Vizio VX42L Progress?

[chummyb]

I have been pouring over the TV repair threads for weeks now, and watching YouTube videos about these Vizio TV's and am stumped.

First off I have little to no background in electronics, but am very familiar with using DMM's and soldering equipment and the like. I am an A&P Mechanic so I know how to follow directions and look for discontinuities

My symptoms are similar to everyone else's in that the TV will turn on (Logo from orange to white) but that is the only response I get, and the set must be unplugged to reset (or press the reset button on the main PCB). I have checked the fuses and voltages on the main board and get 5.23v Standby, and a full 12.12 for power. LDO Regulators are as follows:

Ident - Vin - Vout - Vreg
U2 - 5.19 - 2.37 - 1.47 AMC1117
U8 - 5.21 - 3.33 - 2.07 AMC1117
U33 - 5.19 - 3.35 - 2.08 AMC1117
U7 - 3.35 - 1.3 - 29mV AMC1117
U9 - 3.35 - 1.54 - 1mV K1117515 ?? Fixed v. Adjustable?

Besides U9 I found the rest of the voltages to be in range, but what do I know!

PSW_ON Voltage is at 3.15

I see no evidence of bad caps (no leaks, buldges, etc) and besides visual cues have no way to test said caps.

All of the voltages going to the ccfl ballast board are on target and the two fuses on said board test ok as well. When power button is pressed you can hear the faint click of the relay to power the ballast board, but no action. BUT when I unplugged the center harness from the power supply (both the center and right/colored wire harnesses feed the ccfl ballast) to test voltages at the supply, the ccfls illuminated!
Same problems exist with the TV but with that harness unplugged the backlight will come on.

Has anyone had any success with a problem such as this?!? The TV was free and I don't really have money to dump into buying new control boards, chasing unknown problems (I'm just an A&P Mechanic, memmer?) but I am willing to troubleshoot, and even learn a bit along the way if someone has knowledge to share!

Attached are (crappy) pictures of the guts of the tv for your viewing pleasure, but know I'm about as good at taking photos as I am with diagnosing TV faults.

Any help would be greatly appreciated!

[retiredcaps]

Re: Vizio VX42L Progress?

Ident - Vin - Vout - Vreg
U2 - 5.19 - 2.37 - 1.47 AMC1117

Please confirm the readings and part number for U2. If they are correct, it is bad.

U2 is an adjustable voltage regulator and it is bad. Pin 2 should be pin 1 + 1.25V

Either pin1 is too high or pin2 is too low. That is 2.37-1.47 = 0.90V difference.

[retiredcaps]

Re: Vizio VX42L Progress?

Ident - Vin - Vout - Vreg
U9 - 3.35 - 1.54 - 1mV K1117515 ?? Fixed v. Adjustable?

U9 is fixed. The part number/datasheet tells you so. Namely, the 15 at the end indicates it is fixed at 1.5V output.

[kevinm34232]

Re: Vizio VX42L Progress?

I can tell you this is common with Vizo main boards and just replaced a newer main board from model SV370XVT with similar issue. I did not have S/M with schematics so all I could do was compare voltages and there was 2 that I found problems with. But that's as far as I could go without more info.. The majority of s/m's you find are incomplete, around 30 pages where the complete one is 170+ pages.. I just spent the $60 on a new board and all is good...

[budm]

Re: Vizio VX42L Progress?

"Ident - Vin - Vout - Vreg
U2 - 5.19 - 2.37 - 1.47 AMC1117
U8 - 5.21 - 3.33 - 2.07 AMC1117
U33 - 5.19 - 3.35 - 2.08 AMC1117
U7 - 3.35 - 1.3 - 29mV AMC1117
U9 - 3.35 - 1.54 - 1mV K1117515 ?? Fixed v. Adjustable?"

The LDO if it is adjustable type, the Voltage between Vadj and the Vout should always be 1.25V (this is from internal precision 1.25Vref circuits), the typical tolerance is between 1~2% (depends on the manufacturers). Vout = 1.25V + Vadjust. I.E. Vadj to ground = 1.25V, then the Vout should be 2.5V.
U2 voltage does not look right.
Please check the Vadj/Vout pin to see if they are correct when you add up the numbers.
Do you get BL_ON at the inverter connector?
There should be another very small black fuse for this CHI-MEI (CMO) inverter board, see the picture for example.
Please post closed up pictures of the inverter board.

[chummyb]

Re: Vizio VX42L Progress?

Just confirmed U2 voltages and they are as reported. That is a stupid error on my behalf, as I thought I had checked and rechecked everything and came out with those differences but thats the blessing of another set of eyes. I will pick up a replacement tomorrow and let you know how it goes.

As far as the LDO regulators go I have seen lots of posts that claim that any part number "1117" is an adjustable regulator? I failed to look up a data sheet for the regulator which would have been the smart thing to do, but is there a general rule of thumb based on this part number?

