40" Philips 40pfl4706/f7 Mother board replacement

[muehring]

Hi,

I have a Philips LED TV that stopped working after I installed a software update. I took it to a repair shop because the warranty needed an estimated repair cost and they said I need a new mother board. I found a replacement mother board online. I'm wondering if replacing the mother board is as easy as taking the old one out and putting in the new one. Are there any other steps I need to take after replacing?
I have hobbyist level electronics experience. I think troubleshooting the mother board would be too much for me since it's SMD.
Any help is appreciated. Thanks!

[tom66]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

It is pretty much that simple.
However, if the diagnosis of the TV place is wrong, then you would be out the cost of the motherboard.
If you have warranty, why not use it? Is there any extra charge?

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Great, thanks for the quick reply! I'll give it a shot. I did use my credit card's extended warranty. They cut me a check for the cost of the repair and I used that for a new TV. The mother board's not cheap, but if it works it'll be a good deal.

[tom66]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Would you perhaps like to diagnose the fault first? You will need a digital camera and digital multimeter.

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Yeah, that would be great. I have a digital camera and DMM. I can post some pics today.

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Here are some pics
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I can take some more detailed pics if needed.

[tom66]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Can you read off the legend next to the connector (going to the main board) on the right of this image?
http://img.photobucket.com/albums/v6...g/IMG_0891.jpg

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Is this the legend you need?



Here is the legend:
BL-ON
NT_Dim
P-ON
GND
Ext_Dim
STB5-3V
GND
GND
GND
GND
P-ON12V
P-ON12V
P-ON12V
P-ON12V

The other connector's legend (the one connecting to the smaller board in the middle with the two red caps) is:
Ext_Dim
NT_Dim
BL_On
ERROR_OUT
GND
GND
GND
GND
GND
GND
+24Vb
+24Vb
+24Vb
+24Vb
+24Vb

[tom66]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Check pin STB5-3V for 5.3V standby: Red probe touching metal around appropriate pin, black probe on the chassis.

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

I'm getting 5.226V on that pin.

[tom66]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

That's good, then. Next step, check the P-ON pin and the P-ON12V pins.

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Thanks! I'm not getting any volts on P-ON or the P-ON12V pins in standby mode.
With the power on I'm getting 3.296v on P-ON and 12.23 on each of the P-ON12v pins.

[tom66]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

This confirms that portion of the power supply is operating correctly; most likely the rest of the PSU is too. Can you next check BL-ON, NT_Dim, Ext_Dim and the +24Vb line, on either connector, just to verify the operation of the PSU and other parts.

If the voltages are good, but the BL-ON is missing, then I would diagnose a main board fault. However, if the 24V is missing or the BL-ON is present (with good 24V) then I would diagnose a power supply or backlight driver fault.

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Thanks again! I'm getting .005V on the BL-ON, .019V on NT_Dim, .005V on Ext_Dim and 24.94V on all the +24Vb pins.
The screen actually turned on for a moment when measuring these pins. I think it was on the blue philips screen.

[tom66]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

The main board is not turning on the backlight, so the main board is likely at fault. You may find connecting BL-ON directly to 12V using a 2.2k ohm resistor will fix your problem; the screen might flicker a little during boot up but if the TV is displaying video, it should be usable.

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

I just placed the order for a new mother board. I don't trust myself to do a solid enough job of wiring the BL-ON to 12V.
Thanks for walking me through the trouble shooting! I learned a lot.

[muehring]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Update - I received the new mother board today. Hooked it up and the TV works great! $70 for the new mother board. Not bad. The repair shop was asking for over $300 for the part and labor. Thanks again Tom!

[tom66]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Glad to hear, not too bad price for the main board.

[samehms]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Hi, I got the same exact TV, but my TV just stopped working. It has no power at all using the remote or the power button. Should the steps mentioned above work in my case? Will testing the output voltage help even there is no response from the TV at all? Thanks.

[ion4449]

Re: 40" Philips 40pfl4706/f7 Mother board replacement

Great tutorial...I have same tv...problem is power continuously recycles after logo screen...my voltages are however double those or more than those on the legends...I disconnected the backlight inverter and still had the higher voltage readings on the power board...your thoughts would be greatly appreciated....Thanks, Barry