Toshiba TV model 27A44, Regulated B+ Info
 

Hi,

Note: Now I have the SM.

I fixed a lot of TVs over the years that had excessive HV, but this
Toshiba is out of the ordinary. All the parts that would normally cause
excessive HV in the horizontal sweep circuits tested fine. I removed parts
from the circuit to test. The flyback pulse width on the scope was normal,
within 11 to 14 usec at 10% from base. Note: Other FBT voltages were higher
than normal. The SM, "Basic Adjustments", states the regulated B+ should be
"+123 +/- .5V". This voltage, "+123V" or the HV, can not be found in any
schematic in this SM.

The filter capacitor in the regulated B+ was tested. Due to the time
already spent trying to repair this "DOG", I decided upon a couple
modifications to save this TV from going to the dump. I installed a 5 ohm,
5 watt resistor in the B+ line to the FBT. I also added a .0012uf 2KV
sweep cap across C412 .0027 1.25KV. Now the HV is around 27KV, which I
checked several times during a long run, and the TV has a good picture.

Brad

On Wed, 03 Dec 2008 14:56:54 GMT, Brad wrote:

Hi,

I have a Toshiba TV (27" pic) model 27A44 (mfg. 05/04) in my TV service
shop (no SM). Customer told me the TV "sparks" once in awhile, then turns
off. It didn't do it in the shop yet, but checking the HV, it was 30KV
(higher than normal). I checked the regulated B+ and it measured +122V!
Unfortunately, there is no marking on PCB that indicates what this voltage
should be.

I removed and tested the timing capacitors in the horizontal output
circuit. Sometimes an open capacitor will cause the HV to go higher
than normal. They tested just fine.

130V is very common in my experience, but can someone tell me what the
regulated B+ should be in this model TV?

Thanks in advance, Brad

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