Panasonic TH-L32X20S Protect, Power Led blingking one times.

[bangjay]

Dear Master,

Please Help,..

I have Panasonic TH-L32X20S LCD TV, the problem is the tv suddenly turns off after a few minutes and the power led blinking one times.

Based on information from the service manual it is a problem with BACK LIGHT_SOS.

I have checked the voltage, Stby 6Vtuner is good, 3.3V is good, 12V is also good, 17V reads 18V and 32v reads 30V sometimes 32,V 34V, back to 30V,

I did the test before the TV dead protect.

I send the photo of P Board and the inverter circuit schematic.

[nomoresonys]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

Heat up those electrolytic capacitors on the powerboard with a hairdryer, see if the tv stays on longer.

[dick_barton]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

It may be a problem with the CCFL tubes. While it is running is the image on the screen darker along the horizontal. I would use a usb stick with colour images to check.

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

Thank you for your attention. how to check if ccfl has a problem.
I have tried turning on the tv without the ccfl lamp by removing the socket to the ccfl lamp, but within a few minutes the tv turned off again.

I suspect a problem in the inverter, but I'm still not sure.

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

Heat up those electrolytic capacitors on the powerboard with a hairdryer, see if the tv stays on longer.

Thank you, I will try it and will update later

[dick_barton]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

I would use a usb stick with some images on. For example a white or green image and then look very carefully at the image when being displayed.
Do not disconnect any connections to the CCFL lamps.

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

It may be a problem with the CCFL tubes. While it is running is the image on the screen darker along the horizontal. I would use a usb stick with colour images to check.

Thank you for your attention. how to check if ccfl has a problem.
I have tried turning on the tv without the ccfl lamp by removing the socket to the ccfl lamp, but within a few minutes the tv turned off again.

I suspect a problem in the inverter, but I'm still not sure.

[dick_barton]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

Check the dc voltage on pin 19 and pin 20 of IC7800 before and after the backlights go off.
They are the protection High and protection Low signals to the IC and are fed back from the CCFL's

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

Check the dc voltage on pin 19 and pin 20 of IC7800 before and after the backlights go off.
They are the protection High and protection Low signals to the IC and are fed back from the CCFL's

Ok, I will check it soon and i will notify you

thank you

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

Check the dc voltage on pin 19 and pin 20 of IC7800 before and after the backlights go off.
They are the protection High and protection Low signals to the IC and are fed back from the CCFL's

Hi dick_barton

I have tested the voltage on pin 19 and 20.

When in standby mode the voltage is
Pin 19 = 0.11V and Pin 20 = 0.0V

then when the tv is on
Pin 19 = 2.28V and Pin 20 = 1.56V

and when the tv turn off protect
Pin 19 = 0.04V and Pin 20 = 0.01V.

I noted that when the TV was on, the voltage on the Pin 20 and 19 dropped to 0.98V for several times and it happened so fast.

What do you think about the results of this test?

Thank you.

[dick_barton]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

Those two pins are feedback from the tubes and I would have expected them to be roughly equal in voltage. You do say that the voltage dropped fast several times. Did this drop affect the backlights, that is did they blink.

I would next check the voltage on pin2 (Alarm). This pin is what triggers the SOS and shuts down the set. Can you give the voltage when the set is running and as the backlights go off.

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

Those two pins are feedback from the tubes and I would have expected them to be roughly equal in voltage. You do say that the voltage dropped fast several times. Did this drop affect the backlights, that is did they blink.

I would next check the voltage on pin2 (Alarm). This pin is what triggers the SOS and shuts down the set. Can you give the voltage when the set is running and as the backlights go off.

Yes, the drop has an effect on the back lights, they flashing when the voltage drops.

This is the data from pin 2 on the IC STR-H3475
if standby mode the voltage is 3.3V
when the set is running the voltage is 0.07V
and when the set is off protect the voltage is 3.29V.

[dick_barton]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

What voltages do you have at test points TP7800 through to TP7807 while running and does one of them have significantly different reading to the others.

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

What voltages do you have at test points TP7800 through to TP7807 while running and does one of them have significantly different reading to the others.

Hi dick_barton, thank you still helping me,

this is the voltage from TP7800 to TP7807.
TP7800 = 1.10V
TP7801 = 1.08V
TP7802 = 1.10V
TP7803 = 1.08V
TP7804 = 1.07V
TP7805 = 1.05V
TP7806 = 1.10V
TP7807 = 1.11V

[dick_barton]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

TP7800 & TP7801 1.10V & 1.08V
TP7802 & TP7803 1.10V & 1.08V
TP7804 & TP7805 1.07V & 1.05V
TP8706 & TP7807 1.10V & 1.11V

The only odd reading is the last set but there's nothing that stands out as obvious to me.

With the set off can you measure the resistance between pins 2 & 3, 5 & 6, 7 & 8 of each of the transformers T7801 to T7804 to see if there is any obvious difference in readings.

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

TP7800 & TP7801 1.10V & 1.08V
TP7802 & TP7803 1.10V & 1.08V
TP7804 & TP7805 1.07V & 1.05V
TP8706 & TP7807 1.10V & 1.11V

The only odd reading is the last set but there's nothing that stands out as obvious to me.

With the set off can you measure the resistance between pins 2 & 3, 5 & 6, 7 & 8 of each of the transformers T7801 to T7804 to see if there is any obvious difference in readings.

Pin 1 connects to pin 2 and pin 3 connects to pin 4
so i measured pins 1 & 3 pins 5 & 6 and pins 7 & 8
this is the measurement result:
T7801 = 1&3 is 0.005, 5&6 is 1.015, 7&8 is 1.016
T7802 = 1&3 is 0.005, 5&6 is 0.999, 7&8 is 1.002
T7803 = 1&3 is 0.005, 5&6 is 1.018, 7&8 is 1.018
T7804 = 1&3 is 0.005, 5&6 is 0.990, 7&8 is 0.993

Please correct me if my measurement method is wrong, i am using digital multimeter with 200 Ohm for pin 1&3 and 2K for pin 5&6, 7&8.
thank you

[dick_barton]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

I believe those readings to be OK. I can't think of anything else to try at this time.

I would wait and see what help others could offer you at this point.

My feeling is that you have a tube failing which may be dimmer than the others causing the protection to activate.

If it was my set I would carefully lift the panel and check the tubes are all in good condition and none of them are dim when you switch on.

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

I believe those readings to be OK. I can't think of anything else to try at this time.

I would wait and see what help others could offer you at this point.

My feeling is that you have a tube failing which may be dimmer than the others causing the protection to activate.

If it was my set I would carefully lift the panel and check the tubes are all in good condition and none of them are dim when you switch on.

dick_barton, i have a new progress, today i am trying to lift the transformer on the inverter block and measure it for each pin. all transformers have the same value. pins 5 & 6 = 1.025 and pins 7 & 8 = 1.025.
then I soldered it again to the board and turned on the tv. after waiting for about 30 minutes the tv is still on. but not even 1 hour the tv turns off again.
Previously, this TV could only be on for about 5 to 10 minutes
I suspect the components around the transformer, maybe the capacitor or resistor is half damaged.

do you have any more ideas

[dick_barton]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

It may have been that you had a poor solder joint on the transformer which you have resoldered.

Resolder all the transformer joints and check for any solder joints that do not look good especially around IC7800

[bangjay]

Re: Panasonic TH-L32X20S Protect, Power Led blingking one times.

It may have been that you had a poor solder joint on the transformer which you have resoldered.

Resolder all the transformer joints and check for any solder joints that do not look good especially around IC7800

Ok, I'll do it.