Phillips LCD Model #42PFL7422D/37

[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.

[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

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.

[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

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!

[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*

[dskall]

Re: Phillips LCD Model #42PFL7422D/37

Need some pictures of the area

[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.

[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.