Sony 1979
Betamax SL-C7

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SL-C7 inside

Camera Socket

The 14 Pin Camera socket is known as a Sony K-connector. Details of the pin connections are available online.

Fault and repair guide

No E to E sound

For no sound from the tuner check the TBA120 FM demodulator IC

No Playback Audio

Suspect the audio change-over relay on the AS-3 board.

Problems setting clock or timer

The switches used on the clock and timer section are prone to failure. When they begin to stick they can cause all sorts of erroneous behaviour. The only reliable cure is to replace them.

Machine stops intermittently in rewind

Check that the APS and or memory function is not switched on.

VCR is sluggish in or fails to rewind

Internally the C7 contains many drive belts which are used in the mechanics of tape transport. With age these belts become slack causing malfunctions and when this happens the whole lot should be replaced. In particular for the rewind function you will need to replace a tyre on the supply reel. A 'rewind' kit of replacement parts is available from many sources. The Sony part number is A 670634A.

Strange behaviour of capstan or drum servo

The first thing to check is the tantalum capacitors in the servo circuit. Look for the 2.2 micro farad ones first.

Sluggish threading and capstan problems

The bottom bearing on the capstan motor is prone to wear and because this motor also drives the threading mechanism threading can become sluggish. When this happens you will hear a horrible squeaking noise! It is possible to strip down the motor and replace the bearing but an easier option is to replace the entire motor if you can find a replacement.

Picture drops out in playback

This can be caused by lack of CTL pulses from the Audio/Control head. One remedy is to modify the CTL amp circuit to give it more gain. Alternatively a worn head can be 'polished up' to prolong its life.

Quick fault guide

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Black line appears during light / dark scene changesCheck the setting of pre-set RVI on the.NC1 panel also check resistors-R96, R330/1 & capacitor C264
Capstan speed variationCheck the value of resistor R68 [10k ohms] then check 1C3 ITC40111 & 1C12 [M58478P]
DeadCheck fuse F006 for o/c then check PSU. transistors 0101, Q102 [2SC23351, surge resistor R101, ICI tTL494CN], diodes D201/2, D101/4 a capacitors C110/1. a modification kit is available from Sony if PSU transistors fail regularly
Dead, fuse F004 blownReplace fuse F004 with a higher rating (this fuse tends to go o/c with age)
Ejecting tapes at switch onCheck transistor Q2 & diode D6 in the microcomputer reset circuit
Int / no channel changeCheck for correct operation of the clear switch S20 then suspect logic gate 1C7, if the channel display changes check 1C003 [CX7611] on the CE3 board for failure
Intermittent or no sound in tee e-e modeCheck capacitor C521, if ok then check ICS03 [TBAI2OB] for failure
Intermittent or no timer programming or operationCheck switches S002/S020 on panel TM10 for dirty contacts if ok check IC007 [UPD408IBI and IC008 [TC4071BPI on panel TMIO before suspecting 1C009 [TC4069] / IC001 [MB-8841-18OJ]
Intermittent or poor soundCheck relays RY401 and RY402 on the AS3 board for failure
Intermittent clock operation or all LEDs litSuspect IC7 (TC40111) then check IC1 [CXBO4] transistor 03
Intermittent sound and picture muting in playbackCheck the audio / control head for contamination or wear
Intermittently stops a rewinds, tape end alarm bleeps, machine shutdownCheck the tape end sensor head on the SY11 board for dry joints then suspect failure of 1C8 [BX3421]
Will not load tapesSuspect dry joints on diodes D710 & D712 on the SJ1 panel
Interference on picture in e-e modeCheck settings of the AFC & AFC offset on panel YC6
No or poor capstan servo lockCheck IC2 [CX143] on panel AS3 for failure
No channel lock or tuning memoryCheck tuning chip 1C4 [CX76OE] then memory chip 1C3 [CX761A]
No colour in playback & e-e modesSuspect failure of IC6 [CX1301]
No functionsCheck regulator transistor Q25 [2SC13641] zener diode D)gon the system control panel
No picture in playback, pause search modes okCheck transistor Q28 [25C1364] on the AS3 board
No playCheck capacitors C2, C3 & C4 on the SY11 board
No servo lock in recordCheck the switching transistor Q25
No sound or picture in e-e, record or playbackSuspect failure of transistor Q423 on the AS3 board
No tuner outputCheck the tuner switching transistor 06511 on panel PCI
No voltage to motor in rewindSuspect coil L1 of o/c
Playback picture breaks up when warmSuspect intermittent failure of 1C1 [CX134A] on panel RF2. Test by freezing.
Poor picture sync in playbackCheck capacitor C021 for failure
Slow motion and frame functions do not work in pause modeCheck capacitor C701 on panel SJ1 for failure
Stuck in rewindCheck coil L2 on the SY11 panel for open circuit
Will not tuneCheck fuse F006 for o/c then 1C4 [CX76OE] for failure
Suspect failure of IC6 [CX1301]Suspect failure of IC6 [CX1301]
Stops in play mode oftenPlay tape and look at the tape tension check arm. If the tape is slack, check FWD take-up torque. Could be belts and gear, clean/replace.

