Phillips LCD Model #42PFL7422D/37

[Sly_Boogy]

Re: Phillips LCD Model #42PFL7422D/37

Alright, that picture sucked. These are a little better. There was more of that grayish mark/stuff around the SMD (burned solder?), but it came off when I grazed it with the probe.

[Sly_Boogy]

Re: Phillips LCD Model #42PFL7422D/37

Whoops, image didn't post. Tell me if you can't see it well enough, I'll try and get a better one.

[dskall]

Re: Phillips LCD Model #42PFL7422D/37

Need some pictures of the area

[Sly_Boogy]

Re: Phillips LCD Model #42PFL7422D/37

Hello everyone, I purchased a broken TV of this model over the summer in hopes of fixing it, and I have the exact same problem! Same symptoms, same green led lights, clicking, everything. Btw, I didn't see anyone mention this in the thread, but the clicking sound mentioned is when the main board restarts the whole TV.

*Just as a disclaimer, I am inexperienced repairing electronics, and to be honest, electricity confuses me a bit; so bear with me as I might not use all the proper terminology and whatnot. You may also cringe while reading this.*

I have been searching through the repair guide which I linked here from my Google Drive (sorry, max attachment size was 19MB, guide was 23MB) and I found an interesting section under fault finding on page 34:

• Symptom: +1V2, +1V4, +1V8, +2V5 or +3V3 shows a high
level of ripple voltage (audible noise can come from the
filtering coils 5U01, 5U02 or 5U60). Possible cause:
instability of the frequency and/or duty cycle of a dc-dc
converter or stabilizer.
1. Check the resistor 3U32 and 3U7D, capacitors 2U17
and 2U19, input and output decoupling capacitors.
2. Check a.c. feedback circuits
(2U23+2U24+3U55+3U63 for +1V2,
2U6D+2U6E+2U6G+3U6A+3U7E for +1V4 and
2U07+2U08+3U17+3U24 for +3V3), compensation
capacitors 2U25, 2U34, 2U36, 2U37, 2U40, 2U43,
2U68 and 2U6B.

This is interesting because ever since I got the TV, I have noticed audible noise coming from somewhere on the main board. Its a high pitched electronic squeal, I can record it if you'd like to hear it. Now, I do not know what ripple voltage is or how to measure it, but I do know how to test resistors and capacitors.

I first tested resistor 3U32, which is a SMD on the back of the main board. It tested ok (38.7k ohms, rated for 39k), but it looks a little funky. I have attached a picture of 3U32. (sorry I couldn't get a closer shot, if I can find my dang macro lens I'll take a better one.) It has continuity to the next components, but it almost looks burned or unseated, at least compared to the others. For some reason I then plugged in the board, and I touched a probe to the resistor. The squeal immediately became much more intense, as if I had touched an open wound. The board restarted if I recall correctly.

I also noticed that there seemed to be heat coming from this area. I hovered my finger around until I found that the source seemed to be 7U00, a small integrated circuit connected directly to 3U32. I touched the top to feel if it was hot (it was) and the board restarted 2 or 3 times in a row. I made sure I wasn't touching any pins and tried it again with the same result. I've heard that when processors get hot, it sometimes means they are bad, but I don't know if this applies to ICs.

I searched the guide to see what else I could find about 7U00, and it seems like its a fairly important circuit?? Page 142 says it is a MOSFET driver and PWM generator. The paragraph titled "Voltage Booster" on page 142 says that pin 4 should be 18V. I tried to get a voltage reading on pin 4, and as soon as I touched the probe to it, the board restarted continuously, so much so that I couldn't even get a reading on the pin. Pin 4 is directly connected to 3U32. Coincidence? Maybe.


This is where I'm stuck. Like I said, I'm pretty inexperienced, so I don't know where to go from here or what to test next. Does it sound like I may be on to something or am I on a wild goose chase? Maybe I'm just causing a short... Any advice is appreciated, I'm here to learn.

*Full diagram of the main board can be found on page 122; 7U00 and 3U32 are in E2*

[Tayninh55]

Re: Phillips LCD Model #42PFL7422D/37

OK,,,,,,,,,,I'll see what I can find out on the voltages. If you hear a BIG BANG, you'll know what happened! May be a while,,,,,,I've got some other "irons in the fire" as well. Take care!

[budm]

Re: Phillips LCD Model #42PFL7422D/37

The resistor is OK.
You will need to check the DCV at the main power supply connectors next to see what you have and also the 25V HOT Voltage.

