Vizio VO420E - INV_ON signal stays low

[ngth82]

Good afternoon all -

I have another TV in hand. This time it's a Vizio VO420E. I picked it up for free the other day. The TV is manufactured in the 2008/2009 time frame.

Pictures of the boards and an overall view are attached. I checked the voltages on the power board.

Initial assessment
- There is some sign of life on the main board, but without schematics, i see that a few caps have 0V on either side, and a couple of LDO's and switching supplies have output voltages. I just don't know if the values are correct.
- The backlight does not turn on
- no sign of life with flash light test shining at screen
- The optical audio out does not illuminate red.
- The main board fuses near the power connector are okay -
-- F1 - 5.128V on both sides
-- F2 - 12.28V on both sides

Main caps
+165V across the main caps when off
+392V across the main caps when the power button is pushed.
The voltage across the main caps stay steady.

Power Supply - Connector CN201
Pin name, actual voltage read
ON/OFF, 0V (when off), 3.166V (when on)
+12, 12.27V
+12, 12.27V
+12, 12.27V
GND, 0V
GND, 0V
GND, 0V
GND, 0V
GND, 0V
ST/+5V, 5.194V
ST/+5V, 5.194V
ST/+5V, 5.194V

Power Supply - Connector CN202
Pin name, actual voltage read
DIM, 0V
INV_ON, 0V
VBR_A, 0V
No Connect
Status, 0V
No connect

Tests
- I was able to force the backlight on by removing the cable from connector CN202, and hooking up an external power supply to the INV_ON signal when the TV is ON.
- The backlights glow - at least the back lights work.
- I disconnected the ribbon cables between the main board and the integrated T-CON, no change in behavior.
- It appears that the main board is not running yet.


Request
- Does anyone have the schematics for the main board or the service manual for this TV? I was not able to find it online. I was only able to find the following brief service manual in online form only:

https://www.manualslib.com/manual/10...page=19#manual

[attainteddragon]

Re: Vizio VO420E - INV_ON signal stays low

you main board is only half working. ps/on is present, but bl/on is missing.

a schematic is normally impossible to find foe main boards unfortunately.

you can try and trace the bl/on pin backwards from the connector and hopefully find the bad component, but mains are hard to find faults on.

have you checked all of your ldo regulators?

[budm]

Re: Vizio VO420E - INV_ON signal stays low

http://www.shopjimmy.com/catalogsearch/result/?q=VO420E

Look at EEPROM and Repair kit to see if it will fix your symptom.

[ngth82]

Re: Vizio VO420E - INV_ON signal stays low

Hey guys -

Thanks for the reply. I've been busy at work and didn't realize there were replies to the thread!

@budm - I'm going to cave in and give it a try. Looks like eBay has a kit that includes the EEPROM + 5 LDOs. for $15 including shipping.

@attainteddragon - Yes, here are the LDO voltages that I have found along with the markings on the package:

Pin orientations are looked at from "left-to-right" with the tab "up"/"north". I can't find a datasheet for the part marked L243 / G1117.

U11 - 7805CT
Pin 1 - 12V
Pin 2 - 0V
Pin 3 - 5V
Tab - 0V

U4 - L243 G1117
Pin 1 - 5.162V
Pin 2 - 3.29V
Pin 3 - 2.046V
Tab - 3.3V

U7 - 1084
Pin 1 - 2.065
Pin 2 - N/C, short pin
Pin 3 - 5.147
Tab - 3.3V

U9 - L243 G1117
Pin 1 - 1.259V
Pin 2 - 2.506V
Pin 3 - 5.142V
Tab - 2.506V

U8 - L243 G1117 - I think this one looks suspect.
Pin 1 - 0V
Pin 2 - 1.250V
Pin 3 - 3.3V
Tab - 1.250V

U2 - L243 G1117
Pin 1 - 2.045V
Pin 2 - 3.288V
Pin 3 - 5.137V
Tab - 3.288V

U4 - L243 G1117
Pin 1 - 1.372V
Pin 2 - 2.619V
Pin 3 - 5.140V
Tab - 2.619V

TU31 - I think it says EH13A / 925N05 - no voltage
Pin 1 - 0V
Pin 2 - 0V
Pin 3 - 0V
Tab - 0V

U21 - 4953 is what i can make out.
Looks like a dual channel P-FET like a Vishay Si4953
Pins 1 and 3 are the source
Pins 2 and 4 are the gate
Pins 5-8 are the drain.

Pin 1 - 12.25V
Pin 2 - 11.97V
Pin 3 - 12.25V
Pin 4 - 11.97V
Pin 5 - 0V
Pin 6 - 0V
Pin 7 - 0V
Pin 8 - 0V


U1 - 4953 is what i can make out.
Looks like a dual channel P-FET like a Vishay Si4953
Pins 1 and 3 are the source
Pins 2 and 4 are the gate
Pins 5-8 are the drain.

