Betamax PALsite: SL-F25 : Technical

SL-F25

1986

Technical

Fault and repair guide

Stops in play or record

This is becoming a more common problem these days. The first thing to check is that there is adequate torque on the take up spool. If there isn't much then the thing to do is to try to increase the foreword torque of the reel motor to compensate for wear. There is an adjustment for this on the servo PCB. This is the lower board in the machine. The adjustment needed is a yellow pot labelled 'FWD'. Turn this to maximise take up torque.

If this fails to fix things then the next thing to try is replacing the pendulum assembly. This is the device that transfers drive from the reel motor to the cassette drive reels. It can become seized with age. Ultimately replace the reel motor bearing. This is moulded into the chassis and so replacement necessitates that the entire chassis be replaced.

One possible compromise is to fit a small piece of plastic into the bottom bearing to raise the rotor and allow it to move freely. Sony supply a repair kit for this purpose.
The diagram above shows the pendulum assembly

No head drum rotation

You may find that the head drum fails to rotate. This is due to a problem with the Hall effect device on the head drum motor which is secured by a blob of glue which tends to become conductive especially if it absorbs moisture. The best remedy is to remove the glue from the device. To do this first remove the rotor from the bottom of the drum by undoing the lock-nut. Sometimes, however, it is enough to wait for the damp to dry out.

Deck goes into rewind

This can be caused by failure of the tape end sensor. You can check this by unplugging the sensor at its socket on the PCB.

Failure to load a tape

This is usually caused by a damaged carriage. However, if you are lucky then it may just be the plastic arm which stops the tape being inserted correctly that has become lose. Look for a white plastic arm on the right hand side of the carriage.

Not recording sound

This is caused by failure of the bias oscillator. Symptoms to look out for are patterning on the video picture. Repair usually requires replacement of the bias transformer and associated capacitors.

Quick fault guide

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Fault Solution

No head drum rotation, no picture (not even from tuner) Check N20 ICP fuse where power supplies enter the main top PCB at the back left.

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