Technics RS-TR255 Cassette Decks

Usually the take up reel has a sensor to see if it is spinning. The sensor typically might be a magnetic switch, a simple switch, or an optical sensor. Sometimes these sensors are driven by belt connected to the take up spool. There could also be a function built in to activate a stop mode when the tape counter hits zero. This is so you can rewind back to the same spot on the tape.

On 2/17/2010 12:57 PM bg spake thus:

It's also possible that the end-of-tape sensing is done by simply letting the motor try to spin against the pulleys, and sensing the rise in current as an end-of-tape condition.

Another possibility is that the drive is simply too weak to spin the tape, which could be a result of stretched-out belts, dirty drive parts (belts, pulleys), or (unlikely but possible) stuck bearings somewhere. If it uses the end-of-tape method described above, it will simply give up. I'd try to clean up the mechanics first before looking at other causes.

Thanks ...

I just recalled another detail. The problem drives do auto-reverse. Been so long since I used 'em I'd forgotten.

Uh-oh. That makes the motor again suspect.

One of the units was on a service contract. The record-drive motor was replaced in '94. Possibly relevant if the motor is simply of poor quality.

I didn't dissemble much, but what I saw looked pretty clean.

The playback motor has a part # slightly different from that of the record-drive motor. Safe to assume I could not cannibalize a playback motor to replace a record-drive motor? A fast search indicated replacement motors are no longer available.

Danke, P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

Another common problem is the tape sense switch above the (closed) cassette holder. It's a simple leaf switch, and it is very common for these to get 'sooty' contacts that *just* make when the door is closed, but then bounce and un-make momentarily with the vibration of the heads going in or the mech going into wind / rewind. When the switch un-makes, the system control thinks that the door has been opened, and immediately drops the deck back to neutral, and stops it. Easily proved by shorting across the switch from its terminals at the back, using a screwdriver blade or whatever.

Also, very common for the Technics grey coloured belts to go 'spongy' and lose their grip.

Arfa

my TR- 355 has stripped gears on the REC deck take up clutch. Can't find a service manual or part number, so even if I knew where to get them, I wouldn't know what to order :-( might be worth checking these parts on yours -if the mech senses no take up, it will shut off. But do check the cass-in leaf switches as Arfa says, I have see this problem numerous times, most recently on Sony and Panasonic decks. B

Hi!

If it's not engaging in the recording mode, have you checked to be sure the record prevention safety switch is doing its job?

There should be a small arm that senses whether or not the erase- protection tabs have been removed from the cassette. If the switch or optical sensor attached to this arm aren't working, the deck will refuse to record on a tape.

If it's a switch, you could try shorting across it temporarily and attempting to engage the recording mode. For a full logic deck like the one you have, you will need to have a tape in place for it to work properly--otherwise the tape spill sensor may well shut it down if it starts in the first place. (Most won't operate without a tape in place.)

William

On 2/18/2010 8:30 AM William R. Walsh spake thus:

I don't think that is it: the record-enable switch will (generally, on every cassette deck I've seen) make it impossible to even engage the deck in record mode at all. The OP's description seemed to indicate that the deck would engage when play+record were pressed, but would then immediately shut off as if at end-of-tape, suggesting some other problem.

I just re-tested. Makes no difference whether record is enabled. It does 2 fast clicks and stops, forward or backward. The 2 clicks occur slightly faster for backward.

There are a series of contacts just above the cassette. I cleaned them as best I could with alcohol and Q-tip: made no difference.

Thanks, P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

On 2/18/2010 12:50 PM Puddin' Man spake thus:

I don't think those are contacts; those sound like the springs to hold the cassette in.

I think that he is more referring to the deck by function to identify which one he is talking about in case it makes a difference to the diagnosis, rather than talking about the problem being specifically record-associated.

i.e. the unit has two decks, one of which is a record / play deck (the one the OP is referring to) and the other being play only. This is a common arrangement on dual deck machines, as there is no valid case for having both decks capable of recording.

Arfa

There usually are several sets of contacts, one of which is the cassette sense switch, the others being for sensing the record prevention tab (at left side), and auto tape-type detection (right centre). Are you sure that you actually got to the contacts ? These leaf switches normally have a clear plastic cover over them, and it is necessary to remove this to clean them successfully. This often involves withdrawing the pcb that they are soldered to. When you can genuinely get to the contacts, they are best cleaned by drawing a piece of paper soaked in switch cleaner through them, whilst keeping some tension squeezed on them.

Another place that you might look is on the main body of the deck. I can't remember if Technics decks have this additional switch or not, but many decks do. It is another leaf switch, but usually an open type, and somewhat smaller than the cassette sense switches. It is operated by the top edge of the head plate pressing on it as the heads go fully in, to inform the system control micro that the loading sequence has completed. These switches often go intermittent like the sense switches, and again give the same symptom of the deck going through the loading sequence, then dropping back to neutral before the tape starts to transport.

Arfa

I own a pretty high end Sony dual and only deck B records. I don't recall one that records on both like you mention there is no need.

Quite so.

Arfa

Much thanks for numerous responses.

It looks like I'll have to attempt to dissemble a dysfunctional drive. Without schematic or other doc.

Other bonfires have taken precedence. I dunno when I'll be able to get back to the "Lazarus-From-The-Dead" cassette project. :-)

But your help was much appreciated, and, with luck, may yet provide the needed guidance.

Cheers, P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."