1992 19" Zenith squealing, strange failure modes
 

1992 Zenith SS6043S 19" remote, made Sept of 1992 just on that border
of bad bad tubes. Set has given 14 years of trouble free operation as
a bedroom set. Problem is that it began squealing so loudly it is
almost deafening. This is not through the speaker, but through some
mechanical oscillation on the board itself. When plugged in yet in
standby mode (off), I can hear a faint squeal like the HOT is trying to
start. Frequency of the squeal varies strangely while in standby.
This leads me to believe it's something in the power supply, or is
there some bleeder voltage applied to the HOT and flyback at this
point? Power-on often results in no HV, but you have audio and tuner
functionality. Unplugging and replugging makes the set "forget" this
mode and give a raster on next poweron. When the HV is running,
picture is great with full raster. Colors are all well balanced, focus
is sharp, no retrace or anything. No signs of the dreaded shorting
picture tube. But the squeal is deafening, increasing on bright
scenes. Turning the sub-brightness of course changes the intensity,
and turning it down completely will start the HOT every time. I
haven't been able to isolate where on the board this is coming from.
Physical stressing of the board and individual parts with an dry wooden
dowel does nothing to help find the oscillating part. There have been
a couple of occasions where changing the channel kills the HV.
Strange, no? Audio and other functions remain, but the CRT goes into
shutdown.

Would this be symptomatic of a failure in the SMPS, the flyback, or a
failing HOT? Not sure where to start, so far flying with no data (I
know I know, get a Sam's).

Thanks!

1992 19" Zenith squealing, strange failure modes
 

Change the two small electrolytics on the primary. 22uf@63volt and
100uf@25volt. On the 22uf, you can use a 50volt rating just fine. The
22 is probably the culprit for the squeal.

www.techdata-kicksass.net

1992 19" Zenith squealing, strange failure modes
 

ha1156w:
Probably high ESR or otherwise faulty electrolytics in the SMPS.... or
possibly elsewhere on the board on the power supply secondary B+ rails or
flyback derived B+ rails..
An ESR meter will help find the faulty electrolytics otherwise the procedure
of bridging or substitution is the way to find them.... with the help of an
oscilloscope..... and an isolation transformer.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
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1992 19" Zenith squealing, strange failure modes
 

Thanks a million -- you were spot on. I replaced those two caps and
the oscillations returned to normal!