SL-F90
1985
Betamax SL-F90



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Technical

Pendulum
Pendulum


hall effect sensors with glue
Hall effect sensor attached with glue

Fault and repair guide

Stops in play or record

The first thing to check is that there is adequate torque on the take up spool. If there isn't much then the cause is usually down to two contributing factors.

The first is the drive pendulum which can cease up and the second, and the second more serious factor, is wear on the reel motor bottom bearing. The pendulum is simple to replace but the bearing is moulded into the chassis and 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.

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. Full details on how to fix this can be found on the head motor page.

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

The cassette carriage can fail to operate. This is caused by breakage of the plastic gears in the side of the mechanism. When this happens they have to be replaced.

Loading gear and shaft repair

The loading shaft for the Sony has no replacement but most times it can be repaired, unless the gear is in two pieces or a tooth has broken off.

Here is how to repair the shaft when it is out of the machine:

  1. Remove the black plastic gear from the shaft and then clean the shaft of all plastic residue.
  2. Take the gear and pass a hobby knife (or similar narrow blade) down through the gear crack to remove any plastic residue to allow it to close to its correct gap width.
  3. Place the gear in a soft jaw vice such that you can apply pressure to close up the gear crack.
  4. Now use a drill with the same diameter as the outside diameter of metal drive shafts knurled shaft end to clean out the rough plastic residue from the shaft hole.
  5. Take the gear out of the vice. Take the shaft and put super-glue on it and press the shaft back into the gear.
  6. Put the assembly back into the vice again (with the shaft facing down flat, gear top facing up) closing up the gap again but leaving about 3mm of the gear exposed above the top of the vice. (note the gap is facing across the vice gap).
  7. Drill a hole the diameter of paper-clip metal through the top of the gear and shaft but just below the surface of the top disc.
  8. Insert the wire from an unfolded paper clip and turn both ends hard up, then trim off the excess metal. This will lock the plastic gear to the shaft and should keep tension across the gear and not encourage the gap to open up again.
  9. Remove any excess super glue from the cracked tooth gap.
The repaired gear may make a slight noise in operation but that is only an issue when loading and unloading. It puts the machine back into normal operation versus a scrap heap or spares. The pin clears the drive gear by a good margin and prevents the plastic spinning on the shaft again. (by Noel Higgins)


Quick fault guide

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FaultSolution
Ever power on but the display change when pulse on/stand by, not load the tapesBefore of this problem played in b/w with some short white lines
I checked the voltages of the power supply in on and in stand by and all was correct except the 12 volts output, pin 9 of IC001 (STK 5441) and pin 2 of CN002 that ever had about 20 volts
I changed the IC001 (STK 5441) and now load and play in b/w with some short white lines

Is rare that the fuses was not cutted and the video was not damage
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