Panasonic L24C28X

[dspok]

Hello,

I have Panasonic TH-L24C28x television with power supply unit model no. B109-E09, and Display card model no. 1AA4B10S1000A. Problem is I cannot turn it no, no power on power indicator.
I measured following on CN3.

1. PS-ON = 5.0v
2. GND = 0.0v
3. GND = 0.0v
4. 5V = 5.1v
5. 5V = 5.1v
6. GND = 0.0v
7. 12V = 12.0v
8. 13VA = 13.0v
9. 13VA = 13.0v
10. AGND 0.0v
11. AGND = 0.0v
12. ADJ = 3.3v
13. ON-OFF = 0.0v
14. NC = 0.0v

Power, Menu, Input, Enter/OK, Vol+, Vol-, Ch+, Ch- all have 3.2v
I have no idea where the problem exists but I suspect problem is ON-OFF or NC pin.

Btw there was no voltages on above pins, a 3-leg mosfet K4100 in which pin1 and pin3 was shorted, searched from diagram somewhere found that it is supposed to be a N-Channel mosfet, I counldn't find same part number so I changed with similiar type of N-Channel mosfet and above voltages were present.

Any ideas to solve this problem please.

[CapLeaker]

Re: Panasonic L24C28X

Cording to this the tv is on, but the backlights are not getting turned on by the main board. So you have a main board problem

[dspok]

Re: Panasonic L24C28X

Cording to this the tv is on, but the backlights are not getting turned on by the main board. So you have a main board problem

Any idea to fix it? Or should I change main board?
Btw there is no sign of life in power indicator.

[CapLeaker]

Re: Panasonic L24C28X

check the PSU out first. Unhook everything from the PSU and just leave the backlights connected. You need two 1k ohms resistors and solder one between STBY voltage and PSon, the other between Stby voltage and BLon. Plug the psu in and all the voltage rails should be up and the backlights should be on.
Repairing main boards like that is hard and you need proper smd rework equipment. I am not saying it can't be done, but it is heck easier to get a new main board, than investing in all that time troubleshooting, parts etc into the old board that acts like that.

If that test passes, go ahead and get a new main board.

[dspok]

Re: Panasonic L24C28X

I understand STBY voltage is on/off but what is BLon?

[marty_cam]

Re: Panasonic L24C28X

I would assume the pin which is labelled BL-on for (backlight on)

[CapLeaker]

Re: Panasonic L24C28X

I understand STBY voltage is on/off but what is BLon?

your BLon is in this case the "on-off" pin.

[dspok]

Re: Panasonic L24C28X

Hey, now I 'm able to turn it on but shuts down automatically after 1 minute or half.

[CapLeaker]

Re: Panasonic L24C28X

Hey, now I 'm able to turn it on but shuts down automatically after 1 minute or half.

explain. Does it work normal for that time period?

[dspok]

Re: Panasonic L24C28X

explain. Does it work normal for that time period?

Turns power LED on, remote power button pressed, Power LED turns green, after few seconds backlight turns on and then TV turns off automatically.

In display board there are two components missing C8001 and R8001. Cannot find value of those components see attached.

[CapLeaker]

Re: Panasonic L24C28X

The capacitor was a electrolytic SMD type. By the size I am guessing something like 16V 10uF. Watch the polarity! So put something in that is at least 16V 10uf. You can put 25V, 35V or 50V, doesn't matter.

The resistor I haven't got a clue. Depends on what pin it goes to on that IC. If we know what IC that is and can find a similar example circuit, we could probably find a resistor that works. If the SMD chip resistor had a 0 (zero) on it, it was just a jumper. Other than that, I guess your gonna be SOL.

[dspok]

Re: Panasonic L24C28X

I think it is firmware chip, I can only read cFeon F80-100HP.

[CapLeaker]

Re: Panasonic L24C28X

The resistor goes to what pin on that IC?
For now just put the capacitor in it's place, instead of this jumper wire, see what happens.