Philips 55PFL6007K/12 Mainboard

[variTRON]

Hello forum,

I'm fairly new here and this is my first time repairing TVs.

My current project is a Philips 55PFL6007K/12.

Problem: It won't turn on.

Diagnosis: The power supply unit (PSU) seems to be okay. However, when the mainboard is connected to the PSU, there's a humming noise coming from the PSU, and the voltage at the rectifier fluctuates between 285V and 325V.

I think the mainboard is faulty and is causing a load, which is triggering the PSU's protection circuit.

Has anyone had experience with this? What's the most common cause of problems with the 55PFL6007K/12 mainboard? What could I check and measure?

You can reply in Russian. I can understand Russian but can't write it. Thank you in advance.

[igor_me]

" I can understand Russian "
Ну щас проверим :)
Если БП начинает идти в "разнос" при подключении main - ну самое логичное для начала замерить ветки питания, приходящие на  main и огласить тут сопротивления. Ну и само-собой проверить не "кипит" ли что-то на плате, но я полагаю это уже сделано?

[variTRON]

I'll measure the resistance shortly, but I haven't looked for the hotspot yet. I don't have a thermal imaging camera for that.

[variTRON]

ветки питания
1. POK         here I got 2,47V or some mV
2. BL-CTRL
3. BL-DIM
4. BL-ON
5. GND-SND
6. GND-SND
7. +Vsnd      12V OK
8. +Vsnd      12V OK
9. +12V         12V OK
10. +12V      12V OK
11. GND1
12. GND1
13. Standby      here 2,6V and during noise only 30mV
14. 3V3Standby   3,3V OK

[igor_me]

So, i mean not voltage, but RESISTENCE. Voltages looks good. But measure of resistence of power lines will be also usefull.
Also i have idea about problems with main capasitor on PSU. Check it with ESR-meter (and other capasitors on the PSU too, i think)
"I don't have a thermal imaging camera for that".
You don't need any camera, you need just s FINGER ON YOUR HAND :) In russian it calls "finger method" exactly If you can touch some part quiet long (means at least tens of seconds) - ok. If you can't touch it more than 5-10 seconds - in almost all situations it means that part "burning", you have a problem.

[CAIIIA]

something blinked from this table after some time?

[variTRON]

In russian it calls "finger method" - I got it. It´s cool man!

07. +Vsnd - GND-SND = 0,4k and growing
08. +Vsnd - GND-SND = 0,4k and growing
09. +12V - GND1 = 0,4k and growing (I think loading capacitor)
10. +12V - GND1 = 0,4k and growing
11. GND1
12. GND1
13. Standby - GND1 = high resistance = 0.L
14. 3V3Standby - GND1 = 2k-5k (it is changing)

Which capacitors should I check? Can you advise me via circuit diagram?

[variTRON]

something blinked from this table after some time?

Do you mean blinking mode of the front-LED?

[CAIIIA]

Yes

[variTRON]

Yes

I didn´t see anything at my first diagnostic. But I will connect/install mainboard and PSU back and I will check again.

[igor_me]

"Which capacitors should I check? Can you advise me via circuit diagram?"
I mean "main entrance filtering capasitor", in you circuit diagram, as i see, it will be two capasitors - С645 and C646.
Resistances also looks good, as i think. At this step check C645 and C646 first. If you don't have ESR-meter or transistor-tester may be, but have osciloscope with high voltage input or probe unit with divider 1:10 - you can check pulses on this capasitors in work mode...

[variTRON]

"Which capacitors should I check? Can you advise me via circuit diagram?"
I mean "main entrance filtering capasitor", in you circuit diagram, as i see, it will be two capasitors - С645 and C646.
Resistances also looks good, as i think. At this step check C645 and C646 first. If you don't have ESR-meter or transistor-tester may be, but have osciloscope with high voltage input or probe unit with divider 1:10 - you can check pulses on this capasitors in work mode...

I check with LCR-Tester. Nearly 160µF (each 82µF in parallel). I tested without removing from board (I hope this is OK).

Feedback Blinking: LED - there is no blinking mode of LED.

Feedback Hotspot: I cann´t find anything. Only the CPU-cooler is getting warmer after 1min. Cooler is out of "ceramic". So it takes 1min then you feel some warming.

[igor_me]

" I tested without removing from board (I hope this is OK). "
It's not the best way, of course, but for now we can think there is enough, if capasitence close to the right value...
So, if this capasitors good, then ... i want to see picture from oscilloscope. First from +12V power lines with main connected. Do you have it?
So, its strange, if on mainboard you don't have some "burning" components, but on main filter capasitors "jumping" voltage ... strange, strange... may be problems with PFC. Do this TV have PFC? Need to look schematics...

[variTRON]

I don´t have an oscilloscope. I will try to get one.

[variTRON]

For me the 3,3V standby-line is strange. There are two of them and one of them sinks to 35mV during 285V and goes high to 3,3V back when 325V are OK.

[igor_me]

You find some correlation - ok. But 35 mV - it almost nothing. I belive that your problem not in this 3.3v. I think that we must to study question about PFC in this TV first. Also try to find oscilloscope...