Toshiba 42HL57 No picture No backlight

[neilc6]

Search reveals no posts for this model of TV. When power button is pressed, relay clicks and green LED lights up in front but there is no picture and no backlight.

I found a spanish service manual but the PS board schematic (PE0345) doesn't match what's in the TV (board PE0206)

Inspected PS board - no bulged caps, no burnt components, no cold solder joints, fuses ok

Master and slave inverters - fuse ok and electrolytic caps ok

Power on voltages at PS board connector

12V: 12.3
24V: 0
32V: 31.5
20V: 0

24V to backlight inverters: 0

30V: 0
5V1: 5.1
AC_DET: 3.55
PWR_SIG: 4.91
POWER: 4.61
PROTECT: 2.65 ***
PROTECT: 0

The PROTECT 2.65V line goes to a pin labelled POW_PRO on the Low B board. I've enclosed the schematic for the protect circuit from the service manual. Again, board doesn't match (PE0348 vs PE0347) but guessing it should be close.

From the main board to low B
GND: 0
5V2: 5.2
POWER_PRO: 2.6
POWER_SIG: 4.9 (input to protect circuit)
POWER_LCD: 3.2
AC_DET: 3.5
POWER_DB: 5.0
POWER_TV: 4.7
9V: 9.0

[budm]

Re: Toshiba 42HL57 No picture No backlight

Power_Sig is the same as PS-ON and in your case it is working, if there is PROTEST ERROR (goes high) at 2-B7/5-A2 to turn on the latch Qe100/Qe101 then Qe102 will be on which will take Power_sig (PS-ON) to GDN through that Re107 100 Ohms and that cause the main power supply not to come on, at the same time Qe103 will also be ON so the POWER_PROTECT will also be low. In your case the your POWER_SIGNAL and POWER_PROTECT are high so that means PROTECT ERROR signal is not present and you also show as 0V.
We need good closed straight shot of the power supply board and the inverter board, and bottom side of the power supply board.
Is this where you get the service manual?
http://elektrotanya.com/?q=showresul...oria=&kat2=all


http://www.shopjimmy.com/toshiba-pe0...wer-supply.htm
Toshiba PE0206B Power Supply
Picture provided by shopjimmy.

[budm]

Re: Toshiba 42HL57 No picture No backlight

BTW, do you hear the relay on the power supply board come on?
How about the two white power resistors next to the relay, are they OK?
Right now we need to find out why you do not have the 24V for the inverter board.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

Looks like one of the elektrotanya links (Toshiba 42HL57 SM - zip) has the correct service manual but the dwf files are barely unreadable. The rest of the links are for the portugese (though it was Spanish) Brazilian model with different boards. The service manual is HTML and all the dwf files have red circles on all the components and red lines spreading out from the upper left corner. Tried an online viewer and a dwf conversion program but they all have this problem. Aargh...

The power resistors beside the relays measure R830 - 2.0 ohm and R831 4.9 ohm in-circuit. They match the values in the component list which I was able to view digging into the html files.

R830 76120001 RESISTOR, CERAMIC COVERED, 2.1W 1.8 OHM K
R831 76120003 RESISTOR, CERAMIC COVERED, 5W 4.7 OHM J

On pushing the power button, I hear the relay click once and can turn off as well.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

A was able to make the DWG schematics more readable using a PDF conversion program so that the red lines come out much thinner.

PFC OUT measures 367V so that is ok.

STR-W6765 outputs 32V, 12V and 20V but the components for the 20V line are all marked open so it is probably not used. I am getting 32V and 12V.

STR-Z4579 outputs 30V and 24V which both are reading zero. Likely suspect?

These regulators are common components in Toshiba power supply repair kits. Guess I'll order a STR-Z4579 from China on ebay and wait a couple of months to get here.

Edit: Enclosed a PDF conversion of the power supply schematic for PE0206

[dskall]

Re: Toshiba 42HL57 No picture No backlight

PFC seems on the low side. What is voltage printed on main cap?

