SOYO (mt-prtpt3208nb) lcd tv garbled screen

[raymond]

Turns on nicely to a bright blue screen, menu works but seems a little snowy compared to the background blue. In all viewing modes though the image is incomplete as though it's not getting all of the necessary info ( similar to a computer screen set to the lowest possible settings with a limited color palette). Both the main and power boards look good with no bulging caps or burns. I haven't gotten down to t-con board yet. One reading on the PSU rail to the main board is 4.4 V(red wire) -seems odd.
Any ideas as to where to start looking will be appreciated. Thanks.........Ray

[tom66]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

Have you tested the LDOs?

Are those caps on the main board Panasonic? Seems surprising for such a cheap brand.

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

What are LDOs?

The biggest caps are purple Hermeis, the two mid sized ( center right) are brown Hermeis, the rest are black Hermeis.

[tom66]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

What are LDOs?

The biggest caps are purple Hermeis, the two mid sized ( center right) are brown Hermeis, the rest are black Hermeis.

Ah yeah, so using the same vent, but a crap brand..

Anyway, an LDO is a voltage regulator. Basically: Voltage comes in, less voltage goes out. It drops the voltage to a specific value e.g. 1.8V, 2.5V, 3.3V.

I've highlighted some LDOs on the board. (Check the bottom too - there may be more.)

With the TV powered on. Turn your multimeter to the 20V setting. Test each pin of each circled regulator, and note the voltages. Also note down the part number written on the device if you can make it out. Post your results.

Then we can go from there and see if any regulators are bad. If they are, they can be replaced.

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

OK, I will do that. Thank you
I just now tried to turn it on from a cold start (unplugged state). The green led light came on but the screen didn't light up after 2 minutes. I tried again 3 times quickly, it lit up on the third try. What does that indicate?

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

Here's a view of the screen. As mentioned in previous post it takes a few tries to start from a cold state but once it's been on it restarts as it should.

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

LDOs on main board

Start top left ....moving clockwize

1117-3.3sj ( 0, 3.28, 5.15 )

1117-1.8sj ( 0, 1.78, 5.15 )

78do5al eetka1 ( 12.36, 0, 4.96 )

1117-3.3sj ( 0, 3.28, 5.14 )

1117-1.8sj ( 0, 1.78, 5.14 )

78do5al eetka1 ( 12.37, 0, 4.99 )

[tom66]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

LDOs on main board

Start top left ....moving clockwize

1117-3.3sj ( 0, 3.28, 5.15 )

1117-1.8sj ( 0, 1.78, 5.15 )

78do5al eetka1 ( 12.36, 0, 4.96 )

1117-3.3sj ( 0, 3.28, 5.14 )

1117-1.8sj ( 0, 1.78, 5.14 )

78do5al eetka1 ( 12.37, 0, 4.99 )

All of those look good.

Did you say the OSD/menus look the same?

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

No, the menus look much better but not as crisp or solid as they should look.
Any other ideas......anyone ?

[tom66]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

No, the menus look much better but not as crisp or solid as they should look.
Any other ideas......anyone ?

Well, as the problem is less severe on the menus, it's very likely not the T-con.

The easiest solution will be to replace the main board, if you can source a replacement.

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

Thanks for the info tom66 (your input is greatly appreciated)
The slow to start thing ... I can hear a slight whine from the PS when it's trying to start.
I wondering if it could be a bad cap without noticeable bulging.

[Dgtech]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

I would change out the Tconn board. Just as a good guess.

[tom66]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

Thanks for the info tom66 (your input is greatly appreciated)
The slow to start thing ... I can hear a slight whine from the PS when it's trying to start.
I wondering if it could be a bad cap without noticeable bulging.

Do you have an oscilloscope?

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

Do you have an oscilloscope?

No, I don't have an oscilloscope....just a multimeter

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

I would change out the Tconn board. Just as a good guess.

It might come to that....I'm hoping it's an easier fix though.

[tom66]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

Can you show a pic of the "almost clear" OSD?

Also, does the effect appear on black/dark scenes, and if so is the OSD affected?

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

The effect is constant in all light conditions. Here's 2 pics of the menu with and without a background image. The menu appears to get partially absorbed into the background.

[tom66]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

I'm trying to think - maybe the menu has a "transparency of OSD" option and that is what is causing the effects on the menu?

[Dgtech]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

Since you are having the same problem with the OSD and the picture, It seems like the problem is either going to be in the Tconn board or the ribbon cables that go to and from it. Those items are common to both.

[raymond]

Re: SOYO (mt-prtpt3208nb) lcd tv garbled screen

I'm trying to think - maybe the menu has a "transparency of OSD" option and that is what is causing the effects on the menu?

Thank you tom66, you were right, it was set on halftone. The menu is now crisp and on top, nice to see. The screen image is still rough (as seen in this new pic), it has large pixel like squares flickering all over the screen. Would it be a good idea to replace those larger Hermei caps on both boards?