Sansui 9" TV/VCR combo problem with brightness
 

Hi all,

I did a little searching of the group and have read the posts and
replies for a couple of similar situations. I Would like to add some
notes of my conditions before I make my next move.

UNIT: Sansui COM 0952 (Funai, Symphonic variant)

Initial Problem: Power light comes on, but no startup.

Troubleshooting: Replaced 2200uF 105deg electtrolytic on 11.3V supply.

Result: TV powers on with video and sound, however, during startup, the
CRT goes from black to White (is the correct term "full brightness?"
then "fades down" into picture. Picture is nice and clear, colors are
good, contrast is actually really good. Basically, it seems to me that
the CRT is OK.

This set has a 125V B+ line which I think is created via the flyback
from the 11.3V supply. Anyway I monitored the B+ line and it is about
122V during startup. As the CRT comes into its "full white" stage, the
B+ climbs to about 123.2V. Now as the CRT "fades down" down into the
picture the B+ is simultaneously rising to the 125V.

I Checked the electrolytics and rectifiers for the FB scan derived and
power supply circuits and everything seems ok.

When I adjust the Screen (brightness) Pot on the flyback I get a full
raster like i should however when I turn it all the way down I cannot
"dim out" the picture on the CRT. It just gets a "milky-white look to
it". The focus works fine.

I suspect the flyback may be bad (or more correctly-weak?). Perhaps the
internal resistor network is failing or the HV diodes in the multiplier
may be leaky. Anyone had a similar problem with these that turned out
to be the flyback? The reason why I asked is that I repaired another
sansui combo with the same problem, same bad capacitor and now the same
acting CRT startup situation.

It looks like a trend and because there is no separate B+ supply (I
assume because of the AC/DC operation). I suppose it could be a scan
derived supply pulling the B+ down, but I doubt it because of the
unusal Screen control operation and the fact that the Flyback is having
to help generate its own B+(It think...). (Excuse me if I am wrong
here) A guess would be that as the flyback weakens it ceates a huge
startup load for the 11.3V supply which eventually fails the
Electrolytic?

Any help would be appreciated.

John Z.