Pin 1 - 5.163V
Pin 2 - 0V
Pin 3 - 5.163V
Pin 4 - 0V
Pin 5 - 5.147V
Pin 6 - 5.147V
Pin 7 - 5.147V
Pin 8 - 5.147V

[ngth82]

Re: Vizio VO420E - INV_ON signal stays low

I found a separate thread that was talking about several components on the input:

- Ferrite bead L16 - 1 ohm across it. 1.18V both sides
- fuse TF1 (the "N" fuse) - that fuse is okay , it reads 0.6 Ohm, 0V both sides
- Ferrite bead L57 - 1 ohm across it - 0V both sides

Note that the drain of U21 is connected to L57, then to TF1. In the current state, it makes sense why it's 0V.
No dead short to ground on either side of the L16, TF1 or the L57 components.

[budm]

Re: Vizio VO420E - INV_ON signal stays low

U21 is probably not being turned on by the micro controller, it is probably use for supplying the switched 12V to run the T-CON board.

[ngth82]

Re: Vizio VO420E - INV_ON signal stays low

True. I'll continue to look around the board when i get a chance.
I attached an up close photo of the power input area with the two FETs.

I'm a little rusty on my P-FET logic. The pin out of U21 () has the Source on Pins 1 & 3, the Gate on pins 2 & 4, and the drain on pins 5-8.

The Gate should be controlled by the microcontroller. I haven't followed the traces for the Gate back to where they originate, but i would imagine that the source and gate should be both 12V.

If anything, if the Gate is "high" i should see a voltage expressed on the drain side and it should be close to the Source side, correct?

[budm]

Re: Vizio VO420E - INV_ON signal stays low

This is P-CH so the GATE Voltage will have to be at least 3~4VDC < than the Source pin Voltage for this P-CH MOSFET to be on.
I would not worrying about this MOSFET right since you have multiple command signal problems.
As you can see why the MOSFETs are OFF right now:

S: Pin 1 - 12.25V
G: Pin 2 - 11.97V
S: Pin 3 - 12.25V
G: Pin 4 - 11.97V
D: Pin 5 - 0V
D; Pin 6 - 0V
D: Pin 7 - 0V
D: Pin 8 - 0V

[vinceroger69]

Re: Vizio VO420E - INV_ON signal stays low

i would probably try the eeprom repair too if this was my set as they do seem to fail a lot on vizio

[R_J]

Re: Vizio VO420E - INV_ON signal stays low

Sometimes if you freeze the eprom/flash the tv might work, freeze the ic before pluging in the tv as it usually gets read when first pluged in. then see if it will turn on.

[ngth82]

Re: Vizio VO420E - INV_ON signal stays low

Hi R_J -

I tried freezing the EEPROM on the back of the board several times then plugged the unit in. Each time i waited until the main caps were fully discharged. No dice. The INV_ON signal isn't being asserted high.

I'll purchase the EEPROM kit and report back.

[ngth82]

Re: Vizio VO420E - INV_ON signal stays low

EEPROM order placed. It'll arrive Nov 6th. I'll check back after Nov 13th as i'm on vacation.

I also see that there is an EEPROM dump thread. I'll place the new EEPROM on my programmer and add it to the thread

[TVDIYguy]

Re: Vizio VO420E - INV_ON signal stays low

Vizio TV suck in boot up screen when turned on.


Need a little help here... i've been looking for a similar thread but can't find anything.....

I have a Vizio , model number E3DB420VX, and the mother board number is 3642-1462-0150(7b).

After looking and researching on the internet for the last two days it seems that all arrows point to the EEPROM CHIP.. however i can't find the location of the chip and nowhere on the internet is it listed.... question is, IS it on this motherboard or is it integrated like the emachine computers of old.... yes i'm that old. If someone can point out what the location number might be that would be awesome. The only station numbers i have seen that remotely look like eeproms are U2,6,8,10. All others look like something else. I've contacted shopjimmy and anybody else listed and they told me to come here. So here i am. I appreciate all suggestions...

[ngth82]

Re: Vizio VO420E - INV_ON signal stays low

On mine, the eeprom is on the back of the main board.

What are the markings on the parts you identified? Pictures or a line by line breakdown would be helpful. Look at eBay for other potential sources.

[attainteddragon]

Re: Vizio VO420E - INV_ON signal stays low

part eeprom marking will have 24........ or 25......... on it.

[TVDIYguy]

Re: Vizio VO420E - INV_ON signal stays low

All EPROMs I have seen are 8 pin and there are like 5 of them in various sizes .... I'll try to post this pic I took with my phone ... I'll take better ones tonight an see if that helps

[budm]

Re: Vizio VO420E - INV_ON signal stays low

Shopjimmy does not sell the programmed EEPROM for this TV model so that may be hard to find.

[vinceroger69]

Re: Vizio VO420E - INV_ON signal stays low

probably a smart tv with nand chips etc

[TVDIYguy]

Re: Vizio VO420E - INV_ON signal stays low

It is a smart tv.... A and all the locations for EPROMs they "look" fine no burns or swelling ... Is it a programming issue ? And if I can't find the correct programmed EEPROM then buy a new board ?

[TVDIYguy]

Re: Vizio VO420E - INV_ON signal stays low

The only one I see that has a 20's number is this one ...... N28