lg 32LC46 backlight inverter board fault

[jimbofz]

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

[jimbofz]

heres some pics

[dick_barton]

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?

[jimbofz]

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

[R_J]

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

[jimbofz]

Originally Posted by R_J

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

[dick_barton]

It may be worth checking the electrolytic capacitors around the OZ964 for increased ESR or capacitance value.

[jimbofz]

Originally Posted by dick_barton

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

[lotas]

Inverter circuit.

[jimbofz]

Originally Posted by lotas

Inverter circuit.

many thanks Lotas

[jimbofz]

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

[Biruslapio]

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?

[jimbofz]

Originally Posted by Biruslapio

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

[Biruslapio]

is the LCD darker or the lamps themselves? If the lamps + polarization sheets are ok then it's a t-con or panel problem.

[jimbofz]

Originally Posted by Biruslapio

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

[Biruslapio]

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.

[jimbofz]

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 ?

[jimbofz]

i will try again
spin them then upload again
nope that didnt work im confused?

[Biruslapio]

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.

[lotas]

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