Trying to Save - LG 60PH6700 60-inch plasma HDTV - Powers ON but no picture

[KYBOSH]

Saved this beast from the landfill this weekend.
Manfactured July 2013 in Mexico.

I love working on plasma TVs.
Its been a while but I was lucky enough to find 2 this week.

The TV powers on and stays on but no picture. Havent checked for sound yet.
No bulging caps although the insides are pretty dusty and the boards are discolored from many years of high heat.
Will start troubleshooting tonight.

[KYBOSH]

Well in the process of testing I got a bit careless.
With everything connected properly I was not getting proper Vs and Va voltages from the connector at the X-sus leading out to the Ysus,
So i disconnected the harness to the Y-sus and saw proper voltages at the connector leading to it.
Meaning the problem was down at the Ysus or maybe even the buffer board.
So I disconnected both of the buffer boards and tested again.
Unfortunately I absentmindedly didnt bother to fasten the Ysus to the chasis but rather placed the board near where it was supposed to be mounted.
As soon as I plugged it in i heard loud pops. I quickly unplugged the TV and investigated. It seem there were arcs of electricity jumping from the holes where the Y-sus' mounting screw connect to the chassis and the board where the screws go.
Rookie mistake!

When I try to power the TV up now the relays of the power supply just clicks.
So I shorted something on the Y-sus and will need to figure that one out.
If Im lucky the original problem is on the Ysus board and I'll be able to find it while too.

[Biruslapio]

Now you've done it.
Rule 1 of plasmas is always ground all sustain and anything directly linked to the panel.
Steps are:
1. check Y-sus for shorted transistors, if there are, their gate resistor + driver. Diodes and the 2W resistors especially 10, 1 and 2.2 OHMs.
2. check the Z-sus for the same things.
3. test buffer boards panel output pins.
4. logic board for blinking LED.
5. if nothing yet, isolate the main board and do auto_gen test.

[Loanrangie]

Hi new member that came across your post and thought i should join up, i have the same model TV and having similar issues.
I only picked it up Sunday and when i turned it on it took a while but the LG welcome came on then eventually got a picture, nice and clear picture and everything seems to work except subsequent start ups are hit and miss.
Sometimes i get the LG logo,switches on then straight back off or it comes on with no picture. I have more experience other then replacing caps on a TV so figured i may as well start there and see what happens.
Kybosh, have you progressed any further with your diagnostics ?

[KYBOSH]

Hi new member that came across your post and thought i should join up, i have the same model TV and having similar issues.
I only picked it up Sunday and when i turned it on it took a while but the LG welcome came on then eventually got a picture, nice and clear picture and everything seems to work except subsequent start ups are hit and miss.
Sometimes i get the LG logo,switches on then straight back off or it comes on with no picture. I have more experience other then replacing caps on a TV so figured i may as well start there and see what happens.
Kybosh, have you progressed any further with your diagnostics ?

Sitting on my bench at the moment. I have spot checked the Y-sus and saw a few components are shorted and a few are open. Waiting until i have a free evening so I can start dissecting the board and taking stock of what's needed.
So your delayed startups... are they from the lack of the power supply clicking on or does the TV power up but the logo doesnt load for a while? If its the later then it sounds like you may have a mainboard issue.
The fact that you are seeing action on the display is telling that your other boards are working okay.

[Loanrangie]

Sitting on my bench at the moment. I have spot checked the Y-sus and saw a few components are shorted and a few are open. Waiting until i have a free evening so I can start dissecting the board and taking stock of what's needed.
So your delayed startups... are they from the lack of the power supply clicking on or does the TV power up but the logo doesnt load for a while? If its the later then it sounds like you may have a mainboard issue.
The fact that you are seeing action on the display is telling that your other boards are working okay.

It powers on and relay clicks but will either power off again right away or the screen will flicker and not light up, occasionally will get the LG logo or may even get a picture.

[KYBOSH]

It powers on and relay clicks but will either power off again right away or the screen will flicker and not light up, occasionally will get the LG logo or may even get a picture.

Touch up the major solder joints on the power supply.
Specifically the ones on the transformers. Look for bulging capacitors.
Post some pics of it here or start a new thread for personalized assistance from the great gurus of this forum.

The fact that you are getting a startup image (logo) is a good sign as far as your sustains are concerned.

