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Old 12-19-2021, 06:58 AM   #1
jimbofz
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Default lg 32LC46 backlight inverter board fault

Hi this oldie had no backlight .after replacing caps on 24v rail ,
still no b/l this uses inverter type:1315 B1-16A,
im sure ive come across the same inverter in a samsung possibly le32r88bd ?
all t/x in board test ok ,so i fitted 15k and led to pin 4 of oz964gn ic
this allows protect to be temporary overridden.
b/l now comes on
but the left hand side of pic is gradually darker than the right side
i have the cct for the tv
but it does not have inverter cct.
i opened it up to inspect the ccfl tubes
and they dont have any black marks at the end
and the light produced is the same gradual light to dark,
in the past ive had individual ccfl s fail
but never had this shading effect
i suspect something on the earthy end of the ccfl s ,
possibly a component on the inverter board
can anyone help with a cct
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Old 12-19-2021, 10:44 AM   #2
jimbofz
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Default Re: lg 32LC46 backlight inverter board fault

heres some pics
Attached Images
File Type: jpg IMG_20211219_162732.jpg (455.5 KB, 9 views)
File Type: jpg IMG_20211219_162620.jpg (870.0 KB, 29 views)
File Type: jpg IMG_20211219_162647.jpg (652.5 KB, 11 views)
File Type: jpg IMG_20211219_162631.jpg (964.0 KB, 8 views)
File Type: jpg IMG_20211219_162554.jpg (924.3 KB, 8 views)
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Old 12-20-2021, 09:15 AM   #3
dick_barton
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Default Re: lg 32LC46 backlight inverter board fault

Have you checked the underside of the inverter board for hot spots ie browning of the board.

Is the PFC voltage measured as given in the manual?
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Last edited by dick_barton; 12-20-2021 at 09:22 AM..
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Old 12-20-2021, 10:25 AM   #4
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Default Re: lg 32LC46 backlight inverter board fault

yes the PCF is fine 380v
,and theres no sign of overheating on underside of pcb
.on the earthy end of the ccfl,s theres 2 fine connections to inverter board,
these go to diodes d15 ,d16 they check ok just wondered what they are for?
any ideas
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Old 12-20-2021, 11:06 AM   #5
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Default Re: lg 32LC46 backlight inverter board fault

are the 4 fuses on the inverter board ok? Check the secondary resistance of each transformer winding and compare them to see if one ore more has a different reading, I thing they should be around 600~900Ω

Last edited by R_J; 12-20-2021 at 11:10 AM..
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Old 12-20-2021, 12:55 PM   #6
jimbofz
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Default Re: lg 32LC46 backlight inverter board fault

Quote:
Originally Posted by R_J View Post
are the 4 fuses on the inverter board ok? Check the secondary resistance of each transformer winding and compare them to see if one ore more has a different reading, I thing they should be around 600~900Ω
all fuses ok and all tx windings measure same . which is good
when prot override b/l on
all tx run cool none are hotter than the others
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Old 12-20-2021, 01:05 PM   #7
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Default Re: lg 32LC46 backlight inverter board fault

It may be worth checking the electrolytic capacitors around the OZ964 for increased ESR or capacitance value.
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File Type: pdf oz964.pdf (318.7 KB, 3 views)

Last edited by dick_barton; 12-20-2021 at 01:08 PM..
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Old 12-20-2021, 01:16 PM   #8
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Default Re: lg 32LC46 backlight inverter board fault

Quote:
Originally Posted by dick_barton View Post
It may be worth checking the electrolytic capacitors around the OZ964 for increased ESR or capacitance value.
thanks ,there fine on my esr meter and cap meter
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Old 12-20-2021, 02:55 PM   #9
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Default Re: lg 32LC46 backlight inverter board fault

Inverter circuit.
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Old 12-20-2021, 04:21 PM   #10
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Default Re: lg 32LC46 backlight inverter board fault

