toshiba 65ul2163 dbl no backlights NOT BACKLIGHTS?

[jimbofz]

Hi this vestel 65in tv had classic no backlights ,so nothing new there!
tested with b/l tester and the b/l seemed to be fine
so investigated psu 17ips72 (on this 65inch there are 3 fets and control iv type DB83630P)
did a thorough check on b/l circuit all ok .
When i tried again with b/l tester all ok .but then when i reinstalled psu all worked fine ,
could there be a component on psu that is causing the protection mode to stop b/l
.maybee causing it to be too sensitive?
it seems to me if the b/l have been on with my tester ,within a couple of minutes if i reconnect the psu they will work fine

[EazyBone]

Backlights can be funky. I get tvs with BLs out from customers, turn on and they work. Even for 2-3 days and test fine. Doesn't always rule them out. They eventually go out again and I can then make them test bad. Just throwing that out there before you decide they are just good.

Pictures of PSU/connectors would help also

[jimbofz]

its still a work in progress
i have reduced the backlight current ,by increasing the fet source pin resistance
.it had 5 resistors in parallel .47 ohm
i simply removed two of these as an experiment .now the tv b/l come on as normal
i was given the tv so its fine to experiment

[lotas]

The 17IPS72 has a OB3363QP backlight driver, so the backlight current is regulated by 5 pin. ISET (when the resistance of this series resistor chain increases, the current to the LEDs drops).

[jimbofz]

thanks lotas and eazybone for your reply
.i will keep it running on test ,
the original owner had the b/l at 100%
reducing it to 50 % and removing two of the parallel resistors (increasing the resistance )
tv still gives good picture

[nomoresonys]

So what you have is probably one or more weak backlights, since lowering the current they stay on. It may live for a long time like that but if it does the same you know where to look.

[jimbofz]

exactly. i have replaced many b/l over the years
and sometimes its obvious that the strips have had a hard life as they are discolured
this one they all looked fine ,but only time will tell