Cassette tape component

[Puddin' Man]

This was thread "Technics RS-TR255 Cassette Decks" back in Feb., 2010.
Again, thanks for helpful responses "way back when". I come again
begging advice.

I finally found time to putter with my 2 units. In a nutshell, they are
dual decks with a playback/record/auto-reverse deck and a playback-only
deck. On both, the record, etc deck starts to play, then immediately stops.

The fact that I don't *really* know what I'm doing is here deemed to
be "A Mere Detail".

When tested for playback or record, a little .5 x .5 x 1 inch component
on the back of the tape drive, with many, many copper windings, and a
metal shaft in the middle (connected to a plastic actuator) kicks in,
then kicks right back out, evidently preventing the machine from
functioning. Some pics are here:

http://yfrog.com/cbcassetteswitch2j
http://yfrog.com/bhcassetteswitch3j

Is it a switch? Is it a solenoid?

I'd dearly, dearly hate to have to consign -both- cassette machines to the
trash bin. If there is any hope for, say, replacing or re-building the
offending components, I'd much appreciate hearing about it.

Thanks,
P

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

 

[Puddin' Man]

It's the cam control solenoid. Works the latch that releases the cam gear to
allow it to be driven to its next phase.

Many thanks. These things can look strange if you've not seen them
before.

As to the fault, check any tape
presence sense switches that it may have - normally 'leaf' types in a clear
plastic protection 'sleeve' mounted at the top edge of the deck,

There's about 5 of 'em, 2 for write-protect and 3 for <???>. I ran compressed
air thru, but couldn't figger how to get the plastic cover off. The
copper leaves *look* OK, but ...

Do you know ... do the plastic covers just slip off, or does one
need to unsolder, or ???

and also
check that the belt which drives the take up spool is good. It's very common
on Technics decks for that belt to go 'elastic' and slip.

I'd better just replace that one. Might take a while to find a
replacement.

Thanks,
P

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

 

[Puddin' Man]

Auto tape-type detect, that sort of thing. You might also find another
rather smaller and 'open' one on the main body of the deck, that is there to
detect when the head plate has reached the end of its travel in the 'heads
in' position.

Yes, found the head-plate sensor.

I ran compressed

The contacts get 'sooty' and need cleaning by pulling a piece of paper
soaked in isopropyl alcohol or switch cleaner through them.

Can be either. The covers are pretty much always 'clipped' on by a tiny
dimple at each side, but the trick is that in order to slide them off, they
sometimes need to be clear of the deck metalwork. Sometimes they will come
off simply by being 'firm' with them and wiggling, but sometimes, you need
to slip a thin scalpel blade or similar between the switch body and its
cover.

4 little dimples per switch. I baby-ed 'em, nursed 'em, spread 'em open
a tad to ease the cover off, and many dimples broke anyway. Old, brittle
plastic. Got the clear covers off, but they won't re-mount, just hang
loose and rattle-y.

Ran a jewelers file thru the contacts, then cleaned 'em with the contact
cleaner on paper.

If the switches are causing trouble, the deck usually cuts out very
quickly after starting, as the vibration of the heads going in, 'rattles'
the switch and makes its contacts momentarily fail, which the system control
micro then interprets as there being no tape present, so shuts the deck back
down to 'neutral' so that the door interlock will be released. If the heads
go in ok, and the deck runs for a few seconds - possibly even actually
playing the tape correctly (music-wise) - then this is usually due to
failure of the take up spool to rotate. The system control allows a few
seconds for this, as cassette tapes can get tight, and the take up run a bit
erratically. They try to produce a compromise between allowing a tight tape
to be played, and not producing too large a tape loop, if the take up spool
is genuinely not going round at all. You can force the deck to run by
locating which of the leaf switches is the tape presence detect one, and
shorting it, or holding it up with your finger. On a Technics deck, you may
need to have the inner door frame closed for the deck to run, but you can
have the outer door trim removed to get your finger in. You should then be
able to see the take up to check if it is running, and see why not, if not.
You can also check that the torque at the spool is sufficient to run the
tape.


You should be able to see or 'feel' if the belts are bad. Suspect the take
up drive belt particularly if it's one of the Technics grey ones.

The belt is black in color and doesn't appear to be the problem.

I put it back together sans plastic covers and re-tested. Same result.
No evidence that the leaf switches are the problem.

Many symptoms seem to point to a faulty motor, but it's curious. The
playback motor was working. When I swapped it into the record-deck, I
also got the same result (just 3 clicks, then nothing).

If you can think of anything else, I'm all ears, but as of now, the score
is as follows:

Matsushita: 2 (assuming I'm forced to pitch both units)
Me: zero :-(

In any event, you've been extremely helpful, and it is -very- much appreciated.

Prost,
P

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

 

[Puddin' Man]

It's very unusual for these motors to fail totally, and I would be surprised
if you were unlucky enough to have experienced two under the same roof. Time
for some more detailed observations, I think.

*Exactly* what happens when you attempt to play ?

Exactly 4 clicks. Solenoid plunger pulls in, comes back out, pulls in again,
comes back out again.

Any motor movement at all ?

None perceptible.

What about if you try other functions such as wind or rewind ?

Same as 'play' above.

Have you managed to bypass the tape presence switch ?

I dunno which it is. There are 3 for which I cannot trace the circuitry.
But I confirmed that all switch circuits were closed except for the
sensor for plate height (head position). When I short that
one, the solenoid actuates.

Have you tried 'working' the deck by hand i.e. press the solenoid plunger in
with a small screwdriver tip. You should see the cam gear 'unlock'.

I can't see the gear without dis-assembling the drive components (again).

Then rotate the forward capstan (left as you look at the back) clockwise
(viewing from the back). This should cause the cam gear to rotate to the next
phase and relock.

I can hear it click.

Probably "fast forward", but might be
"play". You should be able to do that for all four phases, and make sure
that the deck is doing what it should be mechanically at least.

Not sure I follow that.
When I continue to rotate, I get additional clicks. After 2, the cassette
won't come out. After another click it will.

Major (weird) news. You'll recall I have 2 RS-TR255's, call 'em A. and B.
I've been working on A. Thought to check something on B. to see if it
was same as A., pulled the cover, tested playback, and it worked. It failed
per A. less than a week ago. Also does reverse play, FF, etc.

There are 4 gold screws on the drive plate on B. that are absent on A.
Looks like they just keep the big wheel from coming off (but it's shaft
does that). I thought to install the 4 screws on the A. unit, but it
wouldn't take 'em: screw holes *look* the same, but they aren't
threaded as on B. I double-checked, both A. and B. are RS-TR255's.

Strange, eh? Well, at least I won't be chucking B. in the garbage for
a while. I even got readings on the vu, so I guess it's working (for now).

Thanks,
P

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

 

[Puddin' Man]

With no tape in place, the deck should do nothing - no clicks, no motor
movement, zip, zilch, nada. Now, if you press each switch up in turn with a
finger tip, one of them should get the deck doing something - even if it's
just the solenoid clicking behaviour. The switch that you had to press to
get that, is the tape presence switch.

There are 6 leaf switches on top of the tape slot. 5 of these look identical
and have plastic covers, the other is shorter and is exposed (no plastic
cover). This last one senses the head-plate being raised. It fires the
solenoid when jumped. None of the other 5 seems to actuate anything with the
manual test you described. I tested on both units.

You don't need (or want) a tape in place to work the deck by hand. You don't
want any power applied either. The cam gear should have four phases. That is
"stop" or neutral, "FF", "Play" and "Rew". The periphery of the cam gear has
four positions with missing teeth that correspond to each of these phase
positions, and four raised latch catches on the surface, which also
correspond. The lever worked by the solenoid, catches on these latch
positions in turn. The cam has a bias spring to keep it pressed against the
latch lever. Suppose the cam has the deck in the "stop" position. The
missing teeth in the cam gear periphery which correspond to that position,
will be over the drive gear which is at the centre of the forward capstan.
So the capstan can freely rotate, without driving the cam gear. When the
solenoid is activated to select a transport mode - say "FF" - the latch will
disengage, and the bias spring will start to rotate the cam gear, until the
tooth-free area has moved around, and the next section which has teeth, has
engaged with the gear at the centre of the capstan. By this time, the motor
should be running, and driving the capstan. This, in turn, will drive the
cam gear round until it reaches the next area where teeth are missing. This
will stop the cam in the new position, and the solenoid latch will drop onto
the catch at that position on the cam gear surface, and hold the gear at
that position, again against the bias spring. At this time, various levers
running in grooves under the gear, will have moved their positions to work
what ever bits of mech that they have to i.e. moving reel idlers into place
and disengaging reel brakes etc.

Thanks. That helps a bit. I still can't see it happen, but your description
seems to "cover the bases".

That is odd. The 255 does not appear to be a model that was valid in the UK,
so I can't get data for it off the Pan engineering website. There is a 155
on there, which might be pretty similar. Have you checked for voltage at the
"+" terminal of the motor when it should be running ? The motor should have
4 terminals. "-" is common to chassis, "+" should have switched 12v on it,
and "A" and "B" are the speed control terminals

I measure ~12v dc from the chassis to one of the contacts when I 'play'
a tape.

Just checked. The service manual for the 155 is the same as for the 255

If it is available and doesn't cost a bundle, would appreciate a link
to where I can find it.

Thanks,
P

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

 

[Puddin' Man]

You have to press a function button at the same time. Your finger is
'pretending' to be a tape ...

Sorry ... my mind was elsewhere.

I have it now. It looks strange, all 5 switches *appear* to close
whenever a tape is inserted.

Have you checked for voltage at the

If the ground to the motor is good, and 12v 'appears' on the "+" terminal of
the motor when a function button is pressed, then I'm pretty sure that on
those motors, they should run, regardless of what's going on on the "A" and
"B" speed control terminals. You could try disconnecting the motor ribbon,
and feeding an external 12v from a power supply directly to the motor, and
see what happens.

I looked a bit for a handy-dandy live 12v supply that I could get my big,
clumsy alligator clip onto for a jump to the motor, and didn't find anything
suitable.

I suppose I could rig an old pc power supply, but ...

Is the email address that your post was sent from - with the "DOT" changed
of course - valid ? If so, I'll send it to you. If you would prefer it to go
to a different address, mail me off-group at the address I used to send
this.

Yes, it is valid. Just substitute . for DOT and it should work OK.

Many Thanks,
P

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