Vizio VX32L No picture, sound, or backlight

[tom66]

Re: Vizio VX32L No picture, sound, or backlight

Oh, I initially said the CPU survived it... But maybe it got damaged?
Try on HDMI. If that works, the analogue part of the chip is shot -- no analogue sources will work.

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

Well, I'm pretty sure my issue has something to do with a fried or damaged board. At the new regulator, I'm getting

3.29
1.65
1.25

I disconnected the adjust jumper from the board and get the same readings. With the jumper disconnected, I get the same results with the video input. Either I'm not getting the adjust pin connected to the board properly, or the board is fried.

What do you guys think?

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

Oh, I initially said the CPU survived it... But maybe it got damaged?
Try on HDMI. If that works, the analogue part of the chip is shot -- no analogue sources will work.

I've only got one HDMI component and that won't work on the 720p units. AVG is analog isn't it?

[budm]

Re: Vizio VX32L No picture, sound, or backlight

It should have 2.5V out put if the adjust pin is at 1.25V. It can due to it is not LDO regulator.

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

It should have 2.5V out put if the adjust pin is at 1.25V. It can due to it is not LDO regulator.

Unfortunately, I don't know enough about regulators to know what you are saying.

[budm]

Re: Vizio VX32L No picture, sound, or backlight

This is the way to figure out if the adjustable regulator is good or not:
Notes: we are looking at the regulator with the Big tab up (the big tab is tied internally to the center pin).
Adjustable regulator will have two resistors attached to it, one resistor (Rfb) is between pin1 and pin2, another resistor (Rg) is between pin1 and ground. Pin3 is an input pin.
The voltage between the Adjust pin (left pin) and the center pin (Pin2, output) will always be 1.25V +/- 2% (this is the precision voltage reference), if it is not, it is bad.
To figure out what the output voltage should be: measure the voltage between pin 1 and ground and add 1.25V to that number, that is the output voltage on pin 2 but you have to make sure you do have 1.25 between pin 1 and 2 as noted above

[tom66]

Re: Vizio VX32L No picture, sound, or backlight

ADJUST must be grounded. The regulator will then output 1.25V, but only if it is loaded sufficiently (it requires minimum of about 10mA to regulate.) To ensure it is loaded tie a 120 ohm resistor to ground.

The output of all adjustable LDOs, as well as adjustable linear regulators, is Adjust+1.25V.

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

So, with the adjust disconnected, I should have 1.25V at the out. And if I don't, the regulator is bad? If I do, the board, or at least the analog section of the board is shot?

[tom66]

Re: Vizio VX32L No picture, sound, or backlight

No, not disconnected. It MUST be grounded.

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

Got it. Out of curiosity, why a 120 ohm resistor? Why not jut tie it to ground?

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

Never mind, I see. Current draw?

[tom66]

Re: Vizio VX32L No picture, sound, or backlight

120 ohms must go to ground from the output. This provides 1.25/120 = 10.4mA current draw, which is within the minimum specified.

So the INPUT goes to 3.3V or 5V, depending on which works.
The OUTPUT goes to the OUTPUT of the ex-regulator.
The ADJUST goes to GROUND.

A capacitor of 100nF minimum is required on the output. Input capacitance is also a good idea.

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

I'm getting the 3.3 off the resistor that originally supplied it to the damaged regulator pad. The output is jumped back to the original spots too. I'm going to try to ground the adjust. I don't have a 120 ohm resistor, but I do have a 1k potentiometer adjusted down to 120 ohms. If it works, I'll pick up an actual resistor tomorrow.

[tom66]

Re: Vizio VX32L No picture, sound, or backlight

You can use a lower value, but probably no lower than 10 ohm, as it would have to dissipate a lot of heat. (10 ohm = 0.144W; maximum for a 1/4W resistor is... 1/4W or 0.25W.)

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

Well, the good news is the regulator works like it's supposed to. The bad news is there's still no video signal.

So going back to an earlier question. Does the 4a, 4b suffix on the main board part number make a difference?

[budm]

Re: Vizio VX32L No picture, sound, or backlight

There should be existing resistors between the ADJ and OUT pin, and Adj and ground, unless those tiny resistors got damaged or removed during the installation of the replacement LDO.

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

There should be existing resistors between the ADJ and OUT pin, and Adj and ground, unless those tiny resistors got damaged or removed during the installation of the replacement LDO.

Yeah, the adjust resistor must have gotten damaged.

[johnboy1313]

Re: Vizio VX32L No picture, sound, or backlight

So going back to an earlier question. Does the 4a, 4b suffix on the main board part number make a difference?

Doesn't matter, the board sold.