Sanyo Degaussing Circuit Problem
 

Working with a Sanyo DS-27530 27" CRT TV, late 90s vintage. Crazy degaussing circuit is giving me headaches! Problem: popped fuse, keeps popping fuses until the degaussing coils are unplugged. I've seen this problem before with a bad thermistor, so I changed it. Same problem.

Bypassed the fuse with an ammeter and have tried three different thermistors off of different boards (two and three leg which this board has provision for both) and at power up the degaussing coils stay energized until one of the main power resistors begins to smoke. Thermistor jumps from about 20 ohms cold to 150 ohms hot. Is there something I'm missing here?

Some newer sets have a DGS relay. If stuck it will blow
fuse. The 3 legged thermistors gave trouble in Toshibas but
arced. Also 150 ohm hot is very low unless it uses a relay.
BTW sets with a DGS relay may only have one relay. The PS
is always on & on/off is done by turning on/off the hoz osc.
A quick pulse from the micro works the DGS relay.
When running right & warmed up the set should draw apx 3/4 amps.

73 Zeno:smoke:
LFOD !

Thanks! This chassis only has one relay and is definitely a no frills design. All of the PTC thermistors I have on hand top out at about 150 ohms each, so it looks lie they're all for designs incorporating degaussing relays. I even have a NOS replacement degaussing thermistor for a mid 60s color tv and even it tops off at the same 150 ohms. Can you recommend a suitable replacement p/n?

IIRC the common Zenith one for many years was 63-10710.
RCA also used a very common one in the 90's. Dont remember
the 6 digit OEM PN#. Either should work fine IMHO. MOST from a
modern set should be OK.
BTW once in a while sets fuse blew for no real reason. It was the
high current of the DGS causing it. On Toshiba we were told to up
the fuse from 3A to 4A. You can also change to same rating slow-blow.
Also watch out for fuses with Z shaped elements. A lot of crap Korean
ones were being sold back then.

73 Zeno:smoke:
LFOD !

Ok, so changing the degaussing coil on the CRT alleviated the problem. Figure that out! Furthermore, the oil coil measured 10 ohms while the replacement measured about 6, but it works fine without cooking both the thermistor and 5w power resistor. Plugged the old one back in to confirm fix and it started toasting again. I'm aghast.

Must have been shorted turn. Only saw one short in 40 yrs
and that was a tube set. You would never think of it. An example
of tens of thousands of TV's fixed and a simple thing is a dog
to find due to too much experience:scratch2:

73 Zeno
LFOD !