Fixing Phillips LCD TV 37PF7320A

[RobPhotoPro]

Hello everybody!

My friend gave me a broken Phillips LCD TV (37pf7320A) and I am trying hard to fix it.

When I plugged it in, the TV clicked, the green light came up and after about 5 seconds it clicked again and the red light blinked several times. That was it.

So I decided to replace all suspicious capacitors in the power supply. I replaced two 2200uF, five 1800uF and one 1000uF capacitors.

I also noticed, there was a crack in the lower right corner of the board and I repaired three damaged traces.

So now, when I plug the TV, it selfchecks all right (it clicks, green light comes on and then clicks again without any red light). Then, when I try to turn it on, it starts with sound but no picture and after about 10 seconds the TV turns off with red light flashing rapidly. It is unresponsive after that, unless I unplug it and plug it back.

Does anyone have any advice on how to proceed? Can the problem be somewhere else than in the power supply board?

Any suggestion would be very appreciated!

Thank you very much,
Rob (North Carolina)

[Dgtech]

Re: Fixing Phillips LCD TV 37PF7320A

If the board was cracked, I'd suspect someone broke it while moving it or something. Without going so far with this set, take a little while to inspect the screen with a flashlight. You should be able to make out a decent picture behind the darkness. You'll also be able to see of the screen is cracked or not.

If all is OK, then re solder all power board transformers. If this was dropped, the heaviest components will sometimes loosen at the solder joints. Next, check the inverter boards. These are the boards in the photo attatched. Once you locate these, post pics of both the master and the slave.

[PlainBill]

Re: Fixing Phillips LCD TV 37PF7320A

Most Philips TVs announce their problems by flashing the front panel LED in a specific pattern. That information can be found in the service manual. The rapid flashing and 'lock up' certainly implies the TV has gone into protection mode.

PlainBill

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

Thank you for all the comments!

I resoldered both transformers and big capacitors. I checked the screen with a flash light - screen doesn't seem to be cracked anywhere, but there's no picture visible, while the TV is on for a brief moment.

I also checked out the service manual, the cause can't be identified by a flashing code in this case (error 1,2,63).

I checked both inverter boards, nothing suspicious found. If I unplug one or both of them, the TV does exactly the same thing as before. Pics are attached.

I don't know, what else I can do. Any suggestions, please?

[Dgtech]

Re: Fixing Phillips LCD TV 37PF7320A

Check the inverter board Fuse (near the main connector) on both boards, and then also check the capacitors on both boards.

[billansor]

Re: Fixing Phillips LCD TV 37PF7320A

Another thing to be aware of is the fuses... The fuses can be small rectangle smd (surface mounted device) and the power board itself will have some pico fuses. Do check all of those as well.

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

All capacitors on both inverter boards look fine. I'll check the fuses .... including the small pico ones .... I was wondering about these little black rectangles on the solder side of the board..... :-)
Thanks, Dgtech and billansor!

[Dgtech]

Re: Fixing Phillips LCD TV 37PF7320A

You'd have to post pictures of what you mean (little black rectangles). They could be diodes or other components.

By the way, caps can be bad without looking bad. If you have a cap meter or esr meter you can check them out of circuit.

You can also compare transformer resistances from master to slave. This should not vary that much from board to board.

Also, could you post some real close up pics of each inverter board. This could be done in sections. The only reason I continue on with the inverter boards is cause I've had more failures with them than I have with power boards on Philips, LG, Vizio, and Magnavox TV's.

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

You're right, I checked the spare parts list, and the black rectangles are all diodes.
Fuses are good on power supply and both inverters.
I was wondering, when I disconnect one or both inverters, the TV has the same symptoms. Doesn't it mean, the problem is in the power supply board?
Sorry for my unexperienced questions.
I will post close-ups of inverters today.
Thanks a lot!

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

Here are the detailed shots of both inverter boards. First five images is the main inverter board, the other five images is the slave board.
Thanks!

[PlainBill]

Re: Fixing Phillips LCD TV 37PF7320A

I was wondering, when I disconnect one or both inverters, the TV has the same symptoms. Doesn't it mean, the problem is in the power supply board?

Thanks a lot!

No, it means the problem is NOT in the inverters. An inverter fault would either be ignored by the main board, or reported as an error - a flashing LED.

Step 1 is to check the output voltages of the power supply.

Step 2 is to isolate the BL_ON (or equivalent) signal to the inverter and turn the backlights on manually.

Step 3 is to check the voltages on the main board.

PlainBill

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

Thanks, PlainBill. Since I am not that experienced, could you explain in a little more detail?
Step 1 What voltages and where (what pins) I should check on the power supply?
Step 2 How to isolate BL_ON signal and how to turn the backlights on manually?
Step 3 Is the main board in the center or is it the hidden one with inputs and outputs? What voltages to check and where?
Sorry for my ignorance, but I am quite new in this. All I did in the past were a couple or recap jobs, one board replacing and one flyback transformer replacement in the Sanyo CRT TV.
Thanks a lot!

[Dgtech]

Re: Fixing Phillips LCD TV 37PF7320A

Sorry I could not help you further. I'm like the first line of defense where as PlainBill is the special forces. I'm not as experienced as he is with these sets and circuits.

