VIZIO M3D550SR sound and faint picture

[hellride]

Recently picked up this Vizio M3D550SR for free and figured I'd have a go at trying to get it working. The problem is, this TV has me a little confused. The Vizio light on the front is on, the TV output's sound and when a flashlight is held to the screen, you can see that the lcd is working, but for some reason the LED's aren't turning on.

So I starting checking voltage's going from the power supply to the LED driver board, these are the voltages I got:

24v-23.6v
24v-23.6v
24v-23.6v
24v-23.6v
24v-23.6v
GND
GND
GND
GND
GND
on/off-3.2v
DIM-no voltage

All of those readings seem to be within the range shown on the power supply. So I checked the voltage going from the power supply to the mainboard, this is what I got:

on/off-3.2v
DIM-no voltage
12v-11.7v
12v-11.7v
GND
GND
GND
24v-23.3v
24v-23.3v
PS-ON-1.7v
5v-5v
5v-5v
GND

Again all those seem to be near the range shown on the power supply. Since the power supply is putting out the correct voltage for both the LED driver and the mainboard, I'm guessing I can rule that out? And since the mainboard is putting out sound and a faint picture, is it possible I can rule that out as well?

Another set of voltages I tested were those coming out of the LED driver. The LED driver was showing voltage going out, but since there is nothing printed on the board, I don't have a reference for what these voltages should be. I can post the voltages I got out of it if someone here knows what the voltage coming out of the LED driver is suppose to be.

Sorry about the long post, just wanted to be thorough. Any help on this would be appreciated.

Forgot to add, those voltages are with the TV on.

[budm]

Re: VIZIO M3D550SR sound and faint picture

Start with this:
https://www.badcaps.net/forum/showthread.php?t=39740
It looks like all the Voltages and signals are there with an exception of the Dimm control line.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

Couldn't find the edit button in my original post to post these. Battery died on my camera, so I wasn't able to get a picture of the LED driver board and the T-CON board, I'll post those when the camera charges. Sorry if the quality isn't great, not the best with camera's. If better pictures or something specific is needed, I'll try to get it.

Also want to correct a mistake on my original post. The DIM going to the mainboard is reading 5.1v. I get no voltage on the DIM going from the power supply to the led driver.

[budm]

Re: VIZIO M3D550SR sound and faint picture

The LED driver board is also controlled by the T-CON to give you that fake high contrast ratio spec.
Try disconnecting that small flat ribbon cable between the LED driver board and the T-con board to see what happen.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

Disconnected the ribbon cable going from the T-CON to the LED driver board, no change. Still get sound and with a flashlight held to the screen, you can see a picture, but the backlight isn't turning on.

I want to say the LED driver board is the problem, but testing the connector's at the top of the LED board, it is showing voltage going out to the LED.'s Though I'm unsure of what the correct voltage for those connectors is suppose to be. Here is the voltage readings I got out of the led board top connectors:

Left connector
pin1-50.2v
pin2-11.3v
pin3-8v
pin4-9.1v
pin5-8.1v
pin6-8v
pin7-8.1v
pin8-9.3v
pin9-8.4v
pin10-50.2v

Right connector

pin1-50.1v
pin2-8.7v
pin3-8.1v
pin4-8.4v
pin5-8.6v
pin6-7.8v
pin7-8.3v
pin8-7.8v
pin9-9.2v
pin10-50.1v

No idea if any of those voltages are off or not. Hoping someone here can someone here can tell me if they see something off with those number's.

[budm]

Re: VIZIO M3D550SR sound and faint picture

Please upload good clear pictures of the LED driver top and bottom sides without the shield.
I need you to check the DCV on the Voltage boost converter filter caps for the LED stings.
Any labeling of the pins on those connectors to the LED strings?

[hellride]

Re: VIZIO M3D550SR sound and faint picture

After taking the shield off, I did find label's for the left and right connectors, which is shown in one picture. Left filter cap read 50.2v and the right read 50.1v.

[budm]

Re: VIZIO M3D550SR sound and faint picture

It looks like it has two boost converter circuits, L102, Q101, D101 and L202, Q201, D201.
Both are producing the same Voltages, you may have to measure each cap one at at time to see if it does jump up higher than 50V and then settle down to 50V or not.
If the LED string has open LED, the output will jump up real high and then the protection circuit will kick in.
Then also take the reading without the LEC connectors in place to see if the Voltage also jumps up and then settle down to 50V or not.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

Tested both filter caps when turning the TV on. The left filter cap jumped up to 71.2v and slowly dropped down to 50.2v. The right cap jumped to 71.1v and slowly dropped down to 50.1v

Disconnected the connector's and tested again. Left cap jumped to 74.2v and slowly dropped to 50.2v. Right cap jumped to 74.1v and slowly dropped to 50.1v.

