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

[DXseekerMO]

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

All these knowledgeable people in here and no one can tell me how to spec this fuse or direct me to a resource to do it myself?

[DXseekerMO]

Vizio D55-f2 backlight/power supply 20v/24v rail output high 26.5v

So I just got this model Vizio in yesterday with power/sound/image/no backlights. Here's the voltage readings from the Power Supply:

TV plugged in, off state
Pin1-0
Pin2-0
Pin3-0
Pin4-0
Pin5-0
Pin6-0
Pin7-10.06v
Pin8-10.06v
Pin9-10.06v
Pin10-10.06v
Pin11-0
Pin12-0
Pin13-0
Pin14-0
Pin15-0
Pin16-0

TV plugged in, on state

Pin1-26.5v
Pin2-26.5v
Pin3-26.5v
Pin4-0
Pin5-0
Pin6-0
Pin7-12.66v
Pin8-12.64v
Pin9-12.66v
Pin10-12.64v
Pin11-0
Pin12-0
Pin13-0
Pin14-0
Pin15-2.99v
Pin16-3.36v

In addition, upon the Main Board fuse 4501 is open and no voltage is present at the backlight connectors. The source voltage (26.5, 20/24 expected) is present on the voltage in side of the fuse.

The first thing I did was check for a short upon the output side of the fuse from the fuse itself to chassis ground. No short found, meter reads open.

Before I proceed, let me say this. If there were any evidence of even a small short on the output side of the fuse I WOULD HAVE NOT proceeded with the next step!

After finding no short on the output side of the fuse, I used a pair of tweezers to jump the fuse while the TV was in an on state. I expected an arc flash upon contact and did get one, but I think this flash was appropriate for the expected current in this circuit. When the fuse is jumpered the backlights turned on and I saw no evidence of anything in the LED drive circuit overheating. The truth is I didn't expect any since there was no short found on the output side of the fuse.

I'm thinking about ordering a couple fuses and installing one to see if it opens again, but I need to make sure I order the right size and rating of fuse.

As you can see in the picture it is either gray or white with the letter "Y" stamped upon it. Can anyone tell me what the size/rating is for this fuse and whether or not it's a fast or slow-blow type?

If not, can anyone direct me to a resource where I can look it up?

Thanks for your help folks.

[alfiedon]

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

Does anyone have the output voltages for CN6101 & CN6102 ?

[Nonya333]

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

also this seems like a main board issue

[Nonya333]

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

i would rather find the fault and increase my diagnostic experience

[Nonya333]

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

is it nornal for there be pisitive voltages on backlight negative pins amd if notnwhat causes this?

[nomoresonys]

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

These powerboards are priced cheap on ebay, that's the way I would go if I wanted to get it going quickly without tracking down the faulty part/s, just need to insure a match by matching the numbers on the white sticker: https://www.ebay.com/sch/i.html?_fro...acat=0&_sop=15

[dick_barton]

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

Can't be 100% certain but it looks like a 5A slow blow.
https://tinyurl.com/y3pchgd2

[Nonya333]

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

i understand but instill need to diagnose the cause of the blown fuse

[nomoresonys]

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

You have to use the same type fuse that came out, it matters if it's a fast blow or a slow blow also.

[Nonya333]

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

the fuse was blown prior to me touching anything. it was a white smd with the letter "Y". i also could not find info on that.

i found a bigger package smd fuse rated at 2a and replaced that. the set worked for approximately 5-10 hours and then fuse blew again

the 5r1 resistor was showing up as a capacitor on my cheap esr meter and showing higher resistance i believe. i still have it i will have to double check

[budm]

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

1) OK, i see the Fuse F4501 now.

2) When did the fuse blow?

3) Was the 5R1 resistor blown open circuit?

4) Need to see the pictures of the whole backside the TV showing how all the boards and the backlight LED's are connected together.

[Nonya333]

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

bad pu4501? i cannot find data sheet for this ic

[Nonya333]

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

what could cause the polarity to be reversed at cn6101?

[Nonya333]

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

and replaced a 5r1 that was bad with the bigger 5ohm smd

[Nonya333]

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

there is no smd fuse i just soldered a jumper wire

[budm]

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

top circled smd is the resitor i replaced. there is another 5r1 smd slightly lower.

the circle on right is where i put a jumper wire for the smd fuse. difficult to see it is a tiny piece of wire

The 5R1 resistor close by is part of the RC snubber network for the Diode PD45??.

I cannot see how you can have a SMD resistor and SMD fuse on just two solder pads, you are not making any senses to me.

[Nonya333]

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

top circled smd is the resitor i replaced. there is another 5r1 smd slightly lower.

the circle on right is where i put a jumper wire for the smd fuse. difficult to see it is a tiny piece of wire

[budm]

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

https://www.badcaps.net/forum/attach...9&d=1601919019
Is that Brown Green Silver Gold resistor you installed? That is 0.15 Ohms.
That is current sensing resistor connected to the Source pin of the MOSFET's PQ4501, 4502 so you cannot just put in any value resistor it's place.
Was the 5R1 resistor bad? What are the color band of the resistor?

Where is the wire for the fuse?

[Nonya333]

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

i tested leds with tester to led directly without pcbs and on cn6102 the voltage was higher but each line from connector to strip produced steady voltage on all strips

i did not remove panel to access strips because i am not that good at removing and reassembling lcd without damage