Toshiba 37AV500A Regza TV good power supply no sound no picture

[jord4231]

Hi Everyone,

I'm working on a Toshiba 37AV500A Regza TV.

The issue:
TV was working picture and sound went out. Green stand by light stayed on, It will respond to the power button being pressed (goes in and out of standby)
The TV will very intermittently work for around 40 mins then stop. This doesn't seem to matter if its hot/cold unplugged for a while etc.


I checked the PSU voltages and everything looked good.
No bulging caps or signs of heat.

24v aud = 24.41v
12v = 11.98v
5v = 5.062
p_o/f = Goes high to 4.015v when the power button is pressed also the 12v and 24v turn on.
ACD = 0.102v (with this removed the tv won't come out stand by) so I'm fairly confident this is ok.
DIM =3.277v
INV = 0.011v


If I disconnect the INV wire from the connector on the main board
connect it to a external 2v power supply the back light comes on. (still no picture or sound)

With this external supply connected if I put the TV in to standby the back light will also shut off so the inverter board seems to be getting an on off signal


I have traced the INV signal on the main board (pin 1) It goes to c971 ( I
removed and checked this cap off the board ESR and value read ok & yes thats some crusty flux near the C971 capacitor sorry! its the cap up the top of the main board near the board connectors)
It then goes through R836 to C997 to a P chan mosfet U809 (tests ok)

When the tv is taken out of stand by the Voltage rises on the C997 (mosfet
side) of R836 goes to 5.049v but on the side connecting to C971 its 0v
This is why I suspected c971. Even When I removed this capacitor nothing changed it was still 0V pin side of the resistor.


If I disconnect the INV wire or the inverter board it’s still 0V so its not like something on the inverter board is pulling it down, the resistor R836
measures ok at 553 ohms

My only other observations so far is that U811 gets warm on the thermal camera it’s a 5v reg. It has 12v on the in and 5v on its output so I believe it to be ok.

U806 may have an issue it has 5v for memory on the input side and (for memory 0.6v) on the out. (I’ll have to check this) I have not worked out what this is for yet, its close to the processor (with the big heat sink on the left hand side of the control board) in the upper region.

So to recap so far I have all my voltage rails,
My backlight turns on if I bring the INV externally up to 2v (but only if I disconnect the INV wire from the main board connector plug)

The TV is responding to the on off standby switch.

Randomly but occasionally the TV will work as normal.

I have tried warming up the main board with no change.

Nothing else is getting hot.

I have checked for shorts but nothing is glaringly obvious.
Any pointers would be fantastic

I have noticed also a computer will not detect the display currently when its powered on (when the tv is working it will) so I'm feeling like maybe one of the voltage regs somewhere on that main board is not working as it should? I can't see any shorts to ground or low resistance on any of the processor board voltage reg outputs)

I hope this all makes sense I've tried to include as much information as I can for the time being

Kind regards and thank you

[dskall]

Re: Toshiba 37AV500A Regza TV good power supply no sound no picture

Are you getting voltage to your t-con? Also to properly heat up processor you would need to remove heat sink. Is optical port lit?

[jord4231]

Re: Toshiba 37AV500A Regza TV good power supply no sound no picture

Thanks for the reply @dskall It was just a general warm up for the board at this stage.
I'm not getting the optical output lighting up.

I will need to get to the tcon board behind this lot to make sure its getting power. Something I have not checked / was not really sure about yet thanks for the tip! I'll report back soon

[jord4231]

Re: Toshiba 37AV500A Regza TV good power supply no sound no picture

Are you getting voltage to your t-con? Also to properly heat up processor you would need to remove heat sink. Is optical port lit?

I've got nothing on any of the pins going to the t-con. Also the optical is definitely not lit. To confirm further to my post u806 only had .5v out on it. Its a ld117al not sure if this is related but its in that region on the board

Thanks again

[nomoresonys]

Re: Toshiba 37AV500A Regza TV good power supply no sound no picture

unplug everything from the powerboard, plug power cord into powerboard, remeasure the pins, report results.

[dskall]

Re: Toshiba 37AV500A Regza TV good power supply no sound no picture

I've got nothing on any of the pins going to the t-con. Also the optical is definitely not lit. To confirm further to my post u806 only had .5v out on it. Its a ld117al not sure if this is related but its in that region on the board

Thanks again

Looks to be a regulator. I think there is a voltage code on it. Need to remove it and check for shorts. What is input voltage?

[jord4231]

Re: Toshiba 37AV500A Regza TV good power supply no sound no picture

Looks to be a regulator. I think there is a voltage code on it. Need to remove it and check for shorts. What is input voltage?

5v in should be 1.8v out I have 0.5v I've removed it don't seem to have any shorts, I'll bench test the reg out of circuit and see what happens

[jord4231]

Re: Toshiba 37AV500A Regza TV good power supply no sound no picture

Solved 1.8v voltage regulator had gone bad. Replaced and up and running!