Funai LF320FX4F Wont Power On

[Gorrillasnot]

Hello all,

Working on a Funai LF320FX4F S/N starts with ME1

When plugged in the standby light blinks 4 times and then is lit solid red.
Pressing the power button on the TV or remote does nothing.
There are no screen flashes or any thing displayed on the screen.
I've measured volts all around the board including diodes D651 and D650 both are 20.9v and D653 and D655 are 12.8v.
All the spots marked 3.3v, 13v, and 21v are withing spec at 3.3v, 12.8v and 20.9v.

I've read in other threads where it is suggested to unplug the PSU to mainboard connector (CN501) and try to power on. When I tried this there was no standby light at all and the power button did nothing.

The only ones that are not within spec are the ones on the right side of the PSU and near the PSU to mainboard connector.
The locations are marked in one of the attached pics (Pic borrowed from another thread uploaded by budm.)
P-ON +21V= 0v
ALL 3.3V = 3.3v
BL-SW = 0v
PROTECT3 = .6v
AMP+13V = 12.8v
ADIM P = 0v

No voltages changed when pressing the power button.

https://www.badcaps.net/forum/showth...=32ME303V%2FF7
This is a thread about a similar TV (also where I borrowed the picture from) with the same problem, but the thread seems to have died with no fix revealed.

From reading the thread linked above since there is 0v for P-ON and 0v for BL-SW it seems that the mainboard is bad and not sending the power on signal to the PSU..is my understanding right?

Is there a specific component on the mainboard I should test and or replace or is it best to just replace the whole board?

Thanks

[dick_barton]

Re: Funai LF320FX4F Wont Power On

Don't know if this will help you.

Power supply Page 34

[Gorrillasnot]

Re: Funai LF320FX4F Wont Power On

Thanks for the manual.
In the troubleshooting section under FLOW CHART NO.7 it says is 13v supplied to the collector of Q656. I don't know which pin is the collector, but the side with the single pin is showing 5.8v and the side with 2 pins from top down is 3.3v and 3.8v.
If you don't get 13v supplied to the collector of Q656 it says to measure the emitter of Q658. Again I don't know what pin is the emitter but from the top down as seen outlined in red in the pic I get 5.8v, 3.3v, and 6.4v.

Next it says to check D653, D654, D655, C654,
C655 and their periphery circuit. I've checked the diodes and they seem ok but i dont know how to test the C654 and C655. My meter doesn't have a capacitance setting.

Does it seem like the problem is in the power board? should I try to replace the caps at C654 and C655?

thanks

[R_J]

Re: Funai LF320FX4F Wont Power On

What voltage do you have on Q653, it should have .6 volts on the base to turn it on, If you have more than 0 volts on the collector, the transistor is not turned on and the power supply is likely only in standby state.
Q653 is located in the upper right corner of the picture

[dick_barton]

Re: Funai LF320FX4F Wont Power On

In your first post you say you

I've measured volts all around the board including diodes D651 and D650 both are 20.9v and D653 and D655 are 12.8v.
All the spots marked 3.3v, 13v, and 21v are withing spec at 3.3v, 12.8v and 20.9v.

But further down you say P_ON+21 = 0 however D651 voltage of 20.9V feeds P_ON+21 so I'm puzzled as to what supplies are missing

I suspect it's only the BL-SW voltage (backlight on) which probably comes from the mainboard which is missing.

[R_J]

Re: Funai LF320FX4F Wont Power On

dick is correct, maybe recheck the voltages right at the plug, the schematic shows what they should be,
1,2 (0V)
3-8 (3.3V)
9-14 (gnd)
15-18 (13V)
19 (gnd)
20-23 (21v)

[Gorrillasnot]

Re: Funai LF320FX4F Wont Power On

Sorry for the confusion.
On the board there are several pins with voltages for P-ON+21v, AMP+13v, All+3.3v and all of those have the correct voltages (locations marked in pic). it's only the pins over by the CN501 connector that are not right (marked with blue square).

I measured Q653 and the side with the single leg measured 3v and the other side with 2 legs both showed 0v.

I was going to try to check voltages at the connector, but it got to dark and I was afraid I would short something out.
It looks like it would be easier to flip the board over and test it but the pins are side by side instead of inline up and down so I'm not sure how to go about testing it.

thanks

[Gorrillasnot]

Re: Funai LF320FX4F Wont Power On

I was able to check the voltages at the plug on the mainboard side at CN3701
All voltages were pretty much right on except the 3.3v at Pins 3 ,5 and 7.
Would this most likely be due to a bad mainboard not sending the 3.3v to turn on the PSU? Can this be fixed at the component level?

Pin 1-2 = 0v
Pin 3 = .6v
Pin 4 = 3.3v
Pin 5 = 0v
Pin 6 = 3.3v
Pin 7 = 0v
Pin 8 = 3.3v
Pin 9-14 = GND
Pin 15-18 = 12.8v
Pin 19 = GND
Pin 20-23 = 20.9v

Thanks

[R_J]

Re: Funai LF320FX4F Wont Power On

The power supply IS turned on (pin6), its the backlight that is not turned on (pin5 & 7) BUT I see pin3 (protect3) is only .6 and should be 3.3. So I think that pin is telling the main board NOT to turn on the backlight because of a fault.
Have you checked the voltage on pin CN1001 (going to the led's)? I wonder if your problem is a bad led in the panel.
I would set up your meter to monitor that voltage on CN1001 pin1, plug in the tv and hit the power button. I bet the voltage comes up for a second then drops down
The voltage should be around 55 volts, if it is higher because there is an open led string, IC1001 will detect the ovp and shut it down.

