Sony KDL-40BX450 LCD. Thermistor gets too hot 10 seconds after turning on the TV

[Diah]

Originally Posted by Quantum IC

When I press the power button for the first time after plugging in the TV, the voltages are present for about 1-2 seconds and then drop to 0V, except for the STBY 3.3V and AC OFF DET 3V voltages, which are always present.
Then when I press the power button again the TV turns on and all the voltages are present.

common man.. did you read about Sony firmware it can register failure account.. what the eeprom will do if the sectors space are full...it will try to shutdown then delete the last one and turn on again normal.. log in SM and clear this register.

[nomoresonys]

That sounds right to me Diah, I do believe you are correct sir.

[Quantum IC]

Originally Posted by Diah

common man.. did you read about Sony firmware it can register failure account.. what the eeprom will do if the sectors space are full...it will try to shutdown then delete the last one and turn on again normal.. log in SM and clear this register.

How can I log in SM and clear the register?
I don't have the remote and the owner of the TV lost it.

[gabiz_ro]

That called thermistor is an NTC and is wide used in SMPS as inrush current resistor.
On older designs there was a resistor from bridge rectifier to main capacitor,but since even a little value generate some power loss , they switched to NTC.
When cold have some low ohm value to limit inrush current when connected to main voltage then heat up,resistance decrease to almost 0,no voltage drop across NTC,no power loss

[Quantum IC]

I replaced the thermistor with a 2.2Ω 7W ceramic resistor because I couldn't find a similar thermistor and just as a test to rule out if the thermistor was faulty.
This resistor also gets very hot in about 1 minute.
I can't figure out why, if when I take the amp reading through the thermistor or through the resistor, I don't get a high draw.

[R_J]

Originally Posted by Quantum IC

I replaced the thermistor with a 2.2Ω 7W ceramic resistor because I couldn't find a similar thermistor and just as a test to rule out if the thermistor was faulty.
This resistor also gets very hot in about 1 minute.
I can't figure out why, if when I take the amp reading through the thermistor or through the resistor, I don't get a high draw.

That's because a RESISTOR is not a NThermistor. the resistor never changes to 0Ω it is always 2.2Ω and the voltage drop will case heat. Remove the resistor and replace it with a NTC THERMISTOR

[dskall]

A thermistor will get hot. Look up temp. specs. on it. It will burn your fingers.

[dkneyle]

Originally Posted by Quantum IC

I think you're wrong. Of course, 250W is too much, it's even above the consumption marked on the label of this television.
But I got 600~700mA (0.6~0.7A) and if I'm not mistaken that means around 66~77W.
Mi line voltage is 110V.
The label on this TV says a power consumption of 158 W.
It's an LCD TV. Its backlight is by CCFL lamps.

Apologies - you are right about 110VAC - I calculated wrong.

[dkneyle]

CCFL TV will have an inverter circuit. I'd still be looking closely there for a problem.

[vinceroger69]

Training manual link
https://www.manualslib.com/products/...50-491425.html

[nomoresonys]

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