Model: CTM511/5S, CTM631/5S, CTM711/5S -Stereo Televisions
Symptom: The instability of the Stereo Identification Signal on some high quality live stereo
TV programs will cause split-second Sound distortion that may be confused as
‘Sibilance’. Replacement of C015 will improve filtering of the ID signal and remove
any interference causing the effect. Stereo LED indicators may or may not switch
off when distortion is audible. However, re-transmitted programs from
overseas, movies and alike will not show any symptoms.
Instruction: Incoming RF signal must be clean, high quality live transmission to verify if a TV is
effected (use the NEWS or ABC Kids programs for example).
Check Stereo ID signal (˜117.5Hz) present on [TP001] Pin 5 of TDA 3803A (IC001).
The sinewave found should be at least 7.0 Vpp (AC) and may vary slightly in
amplitude from station to station. Instability of this wave is synchronised with speech
and music and will show as a milli-second collapse.
Carefully remove Stereo PCB, disconnection all connectors and the link to the main
PCB (going to R633). Replace C015 from the original 10nF with a 1nF Capacitor .
Reconnect all connectors and the link, check [TP001] again.
[TP001] must be peaked to its
maximum amplitude with
T001 and thereafter readjusted
to a more stable waveform
with a shoulder distortion, as
shown typically 6.5Vpp and
8.5ms , (use a suitable
adjustment tool and
do not readjust any other
potentiometers on the Stereo
PCB).
Please note that the correct adjustment of T001 must result in a distinctive ‘shoulder
distortion’ on the positive rising edge of the sinewave, the falling side is undistorted. This is
not the maximum amplitude adjustment as outlined in the service manual!
Should you require any more information, please fax your enquiry on (03) 646 5554 to the
attention of the Technical Manager.
Zoltan Sekula
Technical Manager
TEAC AUSTRALIA
TECH MEMO #TV#
05.08.94
Distortion on
rising shoulder.
