LG 60PZ750 running hot and maldischarged

[goldbird78]

Hi All, I have a 60PZ750 that I repaired the EBR73561701 Zsus board. Tv runs good for about 30 min to an hour then the picture looks maldischarged with red & green snow sparkles on lighter pictures, also I noticed the TV seems to run hotter that the usual plasma's. All my voltages seem good.

VS 201.2
VA 55.07
5V 5.13
VSC 150V
VZB 105.5

I have no history on this TV as I picked it up for cheap "not working". On the Szuz board I replaced the fuse, 6 FGPF4633 transistors and the 12 gate resistors. I have attached some pictures. Any help would be much appreciated. Tom if your out there I got myself a new digital scope

[Biruslapio]

Re: LG 60PZ750 running hot and maldischarged

There are SMD resistors and optocouplers who also can fail when IGBTs short,on solder side,check all optocouplers for low resistances between pins,and 10 or 100 OHMs resistors,ceramic capacitors.

[dick_barton]

Re: LG 60PZ750 running hot and maldischarged

I'm not 100% certain but shouldn't Vzb when measured between the two points = -178V as shown on the white label.

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Nice, show scope pics

Vzb should be ~110V
-Vy is -178V

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Are the SMD resistors the same as the gate resistors ? If so I did replace them if they are the two in parallel at the transistors. No idea what the optocouplers are as I am still a newbe in learning.

There are SMD resistors and optocouplers who also can fail when IGBTs short,on solder side,check all optocouplers for low resistances between pins,and 10 or 100 OHMs resistors,ceramic capacitors.

[dick_barton]

Re: LG 60PZ750 running hot and maldischarged

Thanks for the correction Tom.
Goldberg, what voltage do you read for -Vy?

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

I got an amazing deal....I think..Lol on a Siglent SDS1202X-E 2-Ch 200MHz Super Phosphor Oscilloscope. No idea on how to use it except for the basics. I will post a pic when I get back home on Sunday

Nice, show scope pics

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Don't know where would I find the test points ?

Thanks for the correction Tom.
Goldberg, what voltage do you read for -Vy?

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Siglent is decent and having the phosphor mode (like the Rigol DS1054Z) is really useful, so nice job.

-Vy and Vsc are on Y-sustain
Vzbias is on Z-sustain.

Points should be marked...look around for them.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Thanks Tom, below are my readings so far. I will hunt around for the
vy when i get home tomorrow.

VS 201.2
VA 55.07
5V 5.13
VSC 150V
VZBias 105.5

Siglent is decent and having the phosphor mode (like the Rigol DS1054Z) is really useful, so nice job.

-Vy and Vsc are on Y-sustain
Vzbias is on Z-sustain.

Points should be marked...look around for them.

[Biruslapio]

Re: LG 60PZ750 running hot and maldischarged

this is a repair that i did on a LG Z-SUS,the Y-SUS also had the same problem plus shorted IGBTs,the black 5 pin component is the optocoupler,it was shorted on the 3 pin side between colletor,base and emissor,10 OHM resistor was open and the ceramic cap was shorted,in your case they aren't otherwise the panel wouldn't light up,but an altered resistance can cause this.
Also you should first check all the voltages,bad -VY can surely cause this problem,it did red pixels on a TV i've repaired.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

I increased the VZB to 110v, all other readings were near perfect.

VS 201.2
VA 55.07
5V 5.13
VSC 150V
VZB 110.
Vy 178.1

Siglent is decent and having the phosphor mode (like the Rigol DS1054Z) is really useful, so nice job.

-Vy and Vsc are on Y-sustain
Vzbias is on Z-sustain.

Points should be marked...look around for them.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Just an update. I verified the problem still exists within the ZSUS board because I tested it in another TV and within 10 min it started to look maldischarged. Anyone have more ideas. I have attached pictures of the board. Could it be the driver IC's causing this ? Is it possible to use my new oscilloscope to track down the problem ?

I increased the VZB to 110v, all other readings were near perfect.

VS 201.2
VA 55.07
5V 5.13
VSC 150V
VZB 110.
Vy 178.1

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Yes it would be possible to use your scope.
You could follow the same guide as before with the VS_DA used to trigger your scope then one probe on the Z-sus output;
Since it's a digital scope you can then hit STOP and take a picture (may even save to USB for you)

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Is the Zsus output the resister by the VZB test points ?

Yes it would be possible to use your scope.
You could follow the same guide as before with the VS_DA used to trigger your scope then one probe on the Z-sus output;
Since it's a digital scope you can then hit STOP and take a picture (may even save to USB for you)

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Z-sus output is on those white connectors on the right. You can probably find it on a capacitor by tracing the big copper area that connects to those connectors. Don't mix it up with the ground, though.

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

how does this look ?

Z-sus output is on those white connectors on the right. You can probably find it on a capacitor by tracing the big copper area that connects to those connectors. Don't mix it up with the ground, though.

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Beauty!
And that's a nice waveform too, that scope renders that Z-sus waveform perfectly.
(Hmm...may have to consider a Siglent upgrade from my Rigol)

From that, I can see your Z-sus waveform looks perfect. Could you zoom in on the "burst" section on the right of the screen so you can see the sus_up and sus_down parts more closely? (This is the part of the waveform moving from 0-200V at a high frequency. It is responsible for making the panel light up.)

[goldbird78]

Re: LG 60PZ750 running hot and maldischarged

Thanks Tom......It is a weird one, when starting up cold the picture is perfect then as the TV warms up the screen gets maldischarged and it definitely the zsus board because when I swap it out into another TV the exact same thing happens. The attached scope and screen pictures are after the TV has been on for 20 min. It seems like a component on the board is overheating once the TV is on for 10-15 min.

Beauty!
And that's a nice waveform too, that scope renders that Z-sus waveform perfectly.
(Hmm...may have to consider a Siglent upgrade from my Rigol)

From that, I can see your Z-sus waveform looks perfect. Could you zoom in on the "burst" section on the right of the screen so you can see the sus_up and sus_down parts more closely? (This is the part of the waveform moving from 0-200V at a high frequency. It is responsible for making the panel light up.)

[tom66]

Re: LG 60PZ750 running hot and maldischarged

Yeah - looks odd

Can you try setting the panel on a fixed colour pattern so that the waveform doesn't change - you could use something like MS Paint

Then observe the waveform and see if anything happens to it as the fault develops - a video of the waveform may help me here