Toshiba 32WLT66S - No power (completely dead)

[tom66]

Bought this one yesterday - no power, completely dead.

Initially TV came with no fuse in the plug (didn't notice this when buying), however upon putting a good fuse in the plug it's still dead. No standby light, no sign of power.

If I listen carefully, I can hear a faint buzzing, which suggests something is working - maybe a standby output - but that's it.

TV has some Chemicons, Nichicons and Jamicons (ugh). There are a few Jamicons on PSU outputs - bad idea IMO. No bulging caps though, haven't checked for ESR yet.

I've serviced a 42WLT66 before, but this chassis is entirely different. I can't tell for sure but it looks like an LG Philips panel.

Looks like there's no active PFC front end. Instead of active PFC, Toshiba use two big chokes and a large filter cap (470uF.) Surprising that it turns out to be cheaper to do that! PFC is a silly idea really - reduces efficiency (costs more) and only good for the power company.

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Okay, diagnosis...

The standby supply seems to work, it gives 18V and 40V. It seems that Toshiba combined the standby and main supplies, and have a separate supply for 24V for the inverter. Odd design choice.

18V then goes onto the aux power supply board. The only output voltages are 5V and 5.22V, those are two separate 5V supplies. There is an 18V switched line, but it is at about 1V. So, either it's not being switched on (main board issue) or it has failed and doesn't switch on properly given a command to do so (aux PSU issue.) Problem is, the driver PFET is on the bottom of the board so I'm going to have to figure out a way to probe the gate pin.

[selldoor]

Re: Toshiba 32WLT66S - No power (completely dead)

Hi Tom - nothing useful -just a question - in Pic 2 bottom right corner there is a DEC? relay. I had not seen one until recently - there is a post about a set struck by lightning that has one and I tried to find out what it was for and what would happen if it didnt work., but havent found anything much.- Do you know?

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Here's how I probed the gate pin.

I found the gate to be high 18V so the PFET is correctly functioning - it is turned off.

My next place to check is the main board. I've located the microcontroller which manages all the basic functions of the TV, such as switching inputs, power control and fault conditions.

The crystal for the micro is fine but the RESET line (active low, pull low to reset) is at 0V. This leads me to the reset controller potentially being at fault.

I checked the spec for the microcontroller (a Toshiba part): https://cdn.badcaps-static.com/pdfs/...24becde9a4.pdf

Page 31 indicates that RESET requires a clock to work - this explains the unusual behaviour of having a clock while in reset as most microcontrollers don't run the oscillator in reset.

The only way RESET could be low is if the reset controller is stuck shorted, so I'll remove it and then place the bridge RA03.

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Hi Tom - nothing useful -just a question - in Pic 2 bottom right corner there is a DEC? relay. I had not seen one until recently - there is a post about a set struck by lightning that has one and I tried to find out what it was for and what would happen if it didnt work., but havent found anything much.- Do you know?

That relay is the "inrush" relay - its job is to turn the power on to the rest of the power supply. If you connect a 470uF cap straight to the mains you run the risk of tripping the main breaker, so the cap is initially connected in series with some resistors to charge it up slowly. When the TV needs to power up, the relay is engaged, shorting (bypassing) the resistors. The relay will click on when the TV is turned on out of standby. On the 42WLT66 I had, it clicked on in standby and then off again - I guess it was doing some kind of 24V self test when plugged in.

[budm]

Re: Toshiba 32WLT66S - No power (completely dead)

Hi Tom, I just down load the diagram from ELECTROTANYA, the 18/40v sub power supply should be always ON, the 24 power supply is control by the relay and it does not have any softstart (to do softstart, you will will need relay or switch to cut off the power to the current limiter resistor, otherwise the current will keep on flowing through the resistor the minute the TV is plug in).

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Thanks Bud, I found those schematics. The 18V is fine at 18.6V. 40V reads high 48V, but it is only used to generate the 33V for the tuner, there is a simple transistor regulator, so it might only regulate better when the rest of the PSU is under load.

Right now I've found that the RESET line is actually high, was testing it wrong... So I think that bit is fine.

I've found that the microcontroller is telling the POWER_TV to come on, this generates the second 5V rail. However, that's where it stops - no more signals are sent. So, I think it is detecting a fault of some kind. It would be nice if it flashed an LED or something, but it doesn't.

There is a signal AC_DETECT which is low - I think this should be high. I'll see if the microcontroller is looking for this, it might be why it's not powering on.

[budm]

Re: Toshiba 32WLT66S - No power (completely dead)

From what I see in the diagram, instead of using 5vstby to run the processor when unit is in standby, it uses 18vstby instead and it is stepped down to tun the processor, when the it get ON command, it turns on the 24vdc for backlights and xxxV for the audio circuits power supply via relay.
The 18vDC is fed into QE64 which as you said, it should generate the Hi SIGNAL as soon as the TV is plugged in the outlet if the 18v power supply is OK.
I am surprised that it does not have flashing error codes also. Keep us posted. I only worked on a few Toshiba TV, not enough to get indepth how it really works in details.

