SL-C7
1979
Betamax SL-C7



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Technical

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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FaultSolution
Black line appears during light / dark scene changes. Check the setting of pre-set RVI on the.NC1 panel also check resistors-R96, R330/1 & capacitor C264
Capstan speed variation. Check the value of resistor R68 [10k ohms] then check 1C3 ITC40111 & 1C12 [M58478P]
Dead. Check 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 blown. Replace fuse F004 with a higher rating (this fuse tends to go o/c with age)
Ejecting tapes at switch on. Check transistor Q2 & diode D6 in the microcomputer reset circuit
Int / no channel change. Check 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 mode. Check capacitor C521, if ok then check ICS03 [TBAI2OB] for failure
Intermittent or no timer programming or operation. Check 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 sound. Check relays RY401 and RY402 on the AS3 board for failure
Intermittent clock operation or all LEDs lit. Suspect IC7 (TC40111) then check IC1 [CXBO4] transistor 03
Intermittent sound and picture muting in playback. Check the audio / control head for contamination or wear
Intermittently stops a rewinds, tape end alarm bleeps, machine shutdown. Check the tape end sensor head on the SY11 board for dry joints then suspect failure of 1C8 [BX3421]
Will not load tapes. Suspect dry joints on diodes D710 & D712 on the SJ1 panel
Interference on picture in e-e mode. Check settings of the AFC & AFC offset on panel YC6
No or poor capstan servo lock. Check IC2 [CX143] on panel AS3 for failure
No channel lock or tuning memory. Check tuning chip 1C4 [CX76OE] then memory chip 1C3 [CX761A]
No colour in playback & e-e modes. Suspect failure of IC6 [CX1301]
No functions. Check regulator transistor Q25 [2SC13641] zener diode D)gon the system control panel
No picture in playback, pause search modes ok. Check transistor Q28 [25C1364] on the AS3 board
No play. Check capacitors C2, C3 & C4 on the SY11 board
No servo lock in record. Check the switching transistor Q25
No sound or picture in e-e, record or playback. Suspect failure of transistor Q423 on the AS3 board
No tuner output. Check the tuner switching transistor 06511 on panel PCI
No voltage to motor in rewind. Suspect coil L1 of o/c
Playback picture breaks up when warm. Suspect intermittent failure of 1C1 [CX134A] on panel RF2. Test by freezing.
Poor picture sync in playback. Check capacitor C021 for failure
Slow motion and frame functions do not work in pause mode. Check capacitor C701 on panel SJ1 for failure
Stuck in rewind. heck coil L2 on the SY11 panel for open circuit
Will not tune. Check fuse F006 for o/c then 1C4 [CX76OE] for failure
Suspect failure of IC6 [CX1301]Suspect failure of IC6 [CX1301]
Stops in playmode 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 aging. 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, nois appears every few seconds.On 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 (0.47uF) 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 0.33uF, 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 siezed. Also check the actuator arm that moves the tape against the tracking head isnt siezed also.
Rewind and review fail to functionBlue Sanyo electrolytic capacitors(1uF, 0.47uF, 0.33uF) replaced on SY-10 and SY-11
No Tracking, nois appears every few seconds.On AS-3 board replace C041. 0,33uF
no ctl when playingchange R 123 to a 2k7ohms value
drum servo and capstan all over the placeC11 0.47uf is the usual cause, also as already mentioned C41 0.33uf 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.

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