Vizio M492i-B2 Won't Turn On

[John90]

Hi all,
My girlfriends grandpa asked me to take a look at his TV because it wouldn't turn on anymore. The TV is a Vizio Razor 49" model M492i-B2. I took the back off to access the circuit boards inside so I could inspect them for any obvious signs of damage but I couldn't see anything that really stuck out to me. I took a picture of each board so maybe someone might see something I didn't. The TV doesn't turn on and there is no stand by light or anything. Any help is greatly appreciated!

[budm]

Re: Vizio M492i-B2 Won't Turn On

What kind of tools do you have? We need to test the fuses and some Voltages testing.

[John90]

Re: Vizio M492i-B2 Won't Turn On

I do have a multimeter. If there's anything else I need let me know.

[CapLeaker]

Re: Vizio M492i-B2 Won't Turn On

So either you got no STBY voltage from the PSU or the main board is bad. All fuses on the PSU are good? When you plug the TV in you get roughly 170V DC on the main filter cap?
check if you have STBY voltage coming from the PSU going to the main board first.

[John90]

Re: Vizio M492i-B2 Won't Turn On

Thank you for your reply CapLeaker. The fuse(s) seem to be good. I checked the STBY voltage at the connection on the power board and the main board and I am getting 5v at both connection points. I checked the filter cap as well and I'm getting 170V DC from that as well. What should I check next? Your help is really appreciated!

[dick_barton]

Re: Vizio M492i-B2 Won't Turn On

Can you list the pin names and the voltages on them when out of standby.

[CapLeaker]

Re: Vizio M492i-B2 Won't Turn On

O.k. so far, you got STBY voltage and that is going to the main board.
Next you follow dick barton's post above. Do that with the TV off and on.

A problem is that this TV actually has a separate LED driver board and there are no pinouts that I could find, to see what pin does what. I doubt that if you disconnect the main board (and maybe the LED driver board too), while jumping PSon with a 1k resistor to STBY voltage, that the backlights come on. This is me hoping that the PSU has a pull up resistor.

I just got looking and SJ has sells all the boards as a repair kit for $75. For now I'd like to see the backlights first.

[John90]

Re: Vizio M492i-B2 Won't Turn On

If this isn't what you were looking for just let me know.

With the power cord plugged in these are the voltage readings I get for each pin on that connector.
NC-1
NC-1
NC-1
Blank-11.8
Blank-11.8
GRD-.8
GRD-.8
Blank-11.8
Blank-11.8
GRD-.8
GRD-.8
PS-ON-2.99
AC_OFF_DET-3.3
5VSB-4.99
5VSB-4.99

[CapLeaker]

Re: Vizio M492i-B2 Won't Turn On

When the TV is on like that, can you shine a flashlight into the screen to see if you can see a picture? Do the backlights flash on for a second when you turn on the TV?

The PSU looks fine, the main board is returning PSon, and the PSU turns on. So either there is still a other fault with the main board, or there is something wrong with that LED driver board or the backlights themselves. Could you measure the pins on CN202? I know there isn't any labeling, but there should be some power going form the PSU to the LED driver board.

[budm]

Re: Vizio M492i-B2 Won't Turn On

Check the DCV both ends of 0 Ohm resistor R9008, 9010 with ref..to chassis GND.
That LED driver board has two Boost converter circuits.
Vizio 75.50070.200 LED Driver.
http://www.shopjimmy.com/vizio-75-50...ed-driver.htm#
Pictures provided by shopjimmy.

[John90]

Re: Vizio M492i-B2 Won't Turn On

Budm, I checked R9008 and 9010 and get 24.70v on both.

CapLeaker, I was able to check the top pins on CN202, the pins on bottom are kind of hard to get too. The pins on top show 24.7v at the power board and the LED driver board. The bottom pins I could check showed 0v, I am guessing these are ground. The backlights don't seem to do anything at all when you try to power on the TV.

[budm]

Re: Vizio M492i-B2 Won't Turn On

This is going to be tough because we do not know the signal pins on the CN901.
If the board is getting the BL-ON then the DCV on Capacitors TC903, TC901 should jump up much higher than 24VDC.

[John90]

Re: Vizio M492i-B2 Won't Turn On

The 24VDC was on R9008 and 9010.
The voltage I am getting on capacitors TC903 and TC901 is
TC901=8.84VDC
TC903=12.54VDC

[dick_barton]

Re: Vizio M492i-B2 Won't Turn On

There's one selling quite cheap @ $14


http://www.ebay.com/itm/VIZIO-LAKERS...-/381520240952

[CapLeaker]

Re: Vizio M492i-B2 Won't Turn On

Those caps are only rated for 25V. If the get more voltage than that, they are gonna puke. However TC901 is low compared to TC903. Now here is a clue.

[John90]

Re: Vizio M492i-B2 Won't Turn On

With TC901 being low is there something else I should check next? Should I get a new board? Replace TC901?

[budm]

Re: Vizio M492i-B2 Won't Turn On

My mistake, I trace out those two sections with L902, L904, the power MOSFETs, the diodes: it is setup as a buck converter not boost converters, so the output should be <24V.
Need to get the spec of that U900, 904 to find out what the output Voltage should be based on the values of the feedback resistor network.
Also need to P/N of U902, 903.
Also need the pictures of the backside of the TV so we can see how all the boards are connected together.

[CapLeaker]

Re: Vizio M492i-B2 Won't Turn On

This led driver board is a pain in the rear, not having anything marked on the pins.
There must be a ribbon cable going from the main board to that LED driver board. One of these wires must carry the backlight on off voltage. Could you verify this that the main board is putting out the BLon? You would be looking at a 3v signal that appears when the tv is turned on and disappears with the tv off, same as the PSon signal.

Making a mistake is a human thing, I am not perfect either budm. What counts is the will to learn.

[John90]

Re: Vizio M492i-B2 Won't Turn On

Having a little trouble trying to find the BL-ON as nothing is labeled on these boards. I did find a pin coming from the main board that had 3V on it but the voltage never changed when I pressed the power button.

Budm, I got a picture of the wiring.

[budm]

Re: Vizio M492i-B2 Won't Turn On

CN901 should be the controller connector which goes to the main board, but as you indicated, they are not labeled, so all you can do is to take the DCV reading when TV is OFF and when TV is turned on.