[budm]

Re: VIZIO M3D550SR sound and faint picture

OK, that's sound like the LED has open connections or open circuits due to bad LED.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

I was afraid of that. I suspected it could possibly be bad LED's, so I started stripping the TV down to the panel earlier to see if I could find any damaged one's. I got as far as pulling the metal frame around the panel off and lost my nerve to go any further after that.

Having stripped down lcd's on laptop's and small monitor's in the past, it's a pain to keep dust and finger prints out of the many layer's of the lcd. That and this lcd panel being pretty fragile, I didn't want to go any further.

Looking around for part's for this TV, I haven't seen any LED string's posted anywhere. I'm guessing these are pretty hard to get a hold of?

[budm]

Re: VIZIO M3D550SR sound and faint picture

LED strips are hard to come by, I do not have much fate in LED backlights after see so many of them failed in the BADCAPS forum.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

That's what I figured. The TV was free so, it was worth a shot at trying to get it going. I appreciate all the help we've given me.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

So since this TV is just sitting around, I figured I'd experiment on it. The worst I could do was damage something in a TV that is pretty useless in it's current state.

So I wanted to see if I could get any response from the LEDs with the mainboard disconnected. So, I disconnected the mainboard and applied 5v to the PS-ON pin. The original voltage reading I got from this pin was 1.7v, so when I applied the 5v to it, i fully expected something to pop. To my surprise, it didn't pop.

I than applied 3v to the ON/OFF cable going from the power supply to the LED driver. To my surprise, the LED's lit up!! Though they weren't exact working as intended. Instead of staying lit, they were flashing on and off every 2 sec's or so. The voltage readings I was getting from the LED driver when the backlight was flashing was pretty erratic, voltage spiking to about 76v when the LED's light up. I was either applying to much voltage to the pin's I jumpered or not enough voltage and/or current.

Since the LEDs did light up, wouldn't that rule them out as being bad? Since I did get a response out of the LEDs with the mainboard disconnected, would that indicate that the problem is with the mainboard?

Just wanted to get some advice here before i do anything else.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

Well, just figured I'd report back and say I got the TV working!!

budm, thinking about what you said about the DIM voltage not being present, I tested it again using a lower setting on my DMM. It was showing voltage, only 0.19v though which still seemed way to low to me. So just for the sake of experimenting, I disconnected the DIM line going to the LED driver, plugged the TV in, pressed the power button, and it powered right up!!

Question is though, would this be a power supply or mainboard problem? And would it be safe to just run the TV with the DIM line disconnected?

[Peter Chiu]

Re: VIZIO M3D550SR sound and faint picture

If I remember, I did fix one of those by change ( LG 6917L-0043A (KLS-E550RNP16 A) LED Driver)board.
would u please test Q201 and Q101 see if shooted?

[budm]

Re: VIZIO M3D550SR sound and faint picture

Dim control line is just for adjusting how bright the LED backlights will be, I usually run my backights brightness at 80%.
I do not know if your dim control line is PWM (10% pulse width = min brightness, 90% = Max) or analog 0~5V type.
Dim disconnect will probably drive the LED at max brightness.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

I tried a replacement LED driver board in it a few days ago, it wasn't the problem. The board was relatively cheap, so it wasn't a huge gamble.

After my previous post, I started checking all the HDMI port's on the TV. HDMI 1 and 2 get no signal at all, 3 and 4 work though. Talking to the previous owner, he said Directv had to come out and replace all his HD boxes because of a close call with a lightning strike. Having fixed a few TV's under similar circumstances before, the power surge likely traveled from the HD box through the HDMI ports that were hooked up at the time and damaged the mainboard.

So the mainboard will have to be repaired or replaced (expensive to replace on this TV). Though I'm not sure if the power supply has a problem with it or not.

[budm]

Re: VIZIO M3D550SR sound and faint picture

"alking to the previous owner, he said Directv had to come out and replace all his HD boxes because of a close call with a lightning strike." That is very important info.

[hellride]

Re: VIZIO M3D550SR sound and faint picture

"alking to the previous owner, he said Directv had to come out and replace all his HD boxes because of a close call with a lightning strike." That is very important info.

Yeah, sorry about that.

My dad works for Directv, so he got the TV from the original owner and gave it to me. My dad went to the owner's house for a DVR upgrade, not a service call, so the lightning strike must have happened month's ago. Original owner didn't tell him anything about it, just to take it or it was going in the trash.

Didn't get the original owner's phone number till yesterday. Called him and he told me what had happened.