[Loanrangie]

Thanks, if i quickly switch it off and back on again i can get the logo up everytime but then hangs and wont load further, night be a week before i can get it apart and check the boards.

[KYBOSH]

Now you've done it.
Rule 1 of plasmas is always ground all sustain and anything directly linked to the panel.
Steps are:
1. check Y-sus for shorted transistors, if there are, their gate resistor + driver. Diodes and the 2W resistors especially 10, 1 and 2.2 OHMs.
2. check the Z-sus for the same things.
3. test buffer boards panel output pins.
4. logic board for blinking LED.
5. if nothing yet, isolate the main board and do auto_gen test.

Okay!

Finally got some parts in for this baby and started working through the problems.
No joy yet but I am going through in steps and wanted to post things as I go along.
Note: These closeup picks were taken after component replacements so you will not see the original parts in many cases.


First thing I did was try to sort out the Y-Sus.
I found a few components shorted or dead.
On the bottom of the board I found 3 Mosfets (RJP30H2A) with the others reading okay (not shorted).






Topside I found a single bad Gate (RJP30H1) and a single bad resistor (220kΩ).




Everything else on the board tested okay and I didnt see an cracked solder joints so I popped it back onto the chassis to see what would happen and I got nothing.
Power comes on and stays on but no sign of picture.
I see the red light of the digital out port is lit so the mainboard is on and getting power.

I then go to disconnect the buffer boards from the Y-Sus to see if could get the display to light up but again I got nothing.


I went back to have a look at the other sustain and checked the Vs voltage going to the Y and they were strong and steady (200V+).
I checked the other voltages going to the Y and (5V and 15V) and notice that while the 5V was strong the 15V was very low (~5v).
I assume that it should be 15V at all times some something was up.




I looked on the bottom of the board and traced where the 15V led and it took me to a pair of 10Ω resistors that were dead.


I replaced them and looked to see if I restored the 15V but to my surprise the voltage actually dropped to a little over 1V only.
I checked everything (resistors, fets, diodes and gates) on the this sustain and everything seems to look fine. All the caps look fine (visual inspection).

[Loanrangie]

Following with interest, havent done much on mine yet. Our main TV (samsung LA46) decided to play up with clicking relays, quick check on the PS and found 2 bulged caps, replaced all 4 and now as good as ever.
Next up will be looking closer at the LG, would be nice to get it working as a shed TV.

[KYBOSH]

Next up I took the FLIR to the TV to see what I could see.

The mainboard.... nothing out of the ordinary


The Y-Sustain showed some heat (circled in yellow) which i believe were coming from a group of resistors on the underside of the PCB.
R713, R637, R674 and R712. All were 68R3 resistors.


While they looked hot in the picture they were mildly warm to the touch (while the TV was not showing picture) but you can tell from the discoloration (previous post) that this place got really hot.
So I went ahead and changed them even though and all 4 tested true out of circuit.




On the Z-sustain there was a similar group on resistors which (68R3) that shined bright under the FLIR so I went ahead and replaced them as well.





I havent put the board back on yet as I doubt that these resistors are the cause of the problem but I thought it would not hurt to replace them and eliminate them as a suspect as they were likely to be old and worn out from the years of hard work.

Any ideas what I should try next with regards to getting my 15V up and running? I also doubt that is the main issue but it just might be.

[KYBOSH]

Started doing some probing and testing tonight to see what was up with the 15v rail.




I checked the capacitance/ESRs of the caps and they were OK.
I was getting a shorted reading on 2 ceramic side by side caps but when I tested them out of circuit they were fine.
There is an IC right next to it (IC202) and I pulled it off and the short went away.
IC202 reads P155E and its a Toshiba TLP155E which is a gate driver/ octoisolator.
I think this is the first time I am coming across a component like this.
Anyway pins 4, 5 and 6 seem to be shorted across the board.



Gonna have to put this back on the shelf until i can get a replacement part in from Ali-E.
But i am going to try to check over other gates/drivers on all of these boards first.

Edit to add:
Took another look at this sustain and it looks like there are about 5 more P155E ICs on this board.
At least one is shorted across all pins while others look partially shorted. I am not sure what they are supposed to be but since I am ordering a 10 pack i'll have enough to replace all of them if need be.
I'll take a look at the other sustain for components that look dodgy as well.