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

So, I found the POWER_PROTECT line at 2.8V, I think it should be 5V. (Simulated circuit in LTspice, without over-voltage it is 5V.) I lifted the base leg of Q858, still 2.8V. Traced the circuit, it goes through a 10k into base of transistor, so that might be why it is low. No luck getting it working.

Next check is I2C... I'll check if there is any bus activity... maybe there's a corrupt EEPROM somewhere.

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Nothing on I2C... the lines are both continuously high.

This is very strange, it is like something really basic is not being met, it is failing at the first hurdle. I don't want to buy a main board if it's not the issue, but I may have to take a chance. I still don't know for sure if the screen is okay.

Thanks Bud for your input - looks like PSU has these little modules for generating the different supply voltages. The processor is getting good 5Vstby. The reset pin reads 4.85V, I originally suspected maybe it was a square wave (and thus causing the resets) but it is DC.

I've had no luck getting an actual service manual, only schematics - wish there was a troubleshooting flowchart or something similar.

[multimeter]

Re: Toshiba 32WLT66S - No power (completely dead)

http://www.nodevice.com/manual/newma.../get31775.html

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Subscription only scam. They probably don't even have the manual.

There is SM for 32WLG66: http://elektrotanya.com/toshiba_32wl.../download.html

Might be similar enough to use...

[budm]

Re: Toshiba 32WLT66S - No power (completely dead)

I think you mean Q856 (Power Protect generator) with 10k Collector pull-up resistor, the 2.8V is about right (I think you forget to put the load in the LTSPICE) since the load is 10K + Vbe of QA73. The PROTECT signal is generated by QE71 circuits if the 24v dc is working.

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Yeah, that's what I'm referring to. The schematic doesn't have any "expected" values. I'm hoping that maybe the 32WLG66 service manual does but I need to fuss around with Toshiba's silly Zeus engine... Too late and tired to do that, will look at it later, in the mean time I will soon have a nice 24" 1080p monitor to get to work on.

I may simply end up reselling it as I think it will need a replacement main board. That's £18 I suppose not too much but it's only 720p and 32", I usually don't spend too much on trying to get the smaller screens working. Someone more in the know with Toshiba TVs may be better than me. I don't want it to go to landfill though as it seems like it is just a simple problem.

[multimeter]

Re: Toshiba 32WLT66S - No power (completely dead)

seems like a main board issue as you suggested,i see you checked the crystal ,was it outputting the sine wave going into the cpu?,looking up the datasheet for the cpu and seeing if its outputting the signal from the right pin to the psu(possibly ac_det) to turn everything on,also can you drive high the inverter to see at least if your screen is ok?be a shame to get the main board and the screen is buggerd,i hate that when it happens

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Bud I'm looking at that schematic again and it looks slightly different to mine... for example mine uses a 7809 to power audio (and an NPN pass to regulate +26.5V), the schematic shows a 12.4V switcher...

Are the 32WLT66 and 32WLT66S different? I've looked at pics of the main board and that is slightly different - instead of a class D amp they use a class AB with a big heatsink. I think the "S" indicates a cost optimised / "supermarket" version maybe.

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

seems like a main board issue as you suggested,i see you checked the crystal ,was it outputting the sine wave going into the cpu?,looking up the datasheet for the cpu and seeing if its outputting the signal from the right pin to the psu(possibly ac_det) to turn everything on,also can you drive high the inverter to see at least if your screen is ok?be a shame to get the main board and the screen is buggerd,i hate that when it happens

Crystals are both good - there is a 32.768kHz one and another frequency, maybe 16 MHz, but it was good and stable.

There are a few signals to generate to get the inverters going (PSON and dim) I might try that later.

[vinceroger69]

Re: Toshiba 32WLT66S - No power (completely dead)

hi tom66 sounds like this sets being a pain for you to diagnose i was looking on ebay for a different item on another toshiba set but came across this it covers your model http://www.ebay.co.uk/itm/TOSHIBA-32...item2566c8c6b1
not sure if its worth checking on your set?

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Good find Vince - I'll check that later. User did report TV would sometimes get stuck in standby and could take a while to come on although I'm not sure if he meant LED off or something else. Thanks.

[tom66]

Re: Toshiba 32WLT66S - No power (completely dead)

Vince, I think you're a genius - the IC is indeed dead at 0.003V out... should be 2.5V out according to schematic. Hmm, will have to investigate why this is. I may end up using an LM317T to generate 2.5V as the IC is tiny.