no backlight supply volts hisense ub50ec591uwt

[giorgi711]

Re: no backlight supply volts hisense ub50ec591uwt

Scheme image has poor quality, see PDF file in attachments.

[giorgi711]

Re: no backlight supply volts hisense ub50ec591uwt

Can you please explain me, what does SW(BL_EN) abbreviation means? What is it for ?

In order to measure voltage on sw pin, I connected the black wire of multimeter to gnd pin(num. 1 on XP805 on image) and red wire to SW pin, after that one of capacitors(25V) swollen and blew smoke.

Before i did that, voltage between 12V pin and gnd was 24V, and between 16V and gnd was 32V.

Here is scheme of PSU of hisense tv.

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

finally fixed .
the led driver ic LX27901 ID was replaced ,
i had to get it from a supplier in Spain ,so sorry for the delay in this post ,
as you all know it seems to get harder with every job to source parts.
thanks all for your help ,
.ive learned not to trust what some customers say ,
as this tv clearly had been got at by some previous attempt to fix .(two leds had been replaced)
one of the foils feeding the panel had a slight tear in it add was damaged,
,(if you flexed it gently we had lines and noise in left hand side of pic) but i managed to replace it,after reducing the backlight settings from 100 to 25% still a good pic .thanks to all who took the time to help

[Diah]

Re: no backlight supply volts hisense ub50ec591uwt

parts ordered i will update asap

yours PSU working on almost the new standard circuit design by producing certain operation Voltage which converted VIA DC to DC step downer at MB, like other brands LG OLED / nano cells / U LED Panels.. which it need another method to run the PSU as stand alone.

So i think you and any other members whom don't have yet ...need to have DC to DC step downer PCB, they are cheap less than 3USD with wide range in and out V.. so you can exam yours PSU and BL circuit with out need the MB to narrow any future issue it may accuse by MB

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

parts ordered i will update asap

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

theres 11 strips with 6 leds on each ,but theres two strings, so each strip has 3 that link to next strip so 33 leds on each string
i stand corrected re the DM in diode test mode

[budm]

Re: no backlight supply volts hisense ub50ec591uwt

replacements:
oc when lit dimly
960 ohm in diode test with leads reversed
originals:
oc not lit (need a little more volts than DM supplies in diode test mode to light)
960 ohm with leads reversed.

the 8 ive replaced would all light up with DM but measured oc in reverse direction

Your meter when set to diode mode show the reading in Ohm?
Meter in diode mode test it will show the Vf of the junction in Volt not Ohm.
BTW, how many LED strips does this panel have and how many LED's per strip?

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

I am curious, what does your meter show when testing the working LED in diode mode in both directions?

replacements:
oc when lit dimly
960 ohm in diode test with leads reversed
originals:
oc not lit (need a little more volts than DM supplies in diode test mode to light)
960 ohm with leads reversed.

the 8 ive replaced would all light up with DM but measured oc in reverse direction

[budm]

Re: no backlight supply volts hisense ub50ec591uwt

I am curious, what does your meter show when testing the working LED in diode mode in both directions?

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

no
with your advice the leds were o/c
even though they would light up with battery
ill have a sort out in workshop too see what leds i have
and see if they are suitable ,thanks for your effort
i need now to have a rest

[Diah]

Re: no backlight supply volts hisense ub50ec591uwt

should i try to order 6v types with zener ?

this takes me back to start of post
this tv has two strings of leds each strip has 6 leds
3 are in one chain
and 3 are in the other chain on each strip .
so is it possible that the drive circuit "sees" a difference in the two strings and then shuts down the BL supply?
in total ive fixed about 60 tvs with backlight problems and usually managed a repair using salvaged leds from scrap tvs with broken screens or leds bought from china
i dont think ive had many with two strings of leds .
in the other repairs when the BL feed is removed you can usually measure voltage on the BL feed socket this is what is to me so unusual with this one

are you now uncertain that you found 8 LEDs open zener ?
usually voltage can be traced on LED socket for short time..if there issue at LED.. but remember you told here that you cant see any picture or info on the screen when you used torch light.. just sound you have.. it could be too MB don't turn on the BL and cut off picture.. we / i do make suggest on your comment and test..

show me all your scrap working strings label LOL we me find LEDs working for this set..