[Gorrillasnot]

Re: Funai LF320FX4F Wont Power On

CN1001 Pin 1 that has a red wire I get 20.7v on stand by. No change after pressing the power button.
BTW Pressing the power button on the TV itself or remote does nothing. The standby LED doesn't flash or change colors. Its as if the button had not been pressed at all. Almost as if the function button controller board was bad.

Would it be possible to test the LED strip without tearing the TV down further? In other words could I use 5 9v batteries connected in series and power the led strip from the wires at CN1001?

thanks

[R_J]

Re: Funai LF320FX4F Wont Power On

They sell led backlight testers on the internet. I have used a variable bench supply to test them in the past.
I guess you could try 4 batteries and see if they light, then add one more, the problem with using the batteries is there is no current limiting.
The backlight driver is not working (shut down) thats why you only read 21 volts. I would think it would would jump to 50-60 volts when first pluged in, but maybe not
maybe check R1015 (.18 ohm) to make sure its not open, you could make sure ic1001 has 12 volts on its Vcc (pin14)
The other option might be to disconnect the cable going to the main board, then add wires between CN501 pin 8 and pin 6 also pin 8 to pin 5 and see if the backlight comes on, if not also add another wire between pin 8 and pin 7
That setup should turn on the backlight circuit (you wont get the red led as the main is disconnected)

[budm]

Re: Funai LF320FX4F Wont Power On

What is your LCD panel model number?
http://www.shopjimmy.com/funai-u34f4...ps-1-strip.htm

Panel Sticker Number: U34F4XZ, HV320WX2-201?????

[budm]

Re: Funai LF320FX4F Wont Power On

https://www.badcaps.net/forum/attach...2&d=1523985559
So so we have BL-SW signal?
You will have to leave the meter probe on it while turning the TV ON to see if it jumps up for seconds, or stay up >2VDC.

[Gorrillasnot]

Re: Funai LF320FX4F Wont Power On

I went ahead and took the panel off to test the LED strip just to be sure they all worked. It has a single strip with 16 LEDs. Using 5 9v batteries I briefly connected it to the + and - on the strip and all 16 LEDs lit up.

What is your LCD panel model number?
http://www.shopjimmy.com/funai-u34f4...ps-1-strip.htm

Panel Sticker Number: U34F4XZ, HV320WX2-201?????

There's 2 stickers on the back of the TV. 1 says P/N: U34F4XT, S/N: T323291659 and the other says 1EM439757.

https://www.badcaps.net/forum/attach...2&d=1523985559
So so we have BL-SW signal?
You will have to leave the meter probe on it while turning the TV ON to see if it jumps up for seconds, or stay up >2VDC.

J169 BL-SW shows 0v when plugged in (standby) and doesn't change after pressing the power button, still 0v.

R_J: With my skill level (lack of) and the tiny pins I don't know if I could run wires to the pins as you suggested. I'd be afraid I'd short something out.
Instead could I unplug the main board and run a wire from J170 ALL+3.3v to J169 BL-SW?

thanks

[R_J]

Re: Funai LF320FX4F Wont Power On

If the backlights all work then I suspect the fault is either with the power supply or the mainboard, You should be able to connect the wires on the back of the power supply board, on the connector pins, if the backlights com on then the fault would be with the main board

[Gorrillasnot]

Re: Funai LF320FX4F Wont Power On

Sorry for the delay..It's been a busy week.

They sell led backlight testers on the internet. I have used a variable bench supply to test them in the past.
I guess you could try 4 batteries and see if they light, then add one more, the problem with using the batteries is there is no current limiting.
The backlight driver is not working (shut down) thats why you only read 21 volts. I would think it would would jump to 50-60 volts when first pluged in, but maybe not
maybe check R1015 (.18 ohm) to make sure its not open, you could make sure ic1001 has 12 volts on its Vcc (pin14)
The other option might be to disconnect the cable going to the main board, then add wires between CN501 pin 8 and pin 6 also pin 8 to pin 5 and see if the backlight comes on, if not also add another wire between pin 8 and pin 7
That setup should turn on the backlight circuit (you wont get the red led as the main is disconnected)

DMM set to 200 ohm scale R1015 constantly fluctuates..was as high as 160s and as low as 30s..Tested in circuit. Should it be tested out of circuit?
Would pin 14 of IC1001 be the one I have marked in the pic (red arrow)?

If the backlights all work then I suspect the fault is either with the power supply or the mainboard, You should be able to connect the wires on the back of the power supply board, on the connector pins, if the backlights com on then the fault would be with the main board

To connect to the pins on the back of the PSU would I bridge the gaps diagonally by soldering wires to therm? (Like I have marked in the pic)

Another thing I noticed is while I was double checking voltages with the mainboard disconnected from the PSU they measured about half of what they did with the mainboard connected..Is this normal?

thanks

[budm]

Re: Funai LF320FX4F Wont Power On

"Another thing I noticed is while I was double checking voltages with the mainboard disconnected from the PSU they measured about half of what they did with the mainboard connected..Is this normal?" That is normal in STBY mode.

[Gorrillasnot]

Re: Funai LF320FX4F Wont Power On

It's fixed.
I connected the pins as R_J suggested in post#11 and the backlights came on, so that only left the main board as the culprit.
I found 1 on ebay for a DS1 model TV (shopjimmy lists it as an alternate for a ME1) and after I installed it the TV fired right up. woohoo!

What component on the main board is likely the bad part? The eprom?

thanks everyone