MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

[glutton4punishment]

LCD monitor 19" man. 2006. Two VGA and one DVI sockets.

The power on LED never comes on.

When I first got it this week, it worked fine for 5 minutes. I turned it off, and when I came back to it a few minutes later, it started to malfunction, see numbers 1 & 2 below for description.

I opened it up, and found two bad caps. (They're marked with the yellow arrows.) After I replaced the two caps it now gives me the following behavior:

1. If no cable is plugged into the VGA sockets, or if plugged into VGA "#1", I get a black screen. If I press ANY of the control buttons, for as long as I press on it, I get a grey screen. If release any button, the screen reverts to black.

2. If I plug into VGA socket "#2", I get a black screen. This time, if I plug into any of the buttons, I get either:
a. a black screen; b. a grey screen; c. a grey screen with very fine vertical colored lines.

I've searched for this one, but I can't find it.

The board is browned out near to where I replaced the caps, but other than that nothing looks unusual. Except on one chip, labeled IC 201, there appears to be a white substance (runaway glue?). It's marked in the pics, again with a yellow arrow.

thanks a million!

[selldoor]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Have you tested the fuses I see 2 but thought there should be 3 on this board


Later- I see it now - 2 white small cylindrical and one red block

Also on the logic board top right in your picture there is a small smd fuse with a T on it.

Later still - can I assume you replaced the caps the right way round - they have polarity.
also what make/series caps did you use - from a reputable seller?

[jetadm123]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Also check zener diode ZD203 (last photo/ left side) for a short. For this board, it's across the 5V output and is known to short out.

[glutton4punishment]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

thanks for the replies!


1. the 2 white fuses and the black SMD with the T on top check out OK. The red block reads 76 ohms. (That's the one next to the power cord jack, right?)
2. the new caps are CapXon brand. (the old ones are xunda, and one small su'scon)
3. yes, I installed the new caps polarity correctly
4. zener diode test using the diode tester on my voltmeter, black lead on black end of diode (red lead on red end of diode) :
0.136V; leads reversed: 0.439V

hmm.. ZD2 reads 0.739/0 V;
ZD204= 0.575/0.920; (leads normal/reversed).

so I'm confused. Is ZD2 the only good one?

[selldoor]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Red block fuse is dead, jim. For testing you can use another type of fuse of same amps and voltage as near as you can get.
I dont understand diode test readings I always use ohms. jetadm123 will know.
If there is any doubt, you need to lift one end off the board or the whole thing if any chance of snapping it and re-test.


EDIT re fuse - having said that if the fuse has failed I cant understand how you are getting anything on the screen even if just lines. Better CAREFULLY test the voltage across the legs of the BIG cap HIGH voltage.

[jetadm123]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Do as selldoor suggested and remove ZD203 and test in ohms mode.

[glutton4punishment]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

now the red block fuse reads full continuity.

ZD203 is 292 ohms one way, no continuity w/leads switched.

just for fun,

ZD2 reads no continuity in either direction
ZD204 reads no continuity in either direction

[selldoor]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

What does it say on the meter when you are saying no continuity OL "1" on the left hand side or something else - what ohms scale are you using - should be 2000.

Are ZD2 and ZD204 off the board as well?

[glutton4punishment]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

although it's not at hand, my digital VOM doesn't have a 2000 setting, just regular, k, and M ranges.

I've been reading it at regular, not high, ohm settings.

When I say no continuity, that means 0L. Continuity means 0.5 ohms or less.

I haven't taken anything off the board yet, all readings are in circuit.

Thanks for your patience!

[selldoor]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Can you post a picture of your meter and if its not clear from the picture tell us the make /model The test results are inconclusive as we dont know what scale you are testing on. It will report OL if overscale.

[glutton4punishment]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Again, in circuit, with the VOM on the "k"Ohm scale, (thousands of ohms), ZD203 reads 0.73 kOhms in both directions. That means 730 Ohms either way.

If the ZD is bad, what can I do? Is there a way for me to know what value it is?

