LG 42PJ350 clicking (yes another one)

[The_Todd]

Hello guys,

Have a problem with another lg plasma board not working, I have gone through all the other osts about this but i am stumped.

So basicly the tv turns off and on with no picture. Red light comes on then fades. And just clicking continuiously like the tv keeps trying to start.

So this is what i have found so far....

All caps are good.
All diodes are good,and sscottys (as far as i can tell)
All fuses good
I did replace one of the big polly capacitors but there is no difference.
Connecting or disconecting all y-z ect boards makes no difference, however with connected the boards hum for a second. With mainboard also disconected nothing happens.and tried removing all other conections off main board.
The AC detect seems to be fine, (4.5V)
The resistors seem to be fine but the 2 super low resistance ones are hard to mesure.
All solder joints fixed.
There is NO va or vs voltage but there is 5v voltage

There is 2 more things i can think off..

Thermal resistor issue, there is a very small smd one on the board reading about 10M resistance, that sound right? There is no marking on it.

Also read there could be a firmware corruption? How to test that?

Cheers, and sorry if i missed anything already

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

Doing more testing around the board...

There is a R2A20117 right neat the va/vs output wich i can tell controls the mosfets. It is not getting power :/

Now can somone who is truly wise explain, does each part of the main baord work kind of independantly, or is there a main process that turrns each chip or cucuit on when conditions are met?

[tw2005]

Re: LG 42PJ350 clicking (yes another one)

where is this 10Mohm SMD? I got a 50 pulled part, don't expect much difference between the
boards. Presume you checked the ceramic resistors? What did they read?

I'm in the middle of a PX550 PSU with bad resistors it seems.

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

Weird now the therm is correct.

The resistors are corect i think..

The two 22R read about 22.5r so thats fine

The other 3 are like r200, r050, r030, im asuming they read as 0.X values? Are ok I think my multimter has trouble reading that low.
Also some of the optocouplers are reading very high resistance (when off) is this normal? Like MR. They are also all but faded so i cant tell what the values are :/

Also note im using a BM235 so I have faith my milimet is right

Cheers

[tw2005]

Re: LG 42PJ350 clicking (yes another one)

Weird now the therm is correct.

The resistors are corect i think..

The two 22R read about 22.5r so thats fine

The other 3 are like r200, r050, r030, im asuming they read as 0.X values? Are ok I think my multimter has trouble reading that low.
Also some of the optocouplers are reading very high resistance (when off) is this normal? Like MR. They are also all but faded so i cant tell what the values are :/

Also note im using a BM235 so I have faith my milimet is right

Cheers

Rxx is generally 0.xxx so 3r5 would be 3.5ohms, r5 would be 0.5 ohms. not sure about the optos. I'm on a goose chase too. Amazing what a broken test does to meter readings! Starting to hate my LG PSU issie.

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

Ok after finally finding a "training manual" this is starting to make sense.

So there are 4 main output

17v = yes
M5v = yes
Va = no
Vs = no

And the va/vs is powered buy the same smps cucuit and transformer. And guess what? The chip that controls that is not getting power to run... Hmmm....all the voltages are behind the mosfets, but nothing to tell them to run.

The curcitry that suplies that is rather hairy..... A ton of resistors, and a componet called a
D1347 some high powered transistor, i think im getting close.

[tw2005]

Re: LG 42PJ350 clicking (yes another one)

Ok after finally finding a "training manual" this is starting to make sense.

So there are 4 main output

17v = yes
M5v = yes
Va = no
Vs = no

And the va/vs is powered buy the same smps cucuit and transformer. And guess what? The chip that controls that is not getting power to run... Hmmm....all the voltages are behind the mosfets, but nothing to tell them to run.

The curcitry that suplies that is rather hairy..... A ton of resistors, and a componet called a
D1347 some high powered transistor, i think im getting close.

Maybe , but I'm hitting the sack. Just got mine running. Riddled with cracked solder joints.

probably worth going over yours with a fine tooth comb since they are of the same era. FETs, transformers, you name it I found broken and really cold joints in places.

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

to add to this M_ON pin is what turns on the circuits to supply va/vs, even when jumper-ed there is no difference. i need to work out how is the curcuit does this? does this literally turn on or off the power to the IC's that control this? or does it send a "turn on" command?

As for the octos, the question are they just used for feedback or are they part of the startup process??

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

Maybe , but I'm hitting the sack. Just got mine running. Riddled with cracked solder joints.

probably worth going over yours with a fine tooth comb since they are of the same era. FETs, transformers, you name it I found broken and really cold joints in places.

yeah you may be right, tommorow I might try a powered test, and follow the power track backwards. ill find this join.

Also generally these are shit PCB's, even when soldering a single join, the heat causes the top layer to separate from the board :S

[tw2005]

Re: LG 42PJ350 clicking (yes another one)

yeah you may be right, tommorow I might try a powered test, and follow the power track backwards. ill find this join.

Also generally these are shit PCB's, even when soldering a single join, the heat causes the top layer to separate from the board :S

Yeah, volcanic. Not designed for rework, they look like they're made from recycled material.

i'd go over all the joints first, you may get lucky. I've seen Samsung PSU boards detonate the FETs when the solders are broken.

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

Hey stupid question, what would be this guys value?

[attainteddragon]

Re: LG 42PJ350 clicking (yes another one)

starting from the brown side, i got 1.06m .5%

i hate colour codes.

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

Realy? It reads about 10M on multimeter, it connects the main DC negative to hot ground

[tw2005]

Re: LG 42PJ350 clicking (yes another one)

Realy? It reads about 10M on multimeter, it connects the main DC negative to hot ground

Yeah, weird coding but 10 Meg, Mine reads about 9.8 Meg in cct

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

Ok cool,

And this ine only reads about 4K in curcit, what should this read?

Cheers

[dick_barton]

Re: LG 42PJ350 clicking (yes another one)

Looks like a 1 Mohm but best to lift one leg out of circuit to measure.

[The_Todd]

Re: LG 42PJ350 clicking (yes another one)

Ok so over 9001 hours of reviews and reading, im fairly certain the problem lies with the main VA/VS supply curcuit (or the power supply to it).

The L6599A give a very strange and eratic pulse signal to the mosfet, (mosfets are ok btw) and the of course stops and "click click" reset, and there is no output at all from transformer, and from what i can mesure no where near enough voltage going into the transformer.

Now can comone have a look at the attached curcuit and expalin or point me in the direction of how the dual mosfets (Q801 &q802) work together to run the transformer, as So Far i only have seen single drivers.

Cheers,

[cmagavilano]

Re: LG 42PJ350 clicking (yes another one)

1.05M Ohms .5% r805