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

Thank you, Dgtech. You made some great and valuable points. I am glad I eliminated some possible causes thanks to you!

[PlainBill]

Re: Fixing Phillips LCD TV 37PF7320A

Thanks, PlainBill. Since I am not that experienced, could you explain in a little more detail?
Step 1 What voltages and where (what pins) I should check on the power supply?
Step 2 How to isolate BL_ON signal and how to turn the backlights on manually?
Step 3 Is the main board in the center or is it the hidden one with inputs and outputs? What voltages to check and where?
Sorry for my ignorance, but I am quite new in this. All I did in the past were a couple or recap jobs, one board replacing and one flyback transformer replacement in the Sanyo CRT TV.
Thanks a lot!

1. All output pins (It may be easier to check the power supply inputs of the various boards. They should be easy to identify them on the schematic).
2. Pins 11 & 12 on the larger input connector are On / Off and Brightness. Measureing the voltages can give a clue as to which is which. (The On/Off will usually be at 3.3 volts to turn the backlights on.) Possible ways to isolate the control line include removing the wire from the connector, cutting the wore in the ribbon cable. The first attempt should be trying to pull it high by using a 1K resistor to 3.3V.

3. The main board is the one inside the metal shield.

PlainBill

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

Okay, this is step 1 - Voltages on Power Supply Board
I numbered pins in the picture attached and the voltages are in Volts (Standby/PwrOn):
pin1 - 5.2/0.29
pin2 - 5.2/5.2
pin3 - 5.2/5.2
pin4 - -75/-75
pin5 - 75/75
pin6 - 0/0
pin7 - 0/0
pin8 - 0/0
pin9 - 0/24
pin10 - 0/24
pin11 - 0/11.8
pin12 - 0/11.8
pin13 - 0/0
pin14 - 0/18
pin15 - 0/18
pin16 - 0/0
pin17 - 0/0
pin18 - -0.5/-18
pin19 - -0.5/-18

Any suggestions?

Thank you!

[PlainBill]

Re: Fixing Phillips LCD TV 37PF7320A

Okay, this is step 1 - Voltages on Power Supply Board
I numbered pins in the picture attached and the voltages are in Volts (Standby/PwrOn):
pin1 - 5.2/0.29
pin2 - 5.2/5.2
pin3 - 5.2/5.2
pin4 - -75/-75
pin5 - 75/75
pin6 - 0/0
pin7 - 0/0
pin8 - 0/0
pin9 - 0/24
pin10 - 0/24
pin11 - 0/11.8
pin12 - 0/11.8
pin13 - 0/0
pin14 - 0/18
pin15 - 0/18
pin16 - 0/0
pin17 - 0/0
pin18 - -0.5/-18
pin19 - -0.5/-18

Any suggestions?

Thank you!

Let's try to identify the functions...

On / Off and power to the power relay
pin1 - 5.2/0.29
pin2 - 5.2/5.2
pin3 - 5.2/5.2

Power to the auxiliary power supply.
pin4 - -75/-75
pin5 - 75/75

Ground
pin6 - 0/0
pin7 - 0/0
pin8 - 0/0

Inverter power
pin9 - 0/24
pin10 - 0/24

Main power
pin11 - 0/11.8
pin12 - 0/11.8

Almost certainly power for audio amp.
pin13 - 0/0
pin14 - 0/18
pin15 - 0/18
pin16 - 0/0
pin17 - 0/0
pin18 - -0.5/-18
pin19 - -0.5/-18

Shoot, this thing has an auxiliary power supply. OK, I've seen that before. This is a more modern version of an LCD TV I repaired a few years ago. It gave me fits.

I'd say the best way to move forward on this is to see if the BL_ON and brightness change when the TV is turned on. I would have to dig through the schematics and identify the signal path through the auxiliary power supply. And there are several other projects waiting for my attention.

PlainBill

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

Hi PlainBill,

Thank you for your help. Does it mean, the power supply board is fine?

It looks this project is a little too much for me. I'll wait for your advice, whenever you have a chance.

Let me know if there is anything else I can do in the meantime.

Thanks a lot!
Rob

[RobPhotoPro]

Re: Fixing Phillips LCD TV 37PF7320A

I attached an image with what I think is the aux power supply. I circled two possible faulty components - 10uF, 450V capacitors and a diode (6113). I measured the diode using ohmmeter and it reads 0, like it's shorted.

Please let me know your thoughts.

Thanks a lot!
Rob

[PlainBill]

Re: Fixing Phillips LCD TV 37PF7320A

I attached an image with what I think is the aux power supply. I circled two possible faulty components - 10uF, 450V capacitors and a diode (6113). I measured the diode using ohmmeter and it reads 0, like it's shorted.

Please let me know your thoughts.

Thanks a lot!
Rob

1. I'm not sure you need my assistance, you are doing well on your own.

2. $%#%@$@!! That looks like the same secondary supply that was used in the TV I repaired. The schematic was a mess!!!

3. Check the diode out of circuit, but a shorted power diode could easily cause the problem.

PlainBill