And getting back to my original post, why would pushing any button make a difference? Why isn't the power on LED lighting?

Thanks!

P.S. I brought my camera's memory card to work, but my computer here wouldn't read the card, so here's a link to a pic of my VOM. (BTW, it's an auto ranging VOM). In the picture, on the right of the display is a ohm symbol (omega). When you push the RANGE button, it goes from "omega" to "k omega" to "M omega". I hope this is clear!

[selldoor]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Ok I have the manual for your meter and setting seems ok.
Are the batteries in it good - I ask as each time you test something the value
seems to change.


This result means it is is probably OK
ZD203 is 292 ohms one way, no continuity w/leads switched.

This One
ZD203 reads 0.73 kOhms in both directions. That means 730 Ohms either way.

Means it is NOT ok


BUT it does suggest it is not shorted or open

But why is it so different - Need to take it off the board to eliminate nearby components messing up the test

[glutton4punishment]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

OK, so I got ZD203 off the board. It's not my problem.

It reads 23.x M ohms leads one way; 0L with the leads reversed (on the "M" ohm scale).

It also passes the diode test, 0.753V leads one way, 0L reversed.

[selldoor]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Good - put it back in.
With it all connected up and switched on can you test the voltage on each side of the small flat fuse on the logic board with respect to ground screw. Also can you test the voltage on each pin on the connector power to logic.
Have to ask - you did have cable from logic board to panel connected.
Next with the power off disconnect that cable and see if backlight comes on

[glutton4punishment]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Good - put it back in.
With it all connected up and switched on can you test the voltage on each side of the small flat fuse on the logic board with respect to ground screw.

Assuming you're talking about the one with the "T" on it, DCV is 17.05 on both sides

Also can you test the voltage on each pin on the connector power to logic.

I'm assuming you mean "power" board "to logic" board.

In the new picture, the connector is about 9:00 on the far left end of the power board.

Looking from the side of the board without components; I'm listing in pairs, Left/Right, STARTING from the pair closest to the edge of the board, ENDING in the pair closest to J202

(L/R)
(17.05/17.05)
(0.6mV/0V)
(5.08V/250mV) note, right side climbed to 250mV, then started descending.
(0.6mV/4.25V)
(80mV/0.6mV)

Have to ask - you did have cable from logic board to panel connected.
I assume "LCD" panel... yes, connected.

Next with the power off disconnect that cable and see if backlight comes on

I don't know when the power is on or off, since the power on LED doesn't work. What happens is that if I push and hold ANY of the control switches, the backlights come on. If I release the buttons, the backlights go off. I can toggle the backlights off and on like this.

I disconnected the cable from the logic board to the LCD panel and it made no difference, push any button to get backlights, release any button to turn off backlights.

[selldoor]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Assumptions correct -getting too late here - wondering if the button board is ok? Just to keep you interested I have just got one of these power supplies in a monitor - freeby as it had been recapped but wouldnt come on. I think he had replaced the 4 caps in a square with ones a shade taller and the logic board wouldnt seat down onto the power board at the connector.
I am a bit loathed to take it apart in case I unfix it but it might come to that and I can
test parts on mine and see how we compare. Just hope we dont end up with 2 non working

[glutton4punishment]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

thanks for the offer, but it's not worth the shipping!!

why do you think the problem is with the power board?

I was contemplatiing switching out the rest of the caps on the power board, but don't know if the problem is there or on the logic boards...

I don't have enough experience/knowledge to know what to do!

[selldoor]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

Some misunderstanding there - I wasnt offering you the board I wss only suggesting that I test components on mine which I know is working fine and
you do parallel tests on yours.

I dont think there is anything wrong with the power supply ( it does after all power the backlights) in fact if the button board is ok then seems like it has to be the main board. I dont know what main my monitor has - I thought I had pictures but cant find them at the moment.

[glutton4punishment]

Re: MAG T906W Black Screen, Grey Screen, Vert. Lines, you name it!

My bad.

I'll test my button board over the weekend.