SL-T50
Sony 1983
Betamax SL-T50



beta vcr logo
711B CHASSIS

Technical

SL-T50 rear view
Rear view

Fault and repair guide

The SL-T50ME has the same three video head arrangement as the SL-C9 for noiseless pause and slow motion forward play.

Late model Beta machines made of the black plastic tend to go brittle and shatter. The front of the SLT-50ME machine can crumble, so we suggest at the least keeping it out of direct sunlight. On these later models, the power supply design and layout has also been changed.

pendulum assembly
Pendulum assembly

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.

hall effect sensors with glue
Hall effect sensor attached with glue

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 official replacement but most times it can be repaired, unless the gear is in two pieces or a tooth has broken off. There are two approaches to solve this, either repair the broken gear, or purchase a similar gear and adapt it to fit.
  • Replacement part approach
    • White plastic gears (for RC toy cars) are available quite cheaply on eBay that have 10 teeth, a 2.5mm hole and 5.7mm in diameter and 4.7mm in length.

    In practice the diameter is sufficient and the reduced length does not really matter, just use super glue (or other suitable glue) to glue them to the shaft and protrude the shaft 1mm or so past the end. See: RC-Toy-Car gears

    If you don't need 50 then look for a smaller quantity but the price does not seem to change much.

  • Repair of the existing gear
    • Here is how to repair the shaft when it is out of the machine:
    • Remove the black plastic gear from the shaft and then clean the shaft of all plastic residue.
    • 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.
    • Place the gear in a soft jaw vice such that you can apply pressure to close up the gear crack.
    • 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.
    • Take the gear out of the vice. Take the shaft and put super-glue on it and press the shaft back into the gear.
    • 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).
    • 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.
    • 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.
    • 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.

      Thanks go to Noel Higgins for this fix

SL-T50 head / magnet cover
Head / capstan magnet plastic cover

SL-T50 head / magnet cover in situ
Plastic cover In-situ

Plastic cover

Internally, the head and capstan magnets are protected by a unique plastic cover not seen on other models.


Quick fault guide

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FaultSolution
Explosion and thick white smoke in PSU, the VCR still work perfectlyJust remove, or replace the two 0,068µf 250V capacitors, near the L1 in the power supply.

You can just remove them without replacing, they are not absolutely necessary, they are here only for a basic filtering of the main AC.
Audio or Video input jacks not workingRe-solder the connectors on the board.
No picture and sound on playbackBad solder joints on the black connector of the head amp board (RF-14).
Loading motor stops before threading cycle is completeClean the loading-end microswitch which is located at the top-left hand side of the mechanism.
Tape stuck and won't ejectThe left small gear that's mounted on a metal shaft on the front loading mechanism is cracked. Replace it or try super gluing it. Be careful on the timing of the gears when putting it back together.
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