Philips 42PFL7422D/37 Backlight Issue

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

Okay, let's try this.

The pins are numbered 1 through 10 on the pcb. Last pin = 10.

a) black probe on pin 1, red on pin 2 - record ohm
b) black probe on pin 1, red on pin 3 - record ohm
c) black probe on pin 1, red on pin 4 - record ohm
d) etc
e) black probe on pin 1, red on pin last - record ohm
f) black probe on pin 2, red on pin 3 - record ohm
g) black probe on pin 2, red on pin 4 - record ohm
h) etc
i) black probe on pin 2, red on pin last - record ohm
j) black probe on pin 3, red on pin 4 - record ohm
k) etc
l) finally, black probe on pin last-1, red on pin last - record ohm

What we are doing is trying to measure every possible pin combination to find the secondary pins. It shouldn't take more than 10 minutes to do this.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Thanks retirecaps - I think I was typing out my long reply above before I saw your post. The above readings are with S1 and S2 on opposite sides of the transformer. On T1, S1 is the outer most corner pin (where I have the black probe on the Master_old picture above), and S2 is the first pin from the left on the opposite side. I did not grab a picture of me testing like that, but I can if needed.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Thank you for all the newbie patience. I've attached a picture with the pins labled. Here are my combo testing results. All combinations not listed read as open/OOR:

Old Master T1:
Pin 2-4: 8.49k Ohms
Pin 2-5: 8.49k Ohms
Pin 2-6: 8.47k Ohms
Pin 2-7: 8.48k Ohms
Pin 2-8: 23.3 Ohms
Old Master T2:
Pin 1-2: 0.3 Ohms
Pin 1-4: 8.39k Ohms
Pin 1-5: 8.39k Ohms
Pin 1-6: 8.38k Ohms
Pin 1-7: 8.47k Ohms
Pin 1-8: 23.4 Ohms
Pin 2-4: 8.45k Ohms
Pin 2-5: 8.46k Ohms
Pin 2-6: 8.46k Ohms
Pin 2-7: 8.45k Ohms
Pin 2-8: 25.8 Ohms

Old Slave T1:
Pin 2-4: 9.07k Ohms
Pin 2-5: 9.08k Ohms
Pin 2-6: 9.08k Ohms
Pin 2-7: 9.07k Ohms
Pin 2-8: 23.3 Ohms
Old Slave T2:
Pin 1-2: 0.3 Ohms
Pin 1-4: 9.08k Ohms
Pin 1-5: 9.05k Ohms
Pin 1-6: 9.06k Ohms
Pin 1-7: 9.07k Ohms
Pin 1-8: 25.4 Ohms
Pin 2-4: 9.07k Ohms
Pin 2-5: 9.05k Ohms
Pin 2-6: 9.05k Ohms
Pin 2-7: 9.04k Ohms
Pin 2-8: 23.2 Ohms

I got the same combination of results for the new boards I ordered, except they were in the 7.1k range.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Other Pin combos if needed:
Old Master T1:
Pin 4-5,6,7: 0.3 Ohms
Pin 4-8: 8.39k Ohms
Pin 5-6,7: 0.3 Ohms
Pin 5-8: 8.40k Ohms
Pin 6-7: 0.3 Ohms
Pin 6-8: 8.37k Ohms
Pin 7-8: 8.41k Ohms
Old Master T2:
Pin 4-5,6,7: 0.3 Ohms
Pin 4-8: 8.34k Ohms
Pin 5-6,7: 0.3 Ohms
Pin 5-8: 8.37k Ohms
Pin 6-7: 0.3 Ohms
Pin 6-8: 8.39k Ohms
Pin 7-8: 8.35k Ohms

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

Here are my combo testing results. All combinations not listed read as open/OOR:

All those readings are within 3% of each other. The 8K readings are what I expected.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Thanks Retiredcaps. Does that mean that the inverters sound like they're probably good? I can try and do the rolled up paper test and listen for anything strange out of the transformers.

I'm guessing these inverters are going into some type of lock down mode and cutting the power off intentionally. After reading that other linked post, my best thought is to try and inspect the ccfl bulbs. I didn't see any results from the previous thread poster on how that turned out for him, but hopefully it will be a clue into my next steps.

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

Does that mean that the inverters sound like they're probably good?

Yes, those readings indicate they are likely good. Plus, you already ordered a new master/slave.

I'm guessing these inverters are going into some type of lock down mode and cutting the power off intentionally. After reading that other linked post, my best thought is to try and inspect the ccfl bulbs.

The pwm chip operates on an "all or nothing" premise. All the ccfls work or none at all.

