Dmtech LCD DML-4137WD

[PowerAmpFreak]

Please see the attached picture.
It's a 37" LCD tv DMTECH model DML-4137WD.
The screens shows all flickering lines in different colours. No OSD info shows.
The powersupply output voltages 'seems' ok.
When powering the set on, the screen may work ok for the first 5-10 seconds. The DVD tray also works during this period. When the screen go bad, also the DVD tray is not possible to eject, which makes me think of either powersupply problems or main controller board issues.
Appreciate any advice.

[PlainBill]

Re: Dmtech LCD DML-4137WD

Please see the attached picture.
It's a 37" LCD tv DMTECH model DML-4137WD.
The screens shows all flickering lines in different colours. No OSD info shows.
The powersupply output voltages 'seems' ok.
When powering the set on, the screen may work ok for the first 5-10 seconds. The DVD tray also works during this period. When the screen go bad, also the DVD tray is not possible to eject, which makes me think of either powersupply problems or main controller board issues.
Appreciate any advice.

My first thought was 'Ohhh, psychedelic, has the TV been eating mushrooms, dude?'

Then I remembered I'm supposed to be a responsible member of the community. Given the fact that the DVD tray is not working, it doesn't sound like a failure of the T-con board. I'd say either one of the myriad 3 terminal regulators or a processor itself is bad.

PlainBill

[Dgtech]

Re: Dmtech LCD DML-4137WD

Hmmmm...... 5 - 10 seconds of normal activity and then failure? Do you smell anything like components heating up? If you do take this one apart, check for some discoloration of either board. Take some pics and post em. I hope we all can help.

[PowerAmpFreak]

Re: Dmtech LCD DML-4137WD

If memory serves me right, I actually felt "hot" smell from somewhere. Also a rattling sound is heard, thought this coming from the high voltage parts.
I'll continue investigation.

[PowerAmpFreak]

Re: Dmtech LCD DML-4137WD

It seems the 3,3V regulator is having a problem, or possibly overloaded. It will heat up in about 10 seconds, then probably reach temp protection and output voltage begins to drop. Hopefully there are a problem with the regulator itself.
It's a simple switcher, LM2576 placed on the logic control board.

[Dgtech]

Re: Dmtech LCD DML-4137WD

What is the input voltage to this regulator? The data sheet found on the site below shows that the maximum input voltage should be 45VDC. I'd desolder this regulator to get an accurate measurement of the applied input voltage (Pin 1).

[Wizard]

Re: Dmtech LCD DML-4137WD

On LCD Vcc is usually 5V or 12V. This switching regulator, datasheet is out there for it and measure ohms between ground and switching regulator inductor's output, you may able to find shorted capacitor or eeek, bad IC that voltage is feeding into.

Remember, some of them had regulator feeding another lower voltage regulators in series. Check all from that feed, you may find the overload by much lower resistance or too low volt (leaky).

Cheers, Wizard

[PowerAmpFreak]

Re: Dmtech LCD DML-4137WD

Got back to this set today. See attached picture. I found a voltage regulator which is fed from the 3,3V output (from the LM2576) and it looked strange. When trying to desolder it's 'INPUT' leg from the pcb, the leg and part of the case went off, so I believe this buddy has caused the initial problems.
Unfortunately I cannot figure out which device this is. It's marked '1117SJ', may it be a +1,7V regulator?
Now when trying to start up the set, the 3,3V is there but interrupted after about 2 seconds, then comes back on for 2 seconds and so on.
I guess this is due to the 1.7V regulator is out of the circuit and logic is detecting a problem (incorrect voltage).

[PlainBill]

Re: Dmtech LCD DML-4137WD

Got back to this set today. See attached picture. I found a voltage regulator which is fed from the 3,3V output (from the LM2576) and it looked strange. When trying to desolder it's 'INPUT' leg from the pcb, the leg and part of the case went off, so I believe this buddy has caused the initial problems.
Unfortunately I cannot figure out which device this is. It's marked '1117SJ', may it be a +1,7V regulator?
Now when trying to start up the set, the 3,3V is there but interrupted after about 2 seconds, then comes back on for 2 seconds and so on.
I guess this is due to the 1.7V regulator is out of the circuit and logic is detecting a problem (incorrect voltage).

It's an AMC117SJ from ADD Mictrotech Corp. The datasheet is available here. You will have to decode the second line of the part number to identify the output voltage - it's not 1.7 volts.

PlainBill

[PowerAmpFreak]

Re: Dmtech LCD DML-4137WD

Great! Thanks for that, Bill. It appears the regulator is an adjustable one, since it's just an "1117SJ" without additional text.

[PlainBill]

Re: Dmtech LCD DML-4137WD

Great! Thanks for that, Bill. It appears the regulator is an adjustable one, since it's just an "1117SJ" without additional text.

Maybe, maybe not. Check the resistance from pin 1 to ground. If it reads less than an ohm it's a fixed output regulator.

PlainBill

[Dgtech]

Re: Dmtech LCD DML-4137WD

My only question is whether this is a defective part or burned open from some other problem on the board?? I hope this will fix it but just in case, buy an extra regulator in case this scenerio exists.

[PowerAmpFreak]

Re: Dmtech LCD DML-4137WD

Today this TV got new life. I used an LM1117-ADJ which is close enough. Everything is OK now. It was this bastard that overheated the LM2576.
Grrrrrreaat!