Toshiba 19BL502B replaced diode worked, now not working

[budm]

Re: Toshiba 19BL502B replaced diode worked, now not working

Example of the LCD panel spec showing the command signals, one of the reason I always ask for LCD panel number so I can get more details about the panel.

[budm]

Re: Toshiba 19BL502B replaced diode worked, now not working

In standby it is zero on turning on it goes up to 3.09 volts then slowly reduces (over about 10 seconds) to 0.23, have repeated several times.

Thanks David

OK another one of those failed dimming control problem.
Disconnect the Dim control wire going back to the main board and see what happen.

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

OK another one of those failed dimming control problem.
Disconnect the Dim control wire going back to the main board and see what happen.

Have cut wire from PSU to LED Driver board.

Coming from PSU/Main Board
on standby 0.312
Turned On goes to 3.4 and then drops back to 0.257

No voltages on wire from LED Driver board

Thanks David

[budm]

Re: Toshiba 19BL502B replaced diode worked, now not working

Have cut wire from PSU to LED Driver board.

Coming from PSU/Main Board
on standby 0.312
Turned On goes to 3.4 and then drops back to 0.257

No voltages on wire from LED Driver board

Thanks David

So dim command wire is no longer connected back to the main board, right?
So where do you still see this 'Turned On goes to 3.4 and then drops back to 0.257' if the wire going to the main board is not connected?

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

So dim command wire is no longer connected back to the main board, right?
So where do you still see this 'Turned On goes to 3.4 and then drops back to 0.257' if the wire going to the main board is not connected?

That is coming from the main Board via the PSU board.
Because the PSU board is connected via a 20 Pin plug I could not see any way to disconnect the wire there and as the 6 way connector has wires going to the LED driver Board I cut the wire there and measured either way

Look at the PSU schematic the PWM_DIM appears to go straight through to the Main Board.

Is this just so the TV can control the Level of Background light?

Thanks David

[budm]

Re: Toshiba 19BL502B replaced diode worked, now not working

So if you look at the dim line on the LED driver board, it shows 0VDC, correct? if it does, then connect 1K resistor between the dim line on the LED driver board and the STBY power supply to see if the backlights will come on and stay on.

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

So if you look at the dim line on the LED driver board, it shows 0VDC, correct? if it does, then connect 1K resistor between the dim line on the LED driver board and the STBY power supply to see if the backlights will come on and stay on.

Yes that was correct Led Driver board showed 0 dc volts.
Connected a 1K resistor between dim line on the LED driver board and the 5 volt standby but backlights do not come on, reading across 1K resistor 5.04 Main board side and 4.84 volts Led Driver Board side.

Thanks for all your help David

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

Which are the connections to the LED's? the only connection other than the one from PSU is the one circled red which is a small ribbon cable is this the connection the LED's?
How to test the LED's?
Which components are the Boost Converter?

Thanks David

[kc8adu]

Re: Toshiba 19BL502B replaced diode worked, now not working

in the future replace all parallel diodes with the same type.or 1 properly heatsinked high power type.this power supply is a well known bad design.
if you must use multiple diodes use high quality ones from the same lot.
better chance of vf being the same.
i suspect feedback is on +12 and it going low due to bad diode overshot +24 and killed something in the led driver most likely the control ic.

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

in the future replace all parallel diodes with the same type.or 1 properly heatsinked high power type.this power supply is a well known bad design.
if you must use multiple diodes use high quality ones from the same lot.
better chance of vf being the same.
i suspect feedback is on +12 and it going low due to bad diode overshot +24 and killed something in the led driver most likely the control ic.

All three diodes were replaced together from same lot.

Has it damaged Main Board as well because the PWM_DIM signal goes down to 0.23 volts.

David

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

Which are the connections to the LED's? the only connection other than the one from PSU is the one circled red which is a small ribbon cable is this the connection the LED's?
How to test the LED's?
Which components are the Boost Converter?

Thanks David

[dick_barton]

Re: Toshiba 19BL502B replaced diode worked, now not working

What voltages do you have on pin 1 ------> 20 and at the two red arrows when the set is powered up normally.

I suspect the TPS61199 (Led Driver IC) may well be damaged since it has a maximum working voltage of 30V and you said that the 24V supply was initially rising above that.

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

What voltages do you have on pin 1 ------> 20 and at the two red arrows when the set is powered up normally.

I suspect the TPS61199 (Led Driver IC) may well be damaged since it has a maximum working voltage of 30V and you said that the 24V supply was initially rising above that.

At the two red arrows I have zero volts.

On the TS61199 I have Pin1 = 0.17 volts and Pin 20 = 1.27 volts the rest are all zero volts.

Thanks David.

[dick_barton]

Re: Toshiba 19BL502B replaced diode worked, now not working

Were these taken while 24V was being supplied to the LED controller board?

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

Were these taken while 24V was being supplied to the LED controller board?

Yes, well it's shows 27 volts

[dick_barton]

Re: Toshiba 19BL502B replaced diode worked, now not working

If that's the case then you have a faulty led controller board since the TS61199 (Led driver chip) supply pin (pin 18) has no voltage on it to run it.

[vinceroger69]

Re: Toshiba 19BL502B replaced diode worked, now not working

have you re joined the wire you cut when budm was getting you too run tests

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

have you re joined the wire you cut when budm was getting you too run tests

Yes

[David-OLW]

Re: Toshiba 19BL502B replaced diode worked, now not working

If that's the case then you have a faulty led controller board since the TS61199 (Led driver chip) supply pin (pin 18) has no voltage on it to run it.

Replaced Led Driver Board and it worked.
Only lasted for 5 days and backlight not working again.

I think it's time to give up and buy a new TV.

I think it is still connected to do with the power supply as I have 11.5 volts and 27 volts. The 27 is probably putting high volts on Led circuit. Don't know how sort PSU to get 12 volts and 24 volts.

David

[ReeceyBurger123]

Re: Toshiba 19BL502B replaced diode worked, now not working

Sell her to me