Toshiba 32L3753DB no power. Replaced PSU.

[willpierce]

I'm having a problem with this Toshiba TV. A friend asked me to take a look at it. She said it suddenly stopped working.

As a replacement Vestel PSU was only £5 on ebay, I bought and fitted, but made no difference.

- There is no standby light
- It does not respond to power button on rear or remote
- The optical port is lit on the rear, but that's the only sign of life.
- I measured a 3.3v and 12v supply on the interconnect between psu and mainboard.

I'm assuming that the PSU is OK, as it is a replacement. But without knowing exactly what to measure for, I'm not 100%

I downloaded the datasheet for the Vestel 17ips62, and measured (I hope I got this right)

pin3 - STBY_ON/OFF - 0v
pin5 - BKL_ON/OFF - 0v
pin7 - PWM_DIM - 3.36v
pin11 - 12V - 12v

I'm assuming the pins on the connector that are accessible are 1-3-5-7-9-11, with 11 (12v) closest to the top of the board.

I don't really know where to go from here. If I knew it was definitely the mainboard, I'd replace it as they're really cheap. Any help would be greatly appreciated.

Thanks,

Will

[nomoresonys]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Simple things first, check all the diodes, check the solder joints on the bottom of board, look closely at solder joints of components on heatsinks and transformers, you should probably measure all of the pins not just odd, maybe use a stripped bread tie to get into tight areas. As always BE VERY CAREFUL when working with powerboard, DEADLY VOLTAGE on HOT side.

[nomoresonys]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Some testing procedure there: https://www.youtube.com/watch?v=ocqnqmBxiqY

[arizanotlari]

Re: Toshiba 32L3753DB no power. Replaced PSU.

hello.

check output of u63.
if 5v missing check chassis for short circuit.
if 5v is normal, check u81.
if 3v3 is normal rewrite u81.

[yokoono]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Vestel motherboards are "renowned" for software issues. Also post the panel code to search for the required software.

[willpierce]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Simple things first, check all the diodes, check the solder joints on the bottom of board, look closely at solder joints of components on heatsinks and transformers, you should probably measure all of the pins not just odd, maybe use a stripped bread tie to get into tight areas. As always BE VERY CAREFUL when working with powerboard, DEADLY VOLTAGE on HOT side.

Hi, thanks for the tips. I have done a good visual inspection and checked all the diodes and caps (except for 2 I couldn't test in-circuit) OK, and the power board is a new replacement, so I'm 95% sure it's OK, just wanted to confirm what the outputs should be. The Vestel schematic gives no voltages.

I can access all the pins ok (I have an IC hook probe thingy), I just gave the ones that were not ground or unused.

I think the problem is elsewhere, probably the mainboard. I just wanted someone to confirm that the outputs I was getting from my PSU were correct before I discounted it completely.
I was thinking that the STBY_ON/OFF and BKL_ON/OFF were supposed to be at zero until turned on by the mainboard? And that the PWM_DIM was correct at 3.3v? Therefore my PSU was fine...

That is about as advanced as I get though, so any other suggestions welcome.

[willpierce]

Re: Toshiba 32L3753DB no power. Replaced PSU.

hello.

check output of u63.
if 5v missing check chassis for short circuit.
if 5v is normal, check u81.
if 3v3 is normal rewrite u81.

Thanks. I am pretty out of my depth when it comes to this sort of thing. I measured all the voltages of the pins, and have attached an updated image. Sorry if it's a bit hard to read.

I checked for shorts to ground, but could not find any, but my experience in this is limited.

What did you mean by "rewrite U81"?

Thanks again

[willpierce]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Vestel motherboards are "renowned" for software issues. Also post the panel code to search for the required software.

I have been reading about this. I never realised so many brands used these same crappy generic parts, just with their own firmware.

The TV seems totally dead apart from power going to the optical port. I tried the factory reset (hold pwr for 1min, plug in, etc...) but nothing.

Can a software glitch cause this issue? I have no light error-code flash or anything like others describe... It is just dead, so there is no way to flash new software I don't think?

Thanks.

[nomoresonys]

Re: Toshiba 32L3753DB no power. Replaced PSU.

"pin3 - STBY_ON/OFF - 0v
pin5 - BKL_ON/OFF - 0v" If both of these are at zero when you hit power on, tv won't work, signals come from mainboard.

[arizanotlari]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Thanks. I am pretty out of my depth when it comes to this sort of thing. I measured all the voltages of the pins, and have attached an updated image. Sorry if it's a bit hard to read.

I checked for shorts to ground, but could not find any, but my experience in this is limited.

What did you mean by "rewrite U81"?

Thanks again

i check photo and i think sda/scl signals not correct.

rewrite meaning is reinstall spi firmware via flash programmer. if you need dump file send me pm.

[willpierce]

Re: Toshiba 32L3753DB no power. Replaced PSU.

"pin3 - - 0v
pin5 - BKL_ON/OFF - 0v" with both of these at zero when you hit power on, tv won't work, signals come from mainboard.

Neither voltage changes from zero when I hit power on.

The original PSU has same zero voltages on these pins too.

I thought it was unusual that they would be zero, but just assumed that they were 'low' until signaled from the mainboard (which does have power running through it).

So this new power supply is faulty also, or is it a mainboard problem? Do you know what voltages these pins should be?

Thanks very much.

[nomoresonys]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Those signals come from the mainboard. I would speculate that maybe both your psu's are good, thinking both pin 3 and 5 should be over 3 volts when working correctly and power on is applied.

[nomoresonys]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Since they're cheap, grab a mainboard, just make sure it's a match.

[willpierce]

Re: Toshiba 32L3753DB no power. Replaced PSU.

i check photo and i think sda/scl signals not correct.

rewrite meaning is reinstall spi firmware via flash programmer. if you need dump file send me pm.

Ah, OK. I understand, thanks very much. I normally fix PC's! It's years since I used an EEPROM programmer, i'd need to order one and set it all up.

A replacement mainboard is £10 on ebay. If it were 100, or even maybe 50 I would definitely try the reflash!

The mainboards are very specific to model/screen ID, so if I struggle to source one for this particular TV, I may take you up on your offer.

You've been very helpful. Thanks.

[willpierce]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Since they're cheap, grab a mainboard, just make sure it's a match.

This is exactly what I'll do. Thanks for all your help, it's much appreciated

[R_J]

Re: Toshiba 32L3753DB no power. Replaced PSU.

Your power supply is likely ok. It is common for the eeprom to be corrupt. if this happens the microprocessor does not know what to do, so when it sees the power buton being pushed, it does'nt know that it should issue a power on command to the power supply etc.
There is a trick that sometimes works using freeze spray (or an inverted canned air duster)
To do this, unplug the tv from the ac, freeze the U81 ic, wait 10~20 sec for the freeze to take, Plug in the tv and try to turn it on. If this works the fault is with the U81 ic.
If it does'nt work it could still be a corrupt U81 ic.