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

should i try to order 6v types with zener ?

this takes me back to start of post
this tv has two strings of leds each strip has 6 leds
3 are in one chain
and 3 are in the other chain on each strip .
so is it possible that the drive circuit "sees" a difference in the two strings and then shuts down the BL supply?
in total ive fixed about 60 tvs with backlight problems and usually managed a repair using salvaged leds from scrap tvs with broken screens or leds bought from china
i dont think ive had many with two strings of leds .
in the other repairs when the BL feed is removed you can usually measure voltage on the BL feed socket this is what is to me so unusual with this one

[Diah]

Re: no backlight supply volts hisense ub50ec591uwt

heres the pics ive sent pics but error occured will try again later heres the numbers off the original strips
50 hd500ud b01 11x6 3030c 3s1px2
1140066

the size 3030.. 6V

i made sure the ones i replaced had the same zener foreward current readings with DM in diode test mode and replaced any that were showing do reverse

LEDs for TV backlight choices never being with zener diode forward measurements with DM ......
because all kind of zener they will show same ( close range ) however the working voltage are different.. same as if you measure normal zener which limited 21V will test with DM same value for one which limted 5.1V.

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

pics

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

heres the pics ive sent pics but error occured will try again later heres the numbers off the original strips
50 hd500ud b01 11x6 3030c 3s1px2
1140066

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

i made sure the ones i replaced had the same zener foreward current readings with DM in diode test mode and replaced any that were showing do reverse reading pics to follow

[Diah]

Re: no backlight supply volts hisense ub50ec591uwt

thanks for not giving up ,
now its time for me to be confused ?
leds ive replaced have the same reverse resistance as the original ones BUT the replacement ones will light dim with test meter on diode check ,
whereas the original ones need a slightly higher voltage so wont light with my test meter but will light with 4.5v

LOL,

let forget your PSU.. for now.. because in general we could find one issue at TVs not 2 or more.. and you did found OPEN LEDs, but 8 pieces at once are so many..
do you want to say the replacement one was 3.v and the original could be more?
which type and size they are? could you show us.. the defect one and the replacement..
or by chance you got photo of the string label

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

thanks for not giving up ,
now its time for me to be confused ?
the 12v must be regulated because its 12v on or off load ie; in and out of sby.
the 16v with no load is 20v ,when you bring out of sby it drops a little to 19v
now i dont understand what you mean "disconnect the socket from psu side and just connect the 12v from psu to end skt of MB 12V?"
the voltage on the MB is the same

the leds ive replaced have the same reverse resistance as the original ones BUT the replacement ones will light dim with test meter on diode check ,
whereas the original ones need a slightly higher voltage so wont light with my test meter but will light with 4.5v

[Diah]

Re: no backlight supply volts hisense ub50ec591uwt

the start up sequence is that once the 12v is produced the MB then provides this voltage
thanks for trying to help me

you posted voltage reading https://www.badcaps.net/forum/attach...2&d=1596616541 16V=20 on STY...!!!
Okay, so if the PSU only connect to wall socket and the power switch on it produce only 12V. !! is that correct ?
in case yes..
disconnect the socket from PSU side and JUST connect the 12V from PSU to the end socket of MB 12V.. and then check the voltage on the MB socket 16V and other.

about the LED you replaced ... we don't know what kind replacement you did and what type are the original one !!

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

sorry i may have confused you
no i only have one board to repair
i compared the resistances with a scrap board that uses similar fets for backlight

the voltage on the STB pin comes from the MB and is not produced by the psu .the start up sequence is that once the 12v is produced the MB then provides this voltage
thanks for trying to help me