My Viewsonic VX924 monitor died!

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

No, I haven't. Is it a voltage regulator?

[bonney]

Re: My Viewsonic VX924 monitor died!

it's a MBR10100CT Schottky

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

How do i test this?

[retiredcaps]

Re: My Viewsonic VX924 monitor died!

How do i test this?

With power off and LCD unplugged, set your multimeter on diode test function.

pin 1 = left
pin 2 = middle
pin 3 = right

1) Black probe on pin 1, red on pin 2 record diode measurement
2) Red probe on pin 1, black on pin 2 record diode measurement
3) Black probe on pin 3, red on pin 2 record diode measurement
4) red probe on pin 3, black on pin 2 record diode measurement

A good diode should measure between 0.4 to 0.7 V in one direction and 0L (or "1") in the other.

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

Hmmmm, I've been reading newbie1's thread. Since I'm targeting the SMPS controller on my board. I checked the chip using the pins that newbie1 tested. Pins 1+3 bounced around 16.5-18.6v and pins 1+7 was similar in behaviour but bouncing between 13.5-15.5v.

Since PlainBill stated that the SMPS won't start until pin 7 reaches around 16v, I'm wondering if it actually is the SMPS controller that's dead.

I'll be back asap with the schottky.

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

Ok, I tested the MBR10100CT. No matter which way I put the probes on which ever pins, the reading starts at around "230" and very quickly drop to "000". Basically, almost exactly the same as touching the probes together. Yep, sounds like I'm doing it wrong, but I swear I'm not

[retiredcaps]

Re: My Viewsonic VX924 monitor died!

Ok, I tested the MBR10100CT. No matter which way I put the probes on which ever pins, the reading starts at around "230" and very quickly drop to "000". Basically, almost exactly the same as touching the probes together.

And this is with the multimeter set on the diode test function? On your multimeter, it is the same function dial as the 2000 ohm setting (which I personally hate). You only need the 4 measurements I outlined.

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

On your multimeter, it is the same function dial as the 2000 ohm setting (which I personally hate).

Correct, does that mean I am doing it wrong? Because no matter what I do, the meter just drops to 000.

[bonney]

Re: My Viewsonic VX924 monitor died!

I would use a analog multimeter set it to times 10k ohm range, then you should get full reading one way and a little reading the other way

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

Unfortunately, I don't have an analogue multimeter.

Hmmmmm. I'm a bit stuck. What do you wizards think?

[PlainBill]

Re: My Viewsonic VX924 monitor died!

Unfortunately, I don't have an analogue multimeter.

Hmmmmm. I'm a bit stuck. What do you wizards think?

I'm puzzled. The easy approach would be to hook up a source of electricity from Gnd to the 12V output of the power supply and monitor the current as the voltage is increased. You should be able to increase it to 5V or so with very little current draw. I have a 25V variable supply, so that's easy for me to suggest. If you don't, I'd take a 6 or 9 V battery and hook it up (Remember polarity!!!) and see if the battery voltage stays at 9V. If it drops, there is a problem.

PlainBill

[retiredcaps]

Re: My Viewsonic VX924 monitor died!

Correct, does that mean I am doing it wrong? Because no matter what I do, the meter just drops to 000.

I have only used 2 multimeters in my life. Both are autoranging and both give different results than what you are seeing.

I don't know what 000 means on your meter. Maybe check your manual to see how to do diode test. BTW, 220 could me 220mV. I won't have access to my boards or a multimeter this weekend to see if 220mV is a good measurement or not for that type of diode.

You can try a resistance test to see if the diode is shorted or not.

With power off and LCD unplugged, measure pins 1-2, 1-3, and 2-3 using 200 ohms scale. If the reading is less than 20 ohms, that suggests the diode is shorted.

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

Ok, I dug out the manual to my dmm. This is how it reads:

"DIODE MEASUREMENT

1. Red lead to "V (OHM symbol) mA". Black lead to "COM". (Check)
2. RANGE switch to (diode symbol) position. (Check)
3. Connect the red test lead to the anode of the diode to be measured and the black test lead to the cathode.
4. The forward voltage drop in mV will be displayed. If the diode is reversed, figure "1" will be shown."

To be honest I am utterly confused by this, result are variable when I touch the pins, dropping to 000 with each pin combination. These are the results of the diode test that I have collected anyway:

Black pin 1, red pin 2 = -254 - drops to 000
Red pin 1, Black pin 2 = 230 - drops to 000
Black pin 3, red pin 2 = -242 - drops to 000
Red pin 3, black pin 2 = 372 - drops to 000

I also did the resistance tests that retiredcaps asked for with the resistance range set to 200 ohms:

Pins 1+2 = 00.3
Pins 1+3 = 00.2
Pins 2+3 = 00.3

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

I decided to recheck everything. Starting from the 12vdc out I checked the voltage and noticed something strange. If I check the voltage using the 12v and ground pins I get no reading whatsoever. If I do the same I but I use the grounding around the mains socket or around a screw hole, I get the fluctuating tiny voltage of 0.02 - 0.08 that I mentioned in post #22. What does this mean?

[alexanna]

Re: My Viewsonic VX924 monitor died!

Ok, I dug out the manual to my dmm. This is how it reads:

"DIODE MEASUREMENT

1. Red lead to "V (OHM symbol) mA". Black lead to "COM". (Check)
2. RANGE switch to (diode symbol) position. (Check)
3. Connect the red test lead to the anode of the diode to be measured and the black test lead to the cathode.
4. The forward voltage drop in mV will be displayed. If the diode is reversed, figure "1" will be shown."

To be honest I am utterly confused by this, result are variable when I touch the pins, dropping to 000 with each pin combination. These are the results of the diode test that I have collected anyway:

Black pin 1, red pin 