Prima (lv-2628p) Dotted grid accross screen

[raymond]

I have a prima 26" lcd tv with a grid of dots across its entire screen which makes it unusable.
The menus come up on top as they should but the grid appears in every mode of use. Loosening and shifting the t-con to panel board ribbon cable shows a white screen or a vertical striped multi-colored screen depending on it's position.
The back light and the sound works. I need help solving this problem, please.

[tom66]

Re: Prima (lv-2628p) Dotted grid accross screen

Is the grid of pixels constant, does it move over time, between inputs or after turning on or off?

Are the pixels embedded onto the source video or do they just replace it?

Loosening the T-Con connector and seeing vertical lines is to be expected. I don't think the T-Con is bad.

There are several things that can cause this. One is the voltage regulators on the main board, or the buck converters for the CPU - these are reasonably easy to fix with just basic soldering experience. Another is a bad RAM or a bad BGA device, which are more difficult ot fix. The easiest solution, although a bit expensive, is to replace the entire main board, which is very likely to be where the problem is.

If you have a part number for the main board, that will help in locating the part.

[raymond]

Re: Prima (lv-2628p) Dotted grid accross screen

The grid is constant running horizontally ....green dotted lines about 1/4" apart over whole screen and appear in every mode except when on the component selecting screen. As soon as it's getting input from a device or in tv air mode the grid is on top of the image.
Could you point out or describe the voltage regulators and buck converters please. Thanks............Ray

[tom66]

Re: Prima (lv-2628p) Dotted grid accross screen

The grid is constant running horizontally ....green dotted lines about 1/4" apart over whole screen and appear in every mode except when on the component selecting screen. As soon as it's getting input from a device or in tv air mode the grid is on top of the image.
Could you point out or describe the voltage regulators and buck converters please. Thanks............Ray

I need a bigger picture of the main board, some of them are quite small.

Also, have you checked power supply output voltages? It's unlikely to be the cause, but it will eliminate the power supply being at fault.

[japlytic]

Re: Prima (lv-2628p) Dotted grid accross screen

The OSD seems OK; it looks like a processing problem (bad memory, maybe?)

[raymond]

Re: Prima (lv-2628p) Dotted grid accross screen

Here's a larger pic of the main board. I could use some advise in checking the output voltages on the powersupply (How and where) I have a multimeter. thanks............Ray

[PlainBill]

Re: Prima (lv-2628p) Dotted grid accross screen

Here's a larger pic of the main board. I could use some advise in checking the output voltages on the powersupply (How and where) I have a multimeter. thanks............Ray

It is extremely unlikely the problem is with the power supply; it is almost certainly on the main board.

I've circled 3 LDO regulators in yellow. What are the part numbers of these? If there are any more similar parts, what are those part numbers?

Testing is easy. With the tab to the top, the pins are numbered 1, 2, 3 left to right. The tab is identical to pin 2, so it is not necessary to measure it.

I've circled a yellow / green wire and mounting screw in black. Use that for the negative lead. With the TV power on, measure the voltage on the three pins of each Ic, and report them and the part numbers.

PlainBill

[tom66]

Re: Prima (lv-2628p) Dotted grid accross screen

Also, check this diode too. It's unlikely to be the problem, as you are getting something on the display, but it will help eliminate faults. There is a vague possibility that a lack of good supply voltage provided by the switcher would lead to a poor picture.

To check the diode: Set your multimeter to diode test. Place red on one end, black on other. Record reading. Reverse leads. Record reading. You should get something like "1 ." or "OL" for one measurement (which is good) and a value from 200 - 800 for the other.

[raymond]

Re: Prima (lv-2628p) Dotted grid accross screen

Readings for the ICs and a diode marked in picture

Big IC top-left is 3.93, 5.17, 8.41 (AZ1084s -ADJE1 711J62)

Two ICs lower r-center are both 0, 3.28, 4.97 (AMS1117 3.3 0817)

Right side IC .26. 1.50, 3.24 (AMS1117 0815)

Diode circled in red 1, 331

[PlainBill]

Re: Prima (lv-2628p) Dotted grid accross screen

Readings for the ICs and a diode marked in picture

Big IC top-left is 3.93, 5.17, 8.41 (AZ1084s -ADJE1 711J62)

Two ICs lower r-center are both 0, 3.28, 4.97 (AMS1117 3.3 0817)

Right side IC .26. 1.50, 3.24 (AMS1117 0815)

Diode circled in red 1, 331

All of those regulators are good.

PlainBill

[raymond]

Re: Prima (lv-2628p) Dotted grid accross screen

Thank you PlainBill. Nice to be making some progress. Does anyone have any other Ideas or suggestions. I'm all ears and in learning mode. Ray

[PlainBill]

Re: Prima (lv-2628p) Dotted grid accross screen

Thank you PlainBill. Nice to be making some progress. Does anyone have any other Ideas or suggestions. I'm all ears and in learning mode. Ray

Only the one which has already been mentioned. The problem is clearly occurring on the main board. It is probably a failure in one of the ICs. Determining which one and replacing it is going to be very difficult. At this point my suggestion is to replace the main board.

PlainBill

[raymond]

Re: Prima (lv-2628p) Dotted grid accross screen

Could there be a problem with these two ICs on the T-con board ?

Upper one is AMS1117 0815 .............Reads 1.24, 2.49, 4.59

Lower one is AMS1117 3.3 0817 ........Reads 0, 3.31, 4.94

[tom66]

Re: Prima (lv-2628p) Dotted grid accross screen

Could there be a problem with these two ICs on the T-con board ?

Upper one is AMS1117 0815 .............Reads 1.24, 2.49, 4.59

Lower one is AMS1117 3.3 0817 ........Reads 0, 3.31, 4.94

As OSD is correct it is unlikely to be the problem.

Upper one is adjustable and is the 2.5V reg.

Lower one is fixed and gives 3.3V.

[cashkennedy]

Re: Prima (lv-2628p) Dotted grid accross screen

In other words the T-con board doesnt know what its displaying input wise / or OSD. So it wouldnt display 1 input wrong and the OSD correct. The main board is the only part that handles inputs and the OSD seperately / differently.

[PlainBill]

Re: Prima (lv-2628p) Dotted grid accross screen

One other point - sometimes there will be LDO regulators on the back side of the main board. Those should be checked, too. If you do not find any bad regulators there, you really are reduced to replacing the main board.

PlainBill

[raymond]

Re: Prima (lv-2628p) Dotted grid accross screen

Ok, Thank you
I will try that next. ........Ray

[raymond]

Re: Prima (lv-2628p) Dotted grid accross screen

A question:
What sort of voltage numbers would indicate a bad voltage regulator?
.........Ray

[PlainBill]

Re: Prima (lv-2628p) Dotted grid accross screen

A question:
What sort of voltage numbers would indicate a bad voltage regulator?
.........Ray

There are two types of LDO regulators - fixed and adjustable.

Fixed regulators will have numbers something like AS1117-33 or AP1084-25. The number after the dash indicates the output voltage - 3.3 or 2.5 volts respectively. (There are also 1.8 and 1.25 volt variants of each).

Adjustable regulators do not have the digits indicating output voltage. The output voltage will be 1.25 volts above the ADJ pin - pin 1 on the 1117 type regulators.

PlainBill

[raymond]

Re: Prima (lv-2628p) Dotted grid accross screen

Ah! Thank you very much for sharing that, PlainBill. I'll keep that for future reference.
..........Ray