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Old 07-06-2019, 08:32 AM   #1
angelos
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Default LG 42" Plasma Model 42PG20R-AFB (No picture)

HI guys,
I have another beast of a TV and lack the knowledge to fault find which board to look at.
When starting this TV you hear a click and Vs and Va come up as per plasma label but there is no pre-charge and no picture. As a matter of fact the Y-SUS and Z SUS boards are not getting the slightest heat on the heat sinks meaning they are not being driven at all.
The led on front panel shows TV is in the on state and when I press vol+ or Vol- the standby light flickers indicating that the main is at some extent operating.
At this point i can suspect any board especially the logic control board which has only one green light with the other two being off or perhaps something wrong with the main board.
Unlike the Samsung where you can short out two pins on the control board and force the controller to generate a test pattern to the plasma boards on the LG i know nothing like that.
Any fault finding tips would be greatly appreciated.

Regards
Angelos
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Old 07-06-2019, 08:39 AM   #2
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

A photo of the logic board, there are usually a couple of holes that are bridged for the test pattern.
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Old 07-06-2019, 04:09 PM   #3
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Ok will upload when able to. Thanks..
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Old 07-07-2019, 01:25 PM   #4
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Quote:
Originally Posted by angelos View Post
Ok will upload when able to. Thanks..
Clear focused close-up shots.
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Old 07-10-2019, 04:02 AM   #5
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Here are the picture of both sides of the logic board as discussed.
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File Type: jpg 20190710_115259.jpg (770.3 KB, 9 views)
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Old 07-10-2019, 04:10 AM   #6
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Just to the right of the sticker, EXT_AUTO_GEN.
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Old 07-10-2019, 11:47 AM   #7
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Great. I will bridge the two pins and see what happens...
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Old 07-10-2019, 11:50 AM   #8
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

You also have to unplug the ribbon cable from the mainboard to the logic control board.
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Old 07-11-2019, 03:27 AM   #9
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Will do...
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Old 07-13-2019, 06:40 AM   #10
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Ok, i shorted the auto gen pins and removed the LVDS cable to the logic board. Switched on set and nothing still no panel drive.
Where do i go from here? I measure no shorts on Vs, Va etc. Those mosfets i tested all had no shorts on their pins.
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Old 07-13-2019, 07:08 AM   #11
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

You will have to test the igbt's in diode mode. Removing them is best when testing.
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Old 07-13-2019, 02:41 PM   #12
angelos
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Have you had an igbt go open circuit? How do we test those since some transistors do not get triggered by the small voltage the multi metet produces or am i wrong?
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Old 07-13-2019, 04:36 PM   #13
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Default Re: LG 42" Plasma Model 42PG20R-AFB (No picture)

Yes, I have. I have a cheap transistor tester that I use, after testing with my DMM. See pics.

Sometimes original bad igbt's read like this too.
Attached Images
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File Type: jpg 2016-11-30 05.18.25.jpg (2.54 MB, 5 views)
File Type: jpg 2016-11-30 05.15.30.jpg (2.74 MB, 4 views)

Last edited by tvtimmy; 07-13-2019 at 04:38 PM.. Reason: Explanation
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