[Tayninh55]

Re: Phillips LCD Model #42PFL7422D/37

Maybe the resistor is ok then,,,,,,,,,,on the 2000k scale it shows continuity (000 on meter), the same as when you touch probes together. When I checked the resistor on the 2000 Scale,,,it read 469.

[dskall]

Re: Phillips LCD Model #42PFL7422D/37

Resistor is 470ohm so will have to check it on 2kohm setting

[Tayninh55]

Re: Phillips LCD Model #42PFL7422D/37

They are both really hard to read, the resister and the capacitor. The resistor has the letter (or letters) RJ, or BJ, or could be just a large R, with the number 750 printed on it. Even with a magnifying glass it's hard to make out the letters. The number 750 was larger and very clear.

The capacitor was also hard to read. It looks like: 47 Ohm M 275V~X2 and then under that line it has: 3382MKP50709

No, I don't think I can read capacitance, just have a small multimeter that I purchased at Sears.

[budm]

Re: Phillips LCD Model #42PFL7422D/37

BTW, this model is also known for having blown IC on the inverter boards and they need the modification:
https://www.badcaps.net/forum/showth...ght=42PFL7422D

[budm]

Re: Phillips LCD Model #42PFL7422D/37

OK, R3318 per Q523.1U LA chassis, it is supposed to be 470 Ohms.

[budm]

Re: Phillips LCD Model #42PFL7422D/37

Can you read the resistance as printed on that resistor?
To check the capacitor you will need to check the capacitance, I do not know if your DMM can do capacitance reading or not.

[Tayninh55]

Re: Phillips LCD Model #42PFL7422D/37

I think you were right about that resister. When I checked it on 200 ohm scale, it flashed a number, then went to the 1 at the left of the scale, indicating that it's open. I have a continuity checker that beeps. Touch the probes together, and it beeps,,,,,,,,put a probe on each end of the resistor,,,,,and nothing.

Not sure on the capacitor. Put meter on the 2000k scale and it started out at about 800, and slowly the numbers continued going up.

[budm]

Re: Phillips LCD Model #42PFL7422D/37

OK,,,,,,here's the sticker on the back.

On the resister, can I just release one end of the resistor to check it,,,,,or should I take it out of the board completely?

On the capacitor, should I check it with the power plugged in, for DC voltage, and if so, how do I tell the polarity on it (don't think I've ever checked one like that before) I didn't check closely, but don't remember seeing polarity,,,,,I'll check again.

Thanks again for the guidance!

OK, so it is 42PFL7422D/37 chassis # Q523.1U LA.
I will see if they have the service manual at elektrotanya.com

[budm]

Re: Phillips LCD Model #42PFL7422D/37

You can test it without removing the resistor, that resistor usually goes open circuit when it is bad, it usually has the value between 47~150 Ohms.
The grey cap that the resistor is connected to usually lose its capacitance.

[Tayninh55]

Re: Phillips LCD Model #42PFL7422D/37

OK,,,,,,here's the sticker on the back.

On the resister, can I just release one end of the resistor to check it,,,,,or should I take it out of the board completely?

On the capacitor, should I check it with the power plugged in, for DC voltage, and if so, how do I tell the polarity on it (don't think I've ever checked one like that before) I didn't check closely, but don't remember seeing polarity,,,,,I'll check again.

Thanks again for the guidance!

[budm]

Re: Phillips LCD Model #42PFL7422D/37

https://www.badcaps.net/forum/attach...3&d=1490296060

Check the resistance of the resistor R3318 which is right next to the gray rectangular cap, you also need t check the capacitance of that grey cap.

[budm]

Re: Phillips LCD Model #42PFL7422D/37

Can I see the model number sticker on the back of the TV? I need the chassis number on that sticker.

[Tayninh55]

Re: Phillips LCD Model #42PFL7422D/37

It seems that most of the pins on these boards are not labeled. I plugged it in,,,,,the green lights (standby voltage?) came on for a couple seconds,,,,,then went off. I measured the voltage on the ribbon that goes from power board to main board AT the edge of the power board.
Pin furthest to the left I'll call #8 on the pic of the top of the board,,,,,,#8 pin will be the furthest to right on the pic of bottom of the board.

#8 0 Voltage
#7 0
#6 0
#5 0
#4 0
#3 4.0 Volts
#2 5.0 Volts
#1 0.1 Volts

[Tayninh55]

Re: Phillips LCD Model #42PFL7422D/37

OK,,,,,,here are the pictures of the back of the tv,,,,,,