[chummyb]

Re: Vizio VX42L Progress?

@budm

Yes, the inverter board has that fuse, as well as the 2 white SM fuses. Continuity test said they were good (not open), <1ohm resistance

[budm]

Re: Vizio VX42L Progress?

The fixed regulator will have something like this printed on the body
1117-33 = 3.3V fixed, 1117-18 = 1.8V fixed. The adjustable will be just 1117. Another way to tell is that the Adjustable reg will have a resistor between Vadj pin and Vout pin, and also a resistor between Adj pin and Ground.
How about BL_ON signal?

[chummyb]

Re: Vizio VX42L Progress?

Yes, here is a picture of the inverter board. All three fuses are good. Getting 24.6V at all 3.

[budm]

Re: Vizio VX42L Progress?

You mean you do have about 3V or more at the BL_ON PIN?
There are two connectors on the board.

[chummyb]

Re: Vizio VX42L Progress?

@budm

I do not see a label BL_ON. From the power supply, the multi-colored harness has 5-24V supply, and 5-SGND outputs. On the white harness there are 5-24V supply, 5-SGND outputs, and outputs from pins marked A and B. The outputs from pin A and B are 8mV and 97mV respectively. This is the only signal inputs to the inverter asside from the 24V and SGND.

[chummyb]

Re: Vizio VX42L Progress?

The PSON is an pin on the harness that is directed from the powersupply to the Main PCB. As I understand it, its function is to activate the secondary power from the Power Supply to the Inverter when it gets its 3V input. (Used to close the contactor in the relay mounted on the power supply?)

[budm]

Re: Vizio VX42L Progress?

The A and B label are for Dimming and BL_ON, do not remember which one is A which one is B. the dimming is variable DC (0v = min brightness, 5V = MAX brightness), BL_0N = 3V or more for lights on. A and B are routed through the power supply board for clean wiring setup.
Theses two signals are generated by the main board.
For the backlights to work, the inverter needs two main things: Switched 24VDC which is turn on by the PS_ON from the main board, and then the BL_ON signal to turn on the inverter circuits.
You should be able to Ohm out the A and B wires back to the connector on the main board.
At this point it looks like you are not getting the BL_ON signal.
Can you provide the model number of the panel, the spec sheet will tel you which pin on the inverter board is the BL_ON pin.

[retiredcaps]

Re: Vizio VX42L Progress?

Just confirmed U2 voltages and they are as reported. That is a stupid error on my behalf, as I thought I had checked and rechecked everything and came out with those differences but thats the blessing of another set of eyes. I will pick up a replacement tomorrow and let you know how it goes.

You weren't the first and won't be the last to make the above mistake. I see a lot of message that state "all the regulators check out", but people never post the actual readings so now I ask.

There is also a chance the regulator is good, but the cap feeding pin 1 is bad.

[chummyb]

Re: Vizio VX42L Progress?

I see, I was able to trace the wires back to the main PCB, and they still only give me readings around 10mV and 98mV at the pins on the main PCB side. Possibly the bad voltage from the U2 LDO Reg is messing with the circuit responsible for this output and locking up the controls?

[budm]

Re: Vizio VX42L Progress?

The LDO voltages has to be corrected first before going further. Bad reading can be due to bad LDO or bad filter caps around the regulators.

[chummyb]

Re: Vizio VX42L Progress?

@retiredcaps

I guess I will play it "better safe than sorry" on that one. There is only one specialty electronics shop that I know of here in Tucson that may or may not carry the parts I need and it is all the way across town for me. I was debating pulling the cap to make room to work on replacing that Reg, so might as well pull it and buy a replacement while I am there.

Thanks again for your time and knowledge! I really appreciate the help!

[retiredcaps]

Re: Vizio VX42L Progress?

There is only one specialty electronics shop that I know of here in Tucson that may or may not carry the parts I need and it is all the way across town for me.

Depending on how much gas is and what you get for mileage, I would consider ordering from digikey. It costs about $2.75 ish for 1st class mail and you typically get your order in 48 to 72 hours.

I suggest getting at least 2 regulators, maybe 3 for backup/spare, as they are relatively cheap.

[retiredcaps]

Re: Vizio VX42L Progress?

The fixed regulator will have something like this printed on the body
1117-33 = 3.3V fixed, 1117-18 = 1.8V fixed. The adjustable will be just 1117. Another way to tell is that the Adjustable reg will have a resistor between Vadj pin and Vout pin, and also a resistor between Adj pin and Ground.

Another hint. Don't get fooled if you only see 1117. Sometimes the fixed part on the 2nd line of the chip. So on the chip, it might look like

1117
25EA

where 25 on the second line denotes 2.5V fixed output.

That is why we always ask for all the part numbers and clear focused photographs so we can read what is written on the IC.

[budm]

Re: Vizio VX42L Progress?

@retiredcap, thanks for reminding that, one sure way if I see two resistors connected to the LDO, then I know it is not fixed regulator.