[budm]

Re: Toshiba 42HL57 No picture No backlight

The PFC is kind of low.
STR-Z4579: see if it is getting VCC for it to run.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

Re-measured PFC voltage since it is a little tricky getting probes across the ceramic disc cap C822 under a heatsink. 371V this time. Schematic shows PFC output voltage as DC370V. Caps are rated to 450V. Measured across pin 8 (Vcc) to Pin 3 (Gnd) on STR-Z4579 and got the expected 22V. Still haven't ordered it (about $10 USD) shipped from HK or China. Seller ships epacket so it may come quicker.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

The replacement STR-Z4579 arrived today, I put it in, but still not getting 24V nor 30V out.

Can't find a datasheet. Carefully probing, I get the PFC voltage of 370VDC at the input, VCC is 22V and output is 0 which feeds into a transformer. The 24V output of the transformer turns on an optoisolator which connects two pin of the regulator IC.

Next steps are probably to pull the output caps and check them in my esr meter.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

I checked every diode and resistor and pulled off and tested every capacitor in the regulator circuit and didn't find a bad component.

I suspected that the circuit was shutting down into protection mode so I disconnected the 24V connectors for the backlight and checked voltages and found that the 24V for the backlight and 30V were now present. The circuit and regulator are not the fault.

Need to further investigate further down the line. Electrolytic caps on the inverter boards look ok.

Could burnt out ccfl bulbs cause a shutdown??

[dskall]

Re: Toshiba 42HL57 No picture No backlight

Sure bad ccfl's can cause shutdown. I am still suspicious of 370v and would check feedback resistors to your pfc controller for low resistance

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

So I disconnected the pink wires to the backlights and the voltages still shut down so probably not the bulbs.

I removed and tested the samwa caps and they were all ok. Surface mount fuse was ok as well.

Next I checked the four transistors on both boards. The slave transistors seemed ok but was getting shorts on the master board transistors.

Can't find a datasheet on this part. Looks like Fairchild DH15A6. Edit correction: parts are Fairchild FDD8447L

Edit add: Confirmed the short on the master board checking the resistance 24V to gnd.

[budm]

Re: Toshiba 42HL57 No picture No backlight

FDD8447L.
https://cdn.badcaps-static.com/pdfs/...76ac2c733d.pdf
The IC on the Inverter board has no sign of damage? And none of fuses are blown?

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

The IC's show no sign of damage and fuse is not blown. The fuse rating is market 12A so I guess the regulator shuts down well before it gets to that point.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

Ordered the part from digikey but just did a search on ebay and found inverter repair kits with 4 FETs bundled with a BD9897FS IC. If it still doesn't work after replacing the FETs, I guess I will need this IC as well.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

Replace two shorted FETs and they shorted again once I plugged the board back in. Looks like I need to order the controller IC as well.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

Replacement IC came today (8 days epacket from China) and still no go. TV is looking like a lost cause. The FETs are stable now (replaced 3 out of the 4) and so is the 24V and 30V line. There is a blue LED on the board that does a slow flash on when the TV is powered up but still no backlight. Will recheck my soldering on the IC pins and maybe replace the one remaining FET. If it has bad bulbs, then even a replacement board probably won't help though they are pricey on ebay.

[dskall]

Re: Toshiba 42HL57 No picture No backlight

You now have your 24v and turn on signal to inverters?

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

Voltages to the board are stable. I may have had bad soldering on the replacement IC so have reordered it. Replacement inverter boards for this model are fairly expensive but found an Aliexpress listing indicating the following parts are all the same

6632L-0450A / 6632L-0451A
6632L-0371 / 6632L-0372
6632L-0448A / 6632L-0449A
6632L-0474A / 6632L-0475A
6632L-0470A / 6632L-0471A
6632L-0465B / 6632L-0466B

Can anyone confirm? Since some versions of this board are much cheaper, I may try a different pair as well. This TV has the 0450A/0451A pair.

[neilc6]

Re: Toshiba 42HL57 No picture No backlight

Took one last shot and ordered a 474A/475A pair from an ebay seller for $13USD. In contrast, a 450A/450B set was $65.

Checked for shorts before popping them in and now have backlights. Guess my soldering wasn't great when I first replaced the IC. Slight bad news, there are five equally spaced dark spots on the top edge of the screen.