sony kdl 40x 3500 no backlights

[jimbofz]

this oldie works fine , good pic and sound for its age
but has intermittent backlights at switch on
led turns from red to green
when the fault is present there is sound via scart
ive replaced caps in psu which had poor esr readings and soldered up
then i soldered up the DF1 board above the psu ,i then removed the cover on the inverter board ,tested the small tx s and compared the resistances in case one was causing the backlight to shut off .
this model uses ccfl and inverter board.(sony call it ballancer board )
from the service manual the voltage on the pin marked inverter error reads 0volts ,it should be 3.1v .
the problem is most of the time it comes on as normal
when the fault is there all the secondary supplies from psu are good
has anyone had experience of these early models that you could share please
the inverter board is ssb400wa20s also used in some samsung models

[dick_barton]

There are a lot of lamps and they do start to fail as the set ages.

Can you plug in a usb stick with just a white jpeg picture and look carefully to see if you have any dimmer horizontal sections that would line up with the CCFL tubes. They tend to dim orange/yellow as they age.

If the fault is the inverter board then there's a cheap replacement from https://tinyurl.com/y4zsv2sl

Personally I would think that the tubes now 13 years old have aged and one or two are at the point of complete failure.

[jimbofz]

thats a bargain i will order it once ive completed diagnosis

im an old codger who likes to work to component level when possible.
ive tried it this morning and the fault is present
so im in with a chance .

i cant measure any small a/c volts on the i/p of any of the tx s on inverter board
according to a youtube vid i watched:
Troubleshooting LCD Backlight Failure Samsung LNT-4066 by norcal715 .

i should measure .2v ac on pin 2 of each tx
could it be a supply missing?
from df1 board (above the psu board )
what do you think?
by the way i tried to remove the inverter board from tv but its solid stuck ,
is this normal,do you have to prise them out ?

[dick_barton]

Have a good look at this video which could be useful to you
https://www.youtube.com/watch?v=oE6K4xBVweA

They are connected to 20 odd CCFL tube sockets so they tend to be very tight trying to remove them. I prise them out little by little first top then bottom then top then bottom, repeated and be very carefull not to lift them until clear of the CCFL sockets or the circuit board tabs that connect into the tube sockets will break.

[nomoresonys]

Maybe this other Norcal video will help: https://www.youtube.com/watch?v=8oZnSleucJ0

[nomoresonys]

""from the service manual the voltage on the pin marked inverter error reads 0volts ,it should be 3.1v ."" Maybe double check that, on many tvs you don't have a problem UNLESS voltage shows up on that pin.

[jimbofz]

Originally Posted by nomoresonys

""from the service manual the voltage on the pin marked inverter error reads 0volts ,it should be 3.1v ."" Maybe double check that, on many tvs you don't have a problem UNLESS voltage shows up on that pin.

when the tv was on working fine the 3.1v was present ,
when no b/l ov .
quote from manual:if theres an error in supply to ccfl ,pin 4 of cn6706
goes low. thanks for your help ,as i write this tv is in fault condition with 0v

[dick_barton]

i should measure .2v ac on pin 2 of each tx
could it be a supply missing?

Looking at the photo from shopjimmy it appears that it's pin No 3 of each transformer that connects the lamp error voltage to the diodes

[nomoresonys]

Ok, that one must go low, sure looks like an inverter issue then, did you try the testing from link in post #5?

[jimbofz]

yes the norcal video posts are very useful,
i definitely cant get any volts on inverter board tx s tried on a/c and dc with peak hold .
my stomach told me it was time for lunch, and ,yes youve guessed it ,when i returned it came on .
at least i was able to confirm that the cathodes of the diodes all have 2v on them (lamp error voltage)
so :when working ballancer error 0v
the invertor error 3.1v
the backlight on 3.2v
i also switched to another i/p with no signal, turned brill to max , and had a good look at display ,theres no dark horizontal stripe

[jimbofz]

i have removed the inverter board ,and its clear one of the tx has been under stress as the board is discoloured see pic
its the 4th one along marked with arrow in pic .
im going to remove it and link it out just for test purposes ,
to see if the fault clears .
although im not totally convinced ,because when the fault is present theres no volts at all on the primary side of the tx s

i suspect the ccfl its connected to, is drawing more current than the rest.
the tx measures exactly the same as the others.
sorry about the shadow on the pics

[nomoresonys]

Maybe check D117, see how it compares to the others.

[budm]

Just FYI:
https://www.badcaps.net/forum/attach...9&d=1610795611
This is Inverter board which produces High Voltage and feeds the Balancer Board which the lamps are connected to..

https://www.badcaps.net/forum/attach...0&d=1610819201
What are the Voltages on
VCC (DCV)
FB (ACV, in mVAC range)
OLP (DCV)
LD (DCV)

You also should try setting the backlights level (Not Brightness) down to 50% to see what will happen.

[jimbofz]

will post voltages ,
but at the moment tv is ok i will try it again later

[jimbofz]

Originally Posted by nomoresonys

Maybe check D117, see how it compares to the others.

d117 tested good ,same as all the other diodes on each pair of tx s

[budm]

You also should try setting the backlights level (Not Brightness) down to 50% to see what will happen.

[jimbofz]

Originally Posted by budm

Just FYI:
https://www.badcaps.net/forum/attach...9&d=1610795611
This is Inverter board which produces High Voltage and feeds the Balancer Board which the lamps are connected to..

https://www.badcaps.net/forum/attach...0&d=1610819201
What are the Voltages on
VCC (DCV)
FB (ACV, in mVAC range)
OLP (DCV)
LD (DCV)

You also should try setting the backlights level (Not Brightness) down to 50% to see what will happen.

here are the voltages when b/l is off:
VCC 12VDC
FB 0V A/C OR D/C
LD 12V
OLP ?cant find a reference to this is it over level protection?
inverter error .004v
ballancer error 0v
these voltages were taken with fault present .
i set the b/l to 50%.
i then removed the tx that was causing the ballancer board to be discoloured
i linked out pin 1 and 4 and it has not yet failed to start up YET
i keep trying it every 4 hours ,i intend to refit the tx and see if fault returns
i will post results thanks

[jimbofz]

fault returned
OLP volts on balancer board 0v

[budm]

Service manual for
SONY KDL-40X3500 KDL-46X3500 KDL-52X3500 CHASSIS FIX2

And Backlight topology.
According to the service manual, the OLP pin is not used.

https://www.badcaps.net/forum/attach...9&d=1610795611
Is the section of the DF1 board where the CN6708 is has dark marking due to heat or that is the shadow?

[jimbofz]

the panel pic sadly was just a shadow . see aditional pics ,
ive left the link on for the time being .
thanks for the manuals .
a strange thing this morning ,
although the tv came on as if there was no problem,
when i used the sby button on TV the pic and sound went off but i still had a feint raster ,ie the backlight stayed on .when faultfinding for no backlight i always use a scart i/p so i can confirm sound is present .it saves confusion .so the sound went off as did the pic info .

when following the flowchart for backlight faultfinding , (i know they can sometimes lead you up the garden path)
if 3.3v missing at cn6153 pin 3 suspect au board (main board)
perhaps i should turn my attention to the main board ? any thaughts please