Panasonic Viera TX-L32E3B won't power up, green LED flashing

[lamlash]

Hi,

I am attempting to repair a Panasonic Viera TX-L32E3B, chassis GLP26 for a friend.

There is no sound or picture. When switched on the green LED flashes rapidly about 44 times then goes solid. Pressing any button on the TV or remote causes the green LED to go out. The red LED never comes on.

My friend said that the TV recently started doing this and would sometimes work if powered off and on again. Now it doesn't work at all.

I carefully inspected the power board and there's no obvious damaged components or bad soldered joints. With the board powered up and all connections left plugged in, I measured the following on the two connectors:

P2
1 5.74V
2 5.74V
3 0V
4 15.99V
5 15.99V
6 15.99V
7 0V
8 2.49V
9 5.74V
10 1.3V
11 3.28V
12 3.27V
13 0V
14 0V
15 0V
16 0V

P4
1 0V
2 0V
3 0V
4 3.26V
5 0V
6 0V
7 0V
8 0V
9 0V
10 24.6V
11 24.6V
12 24.6V
13 24.6V
14 24.6V


I found a service manual for this chassis on another badcaps thread and it lists test-point voltages for the power board. With 2.5V on TV_SUB_ON on P2 pin 8, I measured the following voltages on the P Board:

TP7514/TP7515 (24V, PANEL) : MEASURED 0V (should be 24V +/-1.2V)
TP7503/TP7504 (16V) : MEASURED 0V (should be 16.1V / +/- 0.7V)
TP7502/TP7501 (TUNER5V8): MEASURED 0V (should be 5.7V +/- 0.3V)
TP7201/TP7203 (PFC): MEASURED 388V (in spec - should be 400V +/-15V)

Could someone suggest next steps?

Thanks

[nomoresonys]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Heat up the powerboard with a hairdryer be sure and heat the capacitors, then see if tv comes on or changes if not then heat the mainboard same way, see if anything changes. That little test works with certain conditions including raising the esr on a cap that is bad or marginal enough to make the tv work for a very short time.

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Heat up the powerboard with a hairdryer be sure and heat the capacitors, then see if tv comes on or changes if not then heat the mainboard same way, see if anything changes. That little test works with certain conditions including raising the esr on a cap that is bad or marginal enough to make the tv work for a very short time.

Thanks, I'll give that a try tonight (I'm in the UK here). Any follow-up tests you can suggest? Is it worth unplugging the LED driver board from the power board to see if I can get a red standby LED to come on?

[diif]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

It helps if we can see the boards and how they are connected together although looking at your voltages I'd investigate the backlights and circuitry as pin 4/12 is BL_SOS.

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

I've uploaded an image in case that helps

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

It helps if we can see the boards and how they are connected together although looking at your voltages I'd investigate the backlights and circuitry as pin 4/12 is BL_SOS.

My information shows that Pin12 on P2 and Pin4 on P4 are the BL_SOS signals. Mine are at 3.3V so does that mean the LED board is asserting a BL_SOS signal?

[Diah]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

the sickness of Panasonic always the LED back light sockets. they choice such kind with heating get out from it place. start to take screen apart and inspect LED back light.

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

the sickness of Panasonic always the LED back light sockets. they choice such kind with heating get out from it place. start to take screen apart and inspect LED back light.

OK thanks. I stripped the screen apart (lots of screws, lots of pieces!!) and have the LED strips out. This is an edge lit TV with 2 strips of small surface mount LEDs on a thin aluminium PCB. Each strip has 42 LEDs. Have you any advice about testing the LED strips?

The part numbers of the left side LED strip is 010312-L4 / 110616A-0312. The connectors look absolutely fine. Does your advice about the connectors apply to these edge lit LED panels?

Many thanks by the way!

[Diah]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Panasonic can work and LED back light too with out screen in place.. so keep the screen at safe place till you have done .

yes the edge one had this sickness.. the mother socket which soldered at the strip

try to turn it on and keep eyes on the LED if they blink some how

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

OK thanks. I have dismantled too many parts to test the LED strips using the TV power supply. Do you know approximately what the I-V operating point of each LED should be? I could connect each LED to a current limited bench top power supply. Does 3V limited to 10mA seem reasonable to light up each LED without damaging it?

Here's a photo of the connector - I can't see any problem with them.

[diif]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Around 200mA to test the LEDs properly.

[Diah]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

NO, you can use your DM in Diode mode. ( peep ton ) and test each one. the reading will be if - + correct it will light on a little depend on your DM battery. and when you exchange the red and black at opposite place it should read Diod round 0.75ß-0.540. if one not goes on but read correct Diode it mean its OPEN. if one powered on but no Diode reading or it peep mean its shorted. and this most case.

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Thanks.

Each strip has 42 LEDs. The circuit arrangement is 3 parallel sets of 14 series-connected LEDs.

When you say 200mA, is that for the complete strip (so each LED would have a drive current of 66mA)? I'll got and try it!

[diif]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Try each set of 14 at a time. 42v at 200mA

[budm]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Can I see good clear straight shot of the LED power supply?
This panel has 6 LED strings, the two brown wires are the Anode of the 6 LED strings are tied together and connected to the LED Boosted Voltage power supply, the Blue wires are the Cathode return for each one of the 6 LED strings, each return wire is connected to the PWM controlled MOSFET for maintaining the constant current, there 3 Dual-MOSFET 8-pin chip right next to the LED connector. You need to keep black probe of the meter on the chassis and red probe on one of the Blue wire then turn on the TV to see what you get, then turn off the TV and repeat ehe same test on the other 5 blue wires.

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Here's the LED driver.

Returning to the LED strips themselves, my bench top power supply only goes up to about 30V so I cannot test each string of 14 LEDs using 42V limited to 200mA. However I have tested each individual LED and they all work but the IV characteristic of the individual LEDs was very strange. I had to bias them with at least 5.1V forward voltage before they light up individually (with the power supply leads directly across each LED one at a time). The the current has to be limited to about 2mA otherwise they go dangerously bright.

Help! what's going on with these LEDs! I checked the voltage with a second meter and it's definitely correct.

[budm]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

They are dual LED per package.

[Diah]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

SMT LED testing not about lighting or not.. i write before the critical point when the built in Opposite Diode for FW currents shorted or open..

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

Can I see good clear straight shot of the LED power supply?
This panel has 6 LED strings, the two brown wires are the Anode of the 6 LED strings are tied together and connected to the LED Boosted Voltage power supply, the Blue wires are the Cathode return for each one of the 6 LED strings, each return wire is connected to the PWM controlled MOSFET for maintaining the constant current, there 3 Dual-MOSFET 8-pin chip right next to the LED connector. You need to keep black probe of the meter on the chassis and red probe on one of the Blue wire then turn on the TV to see what you get, then turn off the TV and repeat ehe same test on the other 5 blue wires.

I tried this and the blue wires all seem to be at a floating voltage. There isn't any distinct change in the meter reading when the power is switched on. I did this with the LED panels wired up but the TV screen panel disconnected. Everything else was connected.

[lamlash]

Re: Panasonic Viera TX-L32E3B won't power up, green LED flashing

SMT LED testing not about lighting or not.. i write before the critical point when the built in Opposite Diode for FW currents shorted or open..

I need to learn more about this - could you send me a link to that post please?