these Thomson designed machines( Tosh V3/Thomson R 4000 onwards) did have some problems with their micros, mainly to do with PDC/Video plus and auto clock setting, they also had some POS/hidden "demo modes".
Probably B.E.R if it is the Tosh developed TMP series micro though, as I don't know if either a) still obtainable, or b) if it would be worth it now.