Swedx LCD XV1-19TVW - screen flash loop

[ocf]

A friend gave me this TV to look at, it recently started exhibiting an issue, when switched on it appears to be stuck in some sort of burn in mode. The screen flashes in a loop between black, white and then RGB Stripes going from dark to light showing across the screen.

It definitely appears to be a test or burn in mode as there are no artifacts or other issues showing on the screen.

TV takes 12v DC external power

There were a few burst 220uf caps on the mainboard that I replaced but this didn't make any difference.

I cant find any schematics on the board or service manual, there are also no replacement boards form the usual sources.

Interesting thing to note, when I heated the board with a hot air gun and powered the TV on it did not show the colour loop and started up ok, I got the swedx splash screen and the TV accepted commands from the remote. After 10 seconds of staying on it immediately went back to the flashing burn in mode. Definitley something faulty on the mainboard, what would be affected by heat like this? Do EEPROM chips only react well to cold?

Any advice on what to check next? I have a good grounding in reading schematics and would consider myself far from a beginner when it comes to electronics, throw some ideas at me!

thanks in advance

OCF

[ozzy214]

Re: Swedx LCD XV1-19TVW - screen flash loop

Sounds like you need to reflow the mainboard. Heating it up may have cleaned up some broken solder joints.

[ReeceyBurger123]

Re: Swedx LCD XV1-19TVW - screen flash loop

Sounds like a faulty regulator, have you tested them ?

[ocf]

Re: Swedx LCD XV1-19TVW - screen flash loop

Sounds like a faulty regulator, have you tested them ?

No I haven't done any checks on these, I'm not great at picking out parts and testing without a schematic.

If I post an image of the board can you point out the voltage regulators.

All the best

OCF

[ocf]

Re: Swedx LCD XV1-19TVW - screen flash loop

Sounds like you need to reflow the mainboard. Heating it up may have cleaned up some broken solder joints.

I'm quite sure that the board didn't get close to any temp that would allow solder to melt. Board probably got about 60-80C max.

I have an SMD hot air station on the way which should help me narrow down the issue as I could heat individual parts.

Thinking to start with the voltage regulators as suggested by ReeceyBurger123

[ocf]

Re: Swedx LCD XV1-19TVW - screen flash loop

Sounds like a faulty regulator, have you tested them ?

I've located all the voltage regulators on the board they are all CX1084 and CX1117 and all labeled ADJ. I have taken a look at data sheets for the chip and I cant work out what voltge the Adjustable regulators should be outputting. Does the output voltage depend on the resistor used between Adj and Output terminls or do I have this all wrong

Voltage regulator part numbers I found on the board -

CX1084 ADJ 7226Y
CX1084 ADJ 7265Y
CX1117 ADJ 7382Y


Any advice welcome, would pictures help?

[ocf]

Re: Swedx LCD XV1-19TVW - screen flash loop

pics, most of V Regulators are on right hand side of board if that helps

https://postimg.org/image/tmomz5h4n/
https://postimg.org/image/ipnbadud3/
https://postimg.org/image/ryphki393/

[ocf]

Re: Swedx LCD XV1-19TVW - screen flash loop

One of the regulators is showing 0.15v on input pin, 0.9 on gnd and 2v on output, this seems wrong?

Dont vregs take a minimum voltage above the required output voltage to drive the regulator itself, so if this has 0.15v and 2v output surely its problematic?

I'm spitballing here, just trying to make sense with my limited knowledge

[ocf]

Re: Swedx LCD XV1-19TVW - screen flash loop

any further help please?

[ReeceyBurger123]

Re: Swedx LCD XV1-19TVW - screen flash loop

Ok that reg you tested is good, the tab is normally the output on them. What about the others ?