Toshiba 26AV600A

[Amraks]

Re: Toshiba 26AV600A

Check all the diodes on the powerboard, good place to start and easy enough to do.

checked over the diodes no bad readings from any of them.

Now I’m really stuck.

[nomoresonys]

Re: Toshiba 26AV600A

Maybe try testing powerboard, with cable from CN902 to mainboard UNHOOKED, use about a 1k resistor to jump PS_on to +5v pin and another resistor from ON/OFF to +5v, plug the power into powerboard, see if you get the backlights on and if those voltages come up.

[Amraks]

Re: Toshiba 26AV600A

Tried forcing it on with out the mainboard plugged in none of the voltages I was getting are appearing.

[R_J]

Re: Toshiba 26AV600A

check R925 (0.1Ω) and R930 (0.43Ω), if they are ok, use hot ground to check the voltage on Q970 Drain (should be pfc voltage) if it is ok, check the voltage on C977 (15v)

[Amraks]

Re: Toshiba 26AV600A

check R925 (0.1Ω) and R930 (0.43Ω), if they are ok, use hot ground to check the voltage on Q970 Drain (should be pfc voltage) if it is ok, check the voltage on C977 (15v)

r925
0.2 Ω

r930
0.4 Ω.

[R_J]

Re: Toshiba 26AV600A

The resistors are ok, so the fets are likely ok, Now check the voltages

[Amraks]

Re: Toshiba 26AV600A

So checked

Q970
396v

c977
13.18vdc

C977 is meant to be 15 volts isn't it?

[R_J]

Re: Toshiba 26AV600A

The 13 volts is ok for the ic's vcc, Check the voltage on ic970, pin 7, and pin 5 (look at the schematic and locate a nearby component to check the voltage to avoid shorting the ic pins (IE: pin5 use C991 orR992)
It could be that IC870 is bad.

[Amraks]

Re: Toshiba 26AV600A

done these checks.

Pin 5
2.6mV

Pin 7
1.98V

[R_J]

Re: Toshiba 26AV600A

It would seem the ic is in standby, pin 5 needs to be above 50mv. Check the two resistors, R932 (3.9k) and R992 (100Ω) if they are ok, check that the optocoupler is not bad and that C991 is not shorted

[Amraks]

Re: Toshiba 26AV600A

r932 is good
r992 is good
c991 isn't short
optocoupler isn't shorted.

[Amraks]

Re: Toshiba 26AV600A

optocoupler
2.91v on pin 1 using chassis as ground

2.0Mv on pin 4 using filter cap as ground.

Would it be safe to say this optocoupler is no good?

[R_J]

Re: Toshiba 26AV600A

I don't believe the optocoupler is the problem
The datasheet says that pin 4 provides a 2v reference voltage which should show up on one end of R932, This voltage is from the ic itself so I suspect if it is missing the ic is the problem. If the optocoupler is not shorted, then the 2 volts from pin4 should go through R932, R992 and back to pin5 (the standby pin) and should be around a minimum of 1.3v
It seems the circuit is slightly working and likely stuck in burts mode. otherwise you shoud not have any voltage on the 24v1 supply, this is where pin1 of the optocoupler gets its voltage and is getting 2.91v.

[Amraks]

Re: Toshiba 26AV600A

I don't believe the optocoupler is the problem
The datasheet says that pin 4 provides a 2v reference voltage which should show up on one end of R932, This voltage is from the ic itself so I suspect if it is missing the ic is the problem. If the optocoupler is not shorted, then the 2 volts from pin4 should go through R932, R992 and back to pin5 (the standby pin) and should be around a minimum of 1.3v
It seems the circuit is slightly working and likely stuck in burts mode. otherwise you shoud not have any voltage on the 24v1 supply, this is where pin1 of the optocoupler gets its voltage and is getting 2.91v.

Cheers R_J and everyone else a new chip solved the issue and bought the TV back to life.

This TV bought some different symptoms to the table for when this chip goes bad anyway.

[nomoresonys]

Re: Toshiba 26AV600A

So which one was bad, IC870 or IC970?

[Markus1]

Re: Toshiba 26AV600A

So which one was bad, IC870 or IC970?

I believe his final replacement was IC970.

[nomoresonys]

Re: Toshiba 26AV600A

Thanks Markus.