Take-up torque tends to increase gradually due to ageing. Change out FWD idler (gear on small belt left above the right winder)
Tip: take out idler, slightly push in and check friction.
No Tracking, noise appears every few secondsOn AS-3 board, replace IC3 (TC4011bp)
APS (Index) is faulty (affects REW/FF functions with APS on)On AS-3 board, replace IC5 (TC4011BP)
Horizontal picture jitter in playback - drum servo not stableIf TP2 on the AS3 board is a square wave at 1/2 frame rate instead of a steady 5.2v, then you may find C11 (0.47µF) on the AS3 board (near IC1 pin 11) has gone high. Even a slight increase can extended the time constant on IC1 pin 11 causing the 'one-shot' timer (gating filter) to miss alternate Servo Ref (frame sync) pulses on TP13, causing the 'triangle' error reference waveform at TP6 to be at HALF its correct frequency. The speed error signal then effectively changes sign every other frame and the drum servo hunts up and down hopelessly, causing the horizontal picture jitter. dB 12/02/11.
Flutter on audio PB - tracking loss every few seconds - capstan servo unstableCheck TP4 on the AS3 board. Should be a (fairly) steady 5.5v. If it jitters, check C41 on the AS3 board. Should be 0.33µF, if it's gone high the 30mSec monostable (built using IC3) can exceed 40mS and drop cycles. IC3 pin 4 should be a steady square wave, roughly 30mSec high, 10mSec low.
PSU FailureC110 & C111 failed and replaced. Replaced TL494CN. Replaced Q101 & Q102 (transistor is C2335 - couldn't obtain replacements - used BUL510 instead). R101 appears to be labelled as 3W 3K3 - it is infact a 3.3R resistor. Using a 3K3 caused TL494CN to go into a safe mode.
Tape lacing failureCheck that the tape lacing carriage position sensor (microswitch in top left corner) and its lever isn't seized. Also check the actuator arm that moves the tape against the tracking head is not seized also.
Rewind and review fail to functionBlue Sanyo electrolytic capacitors(1µF, 0.47µF, 0.33µF) replaced on SY-10 and SY-11
No Tracking, noise appears every few secondsOn AS-3 board replace C041. 0,33µF
no ctl when playingchange R 123 to a 2k7ohms value
drum servo and capstan all over the placeC11 0.47µf is the usual cause, also as already mentioned C41 0.33µf is worth replacing whilst there.
Tact switches for SL C7 timerThese are a perfect fit. Cut 2 of the four pins and fit crossways into the holes.
No colour in a thin vertical bar on the right edge of the pictureAdjust the AFC pot on the YC-6 board on the bottom. If you adjust it too far you lose all colour.
Audio noise in stop modeChanged unstable C-403 in mic amplifier.
SLC7 No colour on playbackBPF1 open circuit. If replacement is not available, a 180pF capacitor works very well instead.
Wont Switch on unless timer program 1 is selectedCheck D106 for open circuit on TM11 Board.
No Color or not locked or intermittent with horizontal stripesAPC loop. Check and replace C144, Q97, IC6, and C150 (0.01µf) in sync separator of IC5 open circuit.
No recorded / e-e sound (but OK with pre-recorded tape)If sound is good with a prerecorded tape but there's no
E-E or recorded sound check the voltages around the
TDA12OUB sound i.f. chip (TBA120UB). If there's no voltage at pin 14
the chip is faulty. pin 14 gets its voltage via an internal
resistor. Use a 10m ohm resistor from pin 14 to pin 11, to save replacing the chip. James (
Clock not working - Battery damage to the PCBThe timekeeper battery is a 1.2v rechargeable unit, often leaky. This destroys the traces of the pcb. I should have replacement bare PCBs by the time you read this if anyone needs one.

The battery should be taken off the board, and replaced with a 1.2v 500mAh unit, or use a standard rechargeable AAA battery in a holder, and mount away from the circuitry for easy future replacement. James (
No Colour and bad picture wobble / syncPlayback in b/w, with a loss of sync. Replacing IC6 restored the colour, although the picture was still having issues with breaking up. Replacing IC5 returned everything to normal.

c150 (0.01uf 50v) & C159 (1uf 50v) in the sync sep counter circuit also changed as out of tolerance. I changed these at the same time as IC5, so perhaps do this before swapping out IC5. I doubt the capacitors were the issue though.
James (
Slow to eject / load (or fails to load)Replaced the loading / capstan motor, double checked the power trail, and stripped the machine down again to ensure everything was free and smooth.

It turns out I'd misadjusted the top guide on the loading ring, causing it to be a little tight - even though by hand it all seemed to load smoothly.

Lesson: never overlook the obvious.

James (