Sony CRT TV Model KV-M1420U thermal problem

My Sony CRT TV Model KV-M1420U has developed a problem. After 15 minutes of perfect picture, the picture fades out by going through a colour change to purple then totally black. All channels are affected. Switching off for a few minutes recovers the picture but the situation repeats.

Anyone one got an idea where I should start to look for this thermal problem? I am trained and familiar with working with high voltage and electronic circuits but I'm not a T.V. engineer.

Beemer

Reply to
Beemer
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Perhaps the CRT filament voltage dies off?

Mark Z.

Reply to
Mark D. Zacharias

| > Anyone one got an idea where I should start to look for this thermal | > problem? I am trained and familiar with working with high voltage and | > electronic circuits but I'm not a T.V. engineer. | >

| > Beemer | >

| >

| | Perhaps the CRT filament voltage dies off? | | Mark Z. | | | Mark,

Only guessing but is there a heater for each primary or is a common heater normally used?

Would the heater voltage be around 12V?

Beemer

Reply to
Beemer

this sounds like a dry joint - probably in the heater line- first check the little board attached to the CRT. Sonys especially tend to develop lots of dry joints, so you'd be well advised to take out the main board and inspect underneath, resoldering anything suspicious. You may even avoid expensive problems ocurring if you're careful.

-B

Reply to
b

If it is a dry joint I assume that it is expansion which results in the failure. Would using a cold spray be appropriate to try to isolate the failing component? I would normally only use a spray on on an semiconductor.

Beemer

Reply to
Beemer

I've used it on joints but on low voltage applications. The thaw could cause moisture to condense and that could adversely affect a circuit with moderate to high voltages.

Reply to
Meat Plow

Beemer ha escrito:

just look for cracked solder on the crt board and near the line transformer (the big 'un).

-B

Reply to
b

best way to find bad joints IME is to tap gently with an insulating rod.

NT

Reply to
meow2222

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