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Quick fault guide overview
Sony 1983
Betamax SL-C20



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711B CHASSIS

Technical

Inside the SL-C20
Inside view

SL-C20 rear connectors
Rear connectors


Pendulum


hall effect sensors with glue
Hall effect sensor attached with glue

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 cause is usually down to two contributing factors.

The first is the drive pendulum which can cease up 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.
The diagram above shows the pendulum assembly

Stops in play, record and reverse/forward wind

Do not confuse this with the above symptoms. The problem in this case is due to lack of 4.43MHz colour sub-carrier reference in the servo circuit. This in turn is normally caused by failure of silicon fuse PS1 on the YC-25 board.

Patterning on picture

If you experience a patterning on the picture irrespective of whether you are viewing a tape or not then the most likely cause is that capacitor C319 in the power supply has dried up.

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.

Quick fault guide

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FaultSolution
Damaging tapes or tape looping during ejectCheck resistor R420 (3.3ohms) then transistor Q334 2SC10613
Insufficient or excessive colour in playbackCheck resistor R019 (56Kohms) on panel YC25.
Intermittently will not eject-cassetteCheck connector CN608 on the SS16 panel for a poor contact.
No capstan servo lock in recordSuspect failure of transistor Q332 (2SC2458) on panel SS16.
No colourCheck the value of resistors R024 (56k ohms) & R278 (10k ohms) before suspecting capacitor C047, all on the YC25 panel.
No E-E picture after 15 seconds, records in black and whiteAdjust RV009 for 4.3volts p-p at C104 on panel YC25.
No functions or displayCheck 1C001 on the TP37 board
No play, FF or cueSuspect failure of the forward sensor.
No take up / chewing tapesCheck condition & positioning of the pinch roller.
Not erasing previous recordingsCheck for failure of Q503, Q501 then Q502
On/standby switch inoperative and corrupt displayCheck diode D001 on the TM37 panel.
Program display showing -au-Check resistors R063 (120Kohms) & R073 (4.7ohms) before suspecting failure of IC003 on panel TU39
Stopping in rewind / review modeSuspect failure of transistor 0606 (2SC2458) on panel SS16
Switches off shortly after switch onCheck PSU. In particular regulator IC401 (STR1229]) on the PS23 panel
Will not eject cassettes, pinch solenoid not operatingCheck resistor R654 on panel S516
Will not tuneCheck for failure of IC004 on the TU39 board before suspecting the pre-set unit PS001 of failure
Intermittant squiggly patterningPattern is very similar to that caused by C319, but NOT applying to E-E loopthrough. Check Delay Line DL001 on video PCB.
tape not returning to cassette prior to ejectthis is sometimes caused by the gears not fully engaging. press rewind stop then eject.
The machine only laces up half wayCheck and clean Microswitch or replace if necessary.
Will not load / lace or eject tapesWhen attempting to load a tape, the loading motor is seen to stall. This is due a fault in the loading / threading clutch assembly. (Located directly atop the loading motor). The clutch would jammed due to a cracked "sun" gear (the central gear in the clutch0. Replacing the gear cleared the fault.
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