gEDA-user: Any TV repair gurus lurking?

[Peter Clifton <pcjc2@xxxxxxxxx>]

Hi,

I'm fixing (or trying to) a TV for a friend, and wondered if anyone had
any wisdom relating to the following symptom.

This is a Sony BE-3D chassis, and exhibits an intermittent fault. When
its doing it, the picture is still visible, but collapsed (jitteringly)
upwards towards the top of the screen. It doesn't stay collapsed for
particularly long. The sections of image which collapsed upwards also
narrowed horizontally, leading to a tapered looking screen
---------------
|\           /|
| \         / |
|  \_______/  |
|             |
---------------

(Although this diagram probably exaggerates it somewhat).

None of the obvious supply caps tested for bad ESR on my meter (main PSU
cap, the various secondary side PSU caps including B+, the flyback
derived 200V supply etc.) Even when raster / scan has been lost
completely, sound works fine. At one extreme I saw in person today, the
vertical collapse left three horizontal lines (R,G,B) separated by an
inch or so on the screen towards the top. No picture was visible (and I
turned it off).

I know this set has a common fault with flyback transformers failing due
to internal arcing. I almost convinced myself this was probably the
case, but now I'm not so sure. Could it cause the symptom? (It usually
supposed to trip the sets overcurrent protect on the B+ line and shut
down H drive, throwing the set into standby though - which it didn't
seem to do for me today).

Unfortunately its been several years since I last fixed a TV, and I
don't have my handy box of bits for insulated prodding / light-bulb
inserting / freezing / HV testing. I don't even have an oscilloscope
here (although I could borrow one from the lab). I'm working with
multimeter and ESR meter. I do have the schematics and service manual
though, which is a big plus.

Best wishes,

-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)



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