Toshiba 40FT1U

[nubleet]

Looking for a service manual/schematic for the above listed TV. The standby light does not come on. I have checked the supply, and found that I do not get 24v or 12V. However the Rectifier is outputting ~160V. I DO get 5Vcc. Seems I get the correct volt reading on the mosfets. Not sure where to check next.

The power supply board is labelled as a PK101V1760I(2?). Also, FSP188-4f11. The board appears in good shape. The caps aren't bulging, so no easy solution there. Any help is appreciated!

[budm]

Re: Toshiba 40FT1U

For us to help we will need good clear pictures of the whole backside of the TV showing all the boards, and the straight shot pictures of the whole top and bottom side of the power supply board so we can read the printed texts on the board.
It is hard to do long distant troubleshooting without seeing what we are dealing with.
What is the history of the TV? Any works were done to the TV before?
The more details we get the better chance of finding the cause of the problem.

[R_J]

Re: Toshiba 40FT1U

Check the other pins on P802, you should have 3.3v on pin 13 when the power button is pressed, if not you could have a main board issue. Also check pin 14 (ac_det) it should be low around 0 volts

[nubleet]

Re: Toshiba 40FT1U

I have attached pictures of all boards. The set has basically been a PC monitor that has been on since purchase in 2010. It was used as a server monitoring station, running chrome on an auto-refreshing page showing the status of various servers. I came in last Monday, and the set had a standby light on but had no display. I pressed the power button and nothing happened, then I unplugged the set and plugged it back in, and the standby never came back. There has not been any attempt to repair this set outside of my tinkering, which includes disassembly and probing.

I checked P802. I get 92.1mV on ACD, and I get 0.8 Volts on pin13 (PWR) whether the power button is pressed or not. Thanks for the replies!

Update: Checked the VRM on the main board and I get both 3.3v and 5v.

[R_J]

Re: Toshiba 40FT1U

If the power supply is giving a good standby, the main should output a power on voltage back to the power supply.
I see an eeprom U17 on the main board between the lvds cable & crystal, if you have freeze spray or use inverted canned air, try this:
Unplug the tv, freeze the ic, plug in the tv and press the power button.
This sometimes will work to turn the tv on, indicating a fault with the eeprom ic.

[nubleet]

Re: Toshiba 40FT1U

I'll grab some canned air and give this a shot. Thanks for the pointer!

[nubleet]

Re: Toshiba 40FT1U

If the power supply is giving a good standby, the main should output a power on voltage back to the power supply.
I see an eeprom U17 on the main board between the lvds cable & crystal, if you have freeze spray or use inverted canned air, try this:
Unplug the tv, freeze the ic, plug in the tv and press the power button.
This sometimes will work to turn the tv on, indicating a fault with the eeprom ic.

Unfortunately, this did not alleviate the problem.

[nubleet]

Re: Toshiba 40FT1U

Since it appears that I am getting all the voltages that I need (assuming I don't need 12vcc or 24vcc until I get a power on signal from the mainboard) should I bother replacing the Q101 and Q102 (the n-channel mosfets)? It seems like the eeprom COULD still be the problem? If it is, I am assuming that I would need a pre-programmed IC, or just buy a mainboard. Don't want to dump $80+ into a board that is probably not the problem. Any other hints?

[R_J]

Re: Toshiba 40FT1U

Disconnect the cable on P802, then take between a 500Ω and 1k resistor and connect it between 5v standby and PWR pin,that should turn on the power supply. and give you the 12 & 24 volts
or check the value of R234, if it is about 1k then just connect the 5v standby to PWR pin

[nubleet]

Re: Toshiba 40FT1U

an update! Bridging 5v and pwr did indeed get the 12v and 24v readings. I have ordered a pre-programmed ic to replace u17. If that doesn't do the trick, any other places of interest I should investigate?

[nubleet]

Re: Toshiba 40FT1U

I replaced u17, and the issue still persists

[dick_barton]

Re: Toshiba 40FT1U

What's the resistance of the PWR pin to Gnd pin at the main board with the power supply disconnected from it.

Can't really see the tracks to clearly from the photo but does the PWR pin connect back on the main board via resistor R234 and jumper J204 to Q203 which in turn is connected to the opto-isolator PC502?

[nubleet]

Re: Toshiba 40FT1U

What's the resistance of the PWR pin to Gnd pin at the main board with the power supply disconnected from it.

Can't really see the tracks to clearly from the photo but does the PWR pin connect back on the main board via resistor R234 and jumper J204 to Q203 which in turn is connected to the opto-isolator PC502?

4.95kv is resistance from gnd to pwn on main board

That is indeed the path. I've attached an isolated image of that area.

[dick_barton]

Re: Toshiba 40FT1U

It would be 4.95K ohms not K volts.
Can you measure the dc voltage on the 3 pins of the transistor Q203 and at pins 1 & 2 of the opto PC502 at switch on and when bringing it out of standby

[budm]

Re: Toshiba 40FT1U

I thought the power supply is OK since OP can force it on using the resistor between standby and PWR pin and able to get the switched 12V and the switched 24V to come on.
" I get 92.1mV on ACD" This one I am not sure if it is LOW = normal or not. I need to fund my notes.

[nubleet]

Re: Toshiba 40FT1U

It would be 4.95K ohms not K volts.
Can you measure the dc voltage on the 3 pins of the transistor Q203 and at pins 1 & 2 of the opto PC502 at switch on and when bringing it out of standby

My bad... I just got excited :-D

For transistor Q203 top pin, I get 5V, left pin is .2mV, right pin is -.2mV

For PC502, 5V on both pins.

[dick_barton]

Re: Toshiba 40FT1U

I thought the power supply is OK since OP can force it on using the resistor between standby and PWR pin and able to get the switched 12V and the switched 24V to come on.
" I get 92.1mV on ACD" This one I am not sure if it is LOW = normal or not. I need to fund my notes.

Yes indeed the power supply does appear to be fine. Was trying to trace back the PWR signal on the mainboard to see if perhaps a switching transistor or opto has failed. Unfortunately without the schematic it's hard work.

[nubleet]

Re: Toshiba 40FT1U

I'm wondering if maybe the replacement u17 eeprom is working as expected? Nothing changed when I swapped it out. Voltages are all the same still. If you're wondering this is what I replaced with.

[dick_barton]

Re: Toshiba 40FT1U

It appears to be a suitable replacement.

[nelson6861]

Re: Toshiba 40FT1U

what was the end result?