PlainBill explains constant current AC source with protection on post #113 at

https://www.badcaps.net/forum/showth...?t=8589&page=6

BTW, on the same page, if you read the other posts, you will see alexanna talk about the return wiring on the ccfls (for computer monitors, not TVs) breaking down. You could have the same situation on your TV?

https://www.badcaps.net/forum/showth...?t=8589&page=6

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

I manned up and finally took the tv all the way apart, and it looks like I've got 3 ccfls that are bad. I've attached pics. This brings me to my next set of amateur quetions:

1) Can I connect back up all the powers (less the tcon and LCD connection) and powe the tv up to see which bulbs will flash on during that initial 2 secs?

2) Does anyone know a good place to find replacement bulbs? From what I've googled, I can't easily find a part number, just sites with sizes listed. These are 4mm diameter, and I'm not sure on the length since these don't have to be soldered and I don't know where to stop the measurement. They look to be between 940-950mm.

Thank you guys for this forum! I'm feel like I'm learning a ton.

[tom66]

Re: Philips 42PFL7422D/37 Backlight Issue

I manned up and finally took the tv all the way apart, and it looks like I've got 3 ccfls that are bad. I've attached pics. This brings me to my next set of amateur quetions:

1) Can I connect back up all the powers (less the tcon and LCD connection) and powe the tv up to see which bulbs will flash on during that initial 2 secs?

2) Does anyone know a good place to find replacement bulbs? From what I've googled, I can't easily find a part number, just sites with sizes listed. These are 4mm diameter, and I'm not sure on the length since these don't have to be soldered and I don't know where to stop the measurement. They look to be between 940-950mm.

Thank you guys for this forum! I'm feel like I'm learning a ton.

1.) Yes, but be careful not to touch either end of the bulbs as they are energised with high voltage (around 3kV, each.)

2.) ccflwarehouse.com gets tossed around a lot. Also ebay. Also a broken screen TV of the same size can be a good source of bulbs. I've got a collection of bulbs from a 32" Philips (about 20) should a faulty backlight TV come in.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Thank you Tom. I'll work on getting it half together and testing. I've been keeping my eyes open on craigslist, but so far, no luck with and broken 42" tvs.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Ding Ding. Four bad bulbs - wish it was less, but at least I know what to look for.

Tom - any tips on unseating these bulbs from their holders? The don't seem to want to pop out by hand easily.

[jthi]

Re: Philips 42PFL7422D/37 Backlight Issue

Pic

[retiredcaps]

Re: Philips 42PFL7422D/37 Backlight Issue

Ding Ding. Four bad bulbs

For the ones that are bad, carefully check the soldering on the ccfl bulb ends and the caps that are attached to it.

Check for poor solder joints with power off and TV unplugged!

[PhilipsKSI]

Re: Philips 42PFL7422D/37 Backlight Issue

I had a similar issue and while searching on google ended up joining this forum. What was the conclusion for this issue?

[PhilipsKSI]

Re: Philips 42PFL7422D/37 Backlight Issue

If anyone wants a 42PFL7422D/37 Philips TV for cheap, drop me a line. I found this one too difficult to open what to speak of repairing. It's working fine under HDMI, A/V, component, and side A/V. But for coaxial you have to first start up in one of the other input modes and switch after it powers up.

It has a couple of burnt out backlights so picture is overall slightly dimmer than it should be.

[120volts]

Re: Philips 42PFL7422D/37 Backlight Issue

I just fixed two of the 42PFL7422D/37 with the same (No back-light) about six weeks ago.

Both had shorted transistors on the slave inverter board.

I first tried replacing the shorted transistors, the back-light then turned on but the transformers were getting very hot.

I ended up replacing both master and slave boards in both TVs.

$49 for the set of boards on eBay.

They're both working well now.

[PhilipsKSI]

Re: Philips 42PFL7422D/37 Backlight Issue

Too many screws to just open this unit and some of these screws are inaccessible with the tools I have since there's a metal plate that's obscuring some screws. So I haven't yet opened up the unit yet although I do have the T10 Torx screwdriver for most of the screws.

[Zoli77]

Re: Philips 42PFL7422D/37 Backlight Issue

Hi everybody,

I read this blog and I have a problem with LCD TV a 42LG2000. This TV similar to the Philips 42PFL7422D/37. I can turn On the TV, after the backlight turn On approximately 5 secundum then the backlight turn Off. I checked the power supply, it is OK. I checked inverter voltage they are OK. On the inverter Backlight On voltege is OK until the TV On. I changed the elektrolit capacitor on the inverter but the problen remains.
On the master inverter at trafo keramic capacitor (red circle) was carbonised. I changed it but the problen remains.
I checked inverter transformators (T51.0166.211)
Master inverter
Primer side
T1: 29,3 Ohms
T2: 29,3 Ohms
Secondary side
T1: 0,3 Ohms
T2: 0,3Ohms

Slave inverter
Primer side
T1: 29,3 Ohms
T2: 29,3 Ohms
Secondary side
T1: 0,3 Ohms
T2: 0,3Ohms

Master inverter: VIT71053.54
Slave inverter: VIT71053.55

I checked CCFL lamp in the LCD sreen, all CCFL lamp operating full white light

Can I check anything