Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

[Nonya333]

Re: Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

i also removed mosfet pq4804 because i am getting inconsistent reading than other mosfets and pq4807 reading slightliy lower resistance as well

[Nonya333]

Re: Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

please excuse the hackjob of the 15ohm resistor and wire for a fuse i could not find another 5R1 resistor.

when i plug in the connector cn6101 upside down with positive on neg side etc there is backlight and display is working however half does look brighter.

cn6101 is where polarity is reversed

[R_J]

Re: Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

How about posting some high quality, in focus pictures so we know what we are dealing with? It seems the led's are driven from the main board so I doubt the power supply is at fault, more likely you have an open led in the panel. If the power supply provides 24v and it reads 26v it is likely due to the fact the backlights are not working. If they were working the higher current draw would lower the voltage to 24v

[Nonya333]

Re: Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

there are 2 outputs to the led lights from the mainboard.

the one with less pins still shows half as positive and half as negative but the output is reversed

positive is showing up on negative and negative on positive

i poked around everywhere i am thinking it is the ic chip that controls mosfets

any help would be greatly appreciated

thanks

[Nonya333]

Re: Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

on the ps board on output there is a power mosfet to the 20/24v power rail/connector to main.

coming in from transformer there are 3 double schotky rectifiers.

there is a heat sink with bridge rectifier and what i am guessing is voltage regulator since i cannot see untill i desolder heat sink.

was your voltage regulator on hot side?

[Nonya333]

Re: Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

i will check it out. thank you for reply.

[dokma]

Re: Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

You can check my thread where I've managed to fix 19V spikes on a 5.3V rail. My issue was a faulty switching voltage regulator on the power supply. Perhaps your issue is something similar.

https://www.badcaps.net/forum/showthread.php?p=991809

[Nonya333]

Re: Vizio D55-f2 backlight/power supply 20v/24v rail output high 26v

is it normal for there to be aboit 26V on the 20v/24v power line and if not what would cause it to be so high?

[Nonya333]

no backlight on set.

the 20v rail fuse on the mainboard was blown. i replaced and backlight and tv worked for about a day before flickering and out again

input on mainboard for led should be 20v to fuse but is reading 26v at input and <3v output.

power supply output should be 20v/24v from connector and output is reading >25.6-26v

any suggestions?

i also tested backlights with tester and they were all same steady voltage and on

output switch transisters seem to be reading fine in circuit.

will check capacitors esr next