Pioneer CT-F7171 automatic stop failure.

[Kiwick]

Hi you all

I have a 1975 Pioneer CT-F7171 cassette deck i'm restoring, the automatic stop circuit is faulty and i have no clue on what's gone wrong.

When you first hit Play or any other (piano key) button, the stop release solenoid fires immediately.

after 2-3 times, you can engage the play button, but after a few seconds the solenoid fires again, as if the tape has ended (the actual motion sensor works perfectly)

I have recapped the entire auto stop circuit, a waste of time...

Can anyone help me to debug that nasty auto stop thing?

Francesco

 

[markthefixer]

Check the tape presence switch.

Fool it into thinking there is a tape in the well, and see if on play, the takeup reel rotates.

If NOT, Try rotating it by hand to fool the sensor into thinking it is.

If it IS, the tape rotation sensor is probably belt driven, so check the belts, THEN, since it is MOST likely a set of contacts that open and close as it rotates, get some deoxit into the contacts and rotate it a lot.

You can check the presence microswitch AND the tape motion sensor with an ohmmeter of course.

In the 9191 the switch contacts of the motion sensor feed into a pulse discriminator circuit, that when seeing no motion, fires off the reset signals and solenoid.

I agree that the 7171 is different, but there may be commonalities...

 

[Kiwick]

I have tested the motion sensor with an oscilloscope, it pulses correctly and rotates freely along with the counter, but the circuit still fires the stop solenoid..

The CT-F 7171 is an all mechanical piano key deck, and so there's no cassette presence switch.

There are just a few switches operated by the keys for motor power, audio circuits commutation and pause.

Francesco

 

[pustelniakr]

I believe that there has to be a cassette presence switch. If it is not associated with a button in the lower right of the cassette well, it should be associated with the cassette half retainer, in the center of the upper section of the cassette well. I don't know if that is your problem (no experience with this model), but it should still be there one way or other.

Enjoy,
Rich P

 

[markthefixer]

The following is an EXAMPLE:

On the 9191 there is a memory stop switch, which is coupled with the tape counter, when the tape counter hits zero, it does the stop thing.

If this were the 9191, either the circuit is futzed, or the switch at the tape counter is shorted.

 

[Kiwick]

I'll check the memory stop circuit...

Anyway, this is a "front slope loading" deck from 1975, the tape transport is entirely mechanical and operated by clunky big piano keys, and there is no kind of cassette sensing system... in fact, the deck's transport functions will work perfectly without a cassette inside.

I have attached a pic of the deck

Francesco

 

[markthefixer]

The motion sensor switch is part of a circuit that includes C302 (3.3uF 50v), C303 (470 uF 16v) Q301 (2sc735) D301 & D302 and ZD301.

The caps are the first thing I would look at, especially C302. Then be sure C301 has 24 volts across it.

Then check Q301.

AND DON'T overlook SR301, the SCR !!!

 

[Kiwick]

Thanks!

replacing C302 with a brand new one fixed the problem... the salvaged one i used previously was apparently no good... bummer

Francesco

 

[markthefixer]

Makes sense, those little guys dry out faster.