Troubleshooting erratic tape tempo -- Pianocorder Forum

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Subject: Troubleshooting erratic tape tempo

Author:
Tom Lear

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Date Posted: 20:05:43 03/23/04 Tue

Pianocorder trouble shooting information.

Pianocorder erratic tape tempo (speeding up) due to high resistance in the tempo control circuit.

There are two sources of possible high resistance in the tape tempo control circuit.

1) High resistance in the external tempo control jack. The jack has three contacts, two of which are switched, they are normally closed. Because the jack is never used, over a long period of time and probably affected by atmospheric conditions, the contacts may develop high resistance. The higher the resistance, the faster the deck will run. Of course, it's totally erratic and uncontrollable.

Simple fix. Spray contact cleaner into the jack and shove a 1/4" phono plug in and out a bunch of times. If the jack is resistant to this fix, then:

See page 93 of the schematics. Schematic of tape deck PC board. See on the lower left - external tempo control. If you have to go into the deck to correct the problem, then all you have to do is jump J119 and J118.

2) High resistance in the record switch.

When the Pianocorder is in the play position only and record position is never engaged, the switch just sits in one position all the time and doesn't get cleaned by the rubbing action that would normally occur when engaging record. The fix is to push down the record switch a 1/2 dozen times to clean the contacts. (Place a blank tape in the deck and depress and release the record button a 1/2 dozen times.) Normally that should fix the problem. In a more severe case, it would require opening the tape deck to get to the switch (on the PC board) and treating it with contact cleaner.

More about high resistance in the record/play switch..
If there is any question about high resistance in the record-play switching, you can jump the switch if you are not using the record function. Jump pins J118 and J108. (Even if you are using the record function, it's OK, just remember to set the tempo control at midway when recording.)

Note that jumping between J118 to J108 will take the external tempo jack out of the circuit too, so both potential sources of high resistance in the tempo speed circuit are eliminated with one jumper.

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