sony kdl 40x 3500 no backlights

[dick_barton]

You may have more than one CCFL on the brink of failing bearing in mind that they are all the same age.

[jimbofz]

Originally Posted by dick_barton

You may have more than one CCFL on the brink of failing bearing in mind that they are all the same age.

good point
thats somthing that had not occurred to me
thanks

[jimbofz]

reviving this thread as a strange fault has occured.
the original fault was one of the ccfl failing ,causing invertor error to shut down backlight .i removed one ccfl tx and fitted link across pin 1 and 4 ,thus removing the faulty ccfl from the cct

now for the strange bit ,
this has worked for weeks no problem ,
until the pic went off leaving sound and backlights still on
green led on .
when i switch to sby the led changes to red ,as you would expect but the sound and backlight remain on !
if you unplug mains and try again all is well for 5 minutes ,then the pic is lost ,with sound still on ,and b/l still on .
ive checked all supplies in fault condition ,all ok
cleaned lvds connections ,
to be clear the backlight stays on

[vinceroger69]

when the picture is lost do you still have voltage at the tcon fuse

[jimbofz]

ive removed the screening plates
but as youve guessed when powered on
fault not present ,ive tried heat and freeze ,no luck .
i will check t con volts as soon as fault occurs

whilst waiting ive been studying cct
the psu relay ,is not as straight foreward
as you might expect
,when powered off theres a final click a good few seconds after removing power also it has a 6.8 ohm ww across its contacts
which puzzles me ?
so when its open it still has 6.8 ohms in cct

[budm]

The 6.8 Ohm across the relay contact is for limiting inrush current when power is applies to the circuit, the relay is closed to bypass the resistor when TV is turned on.

[jimbofz]

Originally Posted by budm

The 6.8 Ohm across the relay contact is for limiting inrush current when power is applies to the circuit, the relay is closed to bypass the resistor when TV is turned on.

thanks .
perhaps you could explain where the" power on"
to psu comes from on this sony ? the main board is labelled AE board
on this i cant find power on from micro?
above this board is FB2 board
these two boards are connected together with multi pin connectors
ive studied the cct of both boards,with no luck
the sby volts is 5v from psu ,this is fine
theres a Pfc detect pin on the psu board, that goes high when psu runs
i just want to make sense of it

[nomoresonys]

One good thing about intermittent fault, you can check lots of voltages when it's working and compare them to when it's at fault, check all your solder joints look them over real close and give m the wiggle test, check all the voltage regulators on the mainboard and the test points on the tcon, hopefully you will find something.

[jimbofz]

Originally Posted by nomoresonys

One good thing about intermittent fault, you can check lots of voltages when it's working and compare them to when it's at fault, check all your solder joints look them over real close and give m the wiggle test, check all the voltage regulators on the mainboard and the test points on the tcon, hopefully you will find something.

thanks ,i may have made some progress ,
on the board above the main board marked FB2 (the one inside metal can)
you have to remove cam board and the AVC board
(tv will work without these 2 boards )

i could get fault to show itself when i heated it up with hairdrier and then with use of freezer spray .
so i removed board and found 3 100uf caps faulty with my esr meter .
ive replaced them and repeated the test with heat and freeze and tv remainds on.
the esr readings of the caps would change with heat
2 were on the print side of board and one on top
looks promissing ,
if it completes the repair i will post pics of the board
as theres no component ref numbers

[jimbofz]

well youve guessed it .
been fine running since my last post re changing caps
now it has decided to test my brain futher ,
i now get 5 blinks at switch on which is usually to do with t con
(theres two t con boards just to add to the mix!)
fuses on both tcons decided to fail ,no obvious shorts
so replaced fuses and still 5 blinks
12v supply on t con ok
and nothing getting hot
yes i did check all the earth screws in place
so im stumped
any thaughts ? (apart from scrap it )

[jimbofz]

looks like the end of the road for this one,at least i found the fault .
one of the four tcon foils is faulty
to remove both ends is major strip down ,
once done if i flexed gently the tv would trip to 5 blinks .
i removed the faulty foil and the contacts had lifted and were shorting .
trying to find a replacement is nigh on impossible ive kept some foils from scrap tvs but none are suitable

[nomoresonys]

haven't had to do it myself but have seen some have success by trimming a little off the end of the cables.

[jimbofz]

Originally Posted by nomoresonys

haven't had to do it myself but have seen some have success by trimming a little off the end of the cables.

yes tried that but all contacts lifted from plastic so when slid in they s/c ,
tried to s/glue with coctail stick and head up magnifier.
so annoying as these things probably cost peanuts to manufacture

[jimbofz]

well well well managed to find replacement foil ,
bingo rewarded with great pic.
it lasted 6 seconds ,
with scart i/p sound also cut out after 6 seconds now i get 5 blinks
removed logic board and t con tested all s mount caps with esr meter measured all vcc supplies for low resistance to deck all ok

i think the micro is entering protect mode
its nothing to do with backlight
ive studied cct ,but cant a find cct for the t con board in the manual
t con number:404652hcc 8lv1.8
it has 4 foils to connect to panel not the usual 2
i always like to repair to component level ,
just as well, as theres no cheap t con boards
i suppose what is bothering me the most is the picture is perfect
none of the usual symptoms you get with t con faults
on the logic board there was two 47 mf caps poor esr which i replaced

is there a way to force set on ,ie overide prot cct to allow me to enter s mode to clear the fault?
every time it will come on with good pic for 6 seconds
any help please

[nomoresonys]

Wonder if a firmware update would fix it, didn't see any on the sony UK site tho.

[jimbofz]

yes not avail from sony