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Originally Posted by lotas View Post
Inverter circuit.
many thanks Lotas
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Old 12-21-2021, 09:32 AM   #11
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Default Re: lg 32LC46 backlight inverter board fault

the voltage shown on cct for return end of ccfl,s is 1.8v this is only .2v
the 5v supplied via q2 is ok at 4,9v
pin 14 of u2 should be 4.4v its 3.7v
this goes to u3 pin 14 shown as dim
this is fed via 100k r50 which measures fine
any ideas please
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Old 12-21-2021, 10:09 AM   #12
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Default Re: lg 32LC46 backlight inverter board fault

Are the voltages across the fuses the same?
I undestood that there's a gradient effect in the CCFLs, from top to bottom or the opposite, is that it?
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Old 12-21-2021, 10:46 AM   #13
jimbofz
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Default Re: lg 32LC46 backlight inverter board fault

Quote:
Originally Posted by Biruslapio View Post
Are the voltages across the fuses the same?
I undestood that there's a gradient effect in the CCFLs, from top to bottom or the opposite, is that it?
all fuses 24v supply fine pic dark on left then gradual increase to perfect pic on right
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Old 12-21-2021, 11:00 AM   #14
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Default Re: lg 32LC46 backlight inverter board fault

is the LCD darker or the lamps themselves? If the lamps + polarization sheets are ok then it's a t-con or panel problem.
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Old 12-21-2021, 05:07 PM   #15
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Default Re: lg 32LC46 backlight inverter board fault

Quote:
Originally Posted by Biruslapio View Post
is the LCD darker or the lamps themselves? If the lamps + polarization sheets are ok then it's a t-con or panel problem.
thanks
i see where you are going with this
but i cant get inverter to start without overriding the protection, as posted earlier.this is why i was focusing on the inverter board
when i opened it up to examine ccfl,s they looked fine just darker at left side than the right ,
i did expect to see one that was out ,
causing prot to cut out b/l but no they were fine
i also checked the foils to see if they were causing the shading
but they all looked fine when i gently flexed them
if fault was t con or panel ,i dont think it would kill the b/l
would you agree?
its a head scratcher
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Old 12-21-2021, 09:01 PM   #16
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Default Re: lg 32LC46 backlight inverter board fault

Post a picture of the issue.

Are these lamps U shaped or do they end up fitting into at a long vertical metal on the opposite side of the chassi? If they are darker might be too low voltage, or bad connection in one of the sides.
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Old 12-22-2021, 03:50 AM   #17
jimbofz
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Default Re: lg 32LC46 backlight inverter board fault

yes i suspect low voltage.
the ccfl,s are not u shaped
all connections to each end of them were checked
the "earthy" end should have return voltage on cct shown as AA 1,8v
but its only .2v
here are some pics
i dont understand why pics are upside down ,i check their orientation before upload and they are correct ?
Attached Images
File Type: jpg IMG_20211222_092550.jpg (284.0 KB, 6 views)
File Type: jpg IMG_20211222_092639.jpg (301.5 KB, 5 views)
File Type: jpg IMG_20211222_092704.jpg (333.6 KB, 5 views)
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Old 12-22-2021, 03:58 AM   #18
jimbofz
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Default Re: lg 32LC46 backlight inverter board fault

i will try again
spin them then upload again
nope that didnt work im confused?
Attached Images
File Type: jpg IMG_20211222_092550.jpg (284.0 KB, 4 views)
File Type: jpg IMG_20211222_092639.jpg (301.5 KB, 5 views)
File Type: jpg IMG_20211222_092704.jpg (333.6 KB, 5 views)
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Old 12-22-2021, 09:22 AM   #19
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Default Re: lg 32LC46 backlight inverter board fault

That's probably the forum's auto resizer.

So you must have an inverter fault, there is no way all the lamps aged uniformly and got darker on one side.

What's the voltage on ERROR, ON/OFF, I-PWM and E-PWM?

One of these PWM voltages controls the lamp brightness, if this is the same as other old LG LCDs, 3.3V should be maximum brightness, and less than 0.8V it doesn't even turn on.

These wires that you used for bypassing the error pin, they're too long, try using the least amount of wire you can, if nothing changes, I suggest replacing the inverter board, it's cheap at least.
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Old 12-22-2021, 09:34 AM   #20
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Default Re: lg 32LC46 backlight inverter board fault

This inverter suffers from poor soldering of smd components (resistors, capacitors ...) try to solder the whole board well.
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