Toshiba 50L1350uc no back light

[osheam]

No back light; voltages with TV on are:
L2- 19VDC
L2+ 76.9VDC
L1- 27.4VDC
L1+ 76.9VDC

PWM: .2V
5.1V: 5.1V
BL_On/Off: 3.3V
Power_TV: 3.5V
AC Detect: 3.5V
5.1V: 5.1V
GND: 0V
12V_LNB: 12.4V
GND: 0V
12V_AUD: 12.4V
GND: 0V
GND: 0V
12Vcc: 0V
12Vcc: 12.4V
12Vcc: 12.4V

Pwr board: PK101W00501

Based on what I have read in this forum; I am thinking of replacing the pwr supply board (PK101W00501); is this reasonable?

[budm]

Re: Toshiba 50L1350uc no back light

https://www.badcaps.net/forum/attach...9&d=1485131974
Can we get better pictures?

'L2- 19VDC
L2+ 76.9VDC
L1- 27.4VDC
L1+ 76.9VDC
Are those reading ref to chassis?

[osheam]

Re: Toshiba 50L1350uc no back light

See attached pic; not quite sure what you mean by "reading ref to chassis" but the readings are from the plug that powers the led strips;I grounded to the chassis when measuring the output voltage and there was a surge on L2 when powering on but not so much on L1.

[budm]

Re: Toshiba 50L1350uc no back light

It means using chassis as the GND ref point for the meter.

[budm]

Re: Toshiba 50L1350uc no back light

Disconnect the LED connector, black probe on the chassis, red probe on L1+ then turn on the TV and see how high the Voltage goes up to, then do the same for L2+.

What is the DCV rating of cap C901A/B?

Toshiba 75033153 (PK101W0050I, FSP156-3FS01) Power Supply Unit
http://www.shopjimmy.com/toshiba-750...pply-unit.htm#

Pictures provided by shopjimmy.

[dskall]

Re: Toshiba 50L1350uc no back light

One 12vcc reads 0v

[budm]

Re: Toshiba 50L1350uc no back light

That is probably a reading error since 12VCC pins are tied together.

[osheam]

Re: Toshiba 50L1350uc no back light

Disconnect the LED connector, black probe on the chassis, red probe on L1+ then turn on the TV and see how high the Voltage goes up to, then do the same for L2+.

What is the DCV rating of cap C901A/B?

Toshiba 75033153 (PK101W0050I, FSP156-3FS01) Power Supply Unit
http://www.shopjimmy.com/toshiba-750...pply-unit.htm#

Pictures provided by shopjimmy.

L2 surges to 130vdc and L1 82vdc; C901/901 rated both 250v.

[budm]

Re: Toshiba 50L1350uc no back light

There are two Voltage boost converter circuit, one for LED string L1+, and another one for the L2+, both of them should show the same boosted Voltages, so right now L1+ is not working.
So are you sure that is that you did not see L1+jumps up to 130VDC?

[osheam]

Re: Toshiba 50L1350uc no back light

There are two Voltage boost converter circuit, one for LED string L1+, and another one for the L2+, both of them should show the same boosted Voltages, so right now L1+ is not working.
So are you sure that is that you did not see L1+jumps up to 130VDC?

L2 surges to 133vdc whereas L1 to only 81vdc; does that indicate c901 A or B is not discharging correctly?

[budm]

Re: Toshiba 50L1350uc no back light

Right now we need to inspect the parts in the L1+ Booster circuit section. Check the diodes, the MOSFET, etc.

As you can see if you trace out the board, C901A is filter cap for L2+, C901B is filter cap for L1+.

[osheam]

Re: Toshiba 50L1350uc no back light

Right now we need to inspect the parts in the L1+ Booster circuit section. Check the diodes, the MOSFET, etc.

As you can see if you trace out the board, C901A is filter cap for L2+, C901B is filter cap for L1+.

Thanks Bud for your input; and I will check the diodes but at this point would you say a replacement pwr board "should" fix this tv?

[budm]

Re: Toshiba 50L1350uc no back light

If those readings are correct and no measurement error on your part, then right now that power supply board is bad.
Another problem that I am seeing is the:
PWM: .2V
It should not be that low, you need to check that Voltage on that pin when TV is first turned on to see if it is higher than 2V or so and then drops down to 0.2V or not or it stays at 0.2V when TV is first turned on and no change.

[osheam]

Re: Toshiba 50L1350uc no back light

If those readings are correct and no measurement error on your part, then right now that power supply board is bad.
Another problem that I am seeing is the:
PWM: .2V
It should not be that low, you need to check that Voltage on that pin when TV is first turned on to see if it is higher than 2V or so and then drops down to 0.2V or not or it stays at 0.2V when TV is first turned on and no change.

PWM jumps to 3.2vdc when powering on and then settles to .2vdc.