Sharp 37DM23H, 37DT25H, 51DT25H Service Manual

CTV990202

Month of Issue: Febuary 1999

Classification: White

TELEVISION TECHNICAL BULLETIN Page 1 of 1

MODELS 37DM23H 37DT25H 51DT25H

Common faults on the CA1 Chassis

Fault Reason Possible Cause

No teletext Low video input to pin 30 of IC1001 (should be 2.5V). Q201 or Q801

Buzz on sound Noise on audio IF signal or AFT VCO adjustment

incorrect
Erratic start up problems Noise corrupting operation of IC1001/201 See Technical Bulletin CTV981205
Vertical stage problems Various component failures. Note that as the vertical

output stage is DC coupled, a problem at the start of the

stage can have a dramatic effect on the output.
No start up Power supply failure Q702 and/or D718 short circuit
Dead set Power supply running, but no picture and sound – reset

pulse problems
Low HT (40V) Fedback control for the power supply incorrect Check components around the opto-

Note that the CA1\CA10 chassis training course notes are available on the Sharp Electronics (UK) Limited Web Site
(www.tradenet.sharp.co.uk/tech) under the models fitted with these chassis - grouped under the Service Manual
heading. These notes contain in depth details on circuit operation. Please refer to these while fault finding.

If you have a fault to add to the above list, please do no hesitate to contact Sharp Technical Support via the Hot Line
telephone number.

Q801 or poor adjustment of the AFT
VCO

Check all components in the vertical
stage, paying particular attention to
R507/8/22, C510/2/14 and C713

Q704 and/or Q1012

coupler

Sharp Electronics (UK) Limited

Reference AVW150299/1

White – Carry out as required, Yellow – Carry out as required and whenever the unit comes in for service, Red – Carry out on all units

Revision 6