no backlight supply volts hisense ub50ec591uwt

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

show us clear photo of the back side of the PWB

heres pics of print side psu in pic 3 you can see that the last 5 pins are not used

[Diah]

Re: no backlight supply volts hisense ub50ec591uwt

when you do 2 jumper 1K ... the second one between STB to PWM2 ( orange) how much the volts read on the orange pin after the 1K ?? and before on STB pin. and are you sure no V on BL socket ??( you can disconnect the LED socket and measure )

BTW: i think you have over clock on the hot area.. this why the 16V show 20 ... UD901 &902 need to test them after the free them from the boards

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

ud 901/902 check out ok by comparison with similar board using same fets
the psu pin STB has no volts on it until main board is plugged in so links with 1k resistors wont start

[Diah]

Re: no backlight supply volts hisense ub50ec591uwt

ud 901/902 check out ok by comparison with similar board using same fets
the psu pin STB has no volts on it until main board is plugged in so links with 1k resistors wont start

i am confused .. are you repairing now 2 power boards at same time ?? how it come STB voltage not exist only if MB connected ??? sorry man i cant follow your points.. it make real headage

[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

[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

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

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

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

[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

pics

[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

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

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

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

[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

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

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

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

[jimbofz]

Re: no backlight supply volts hisense ub50ec591uwt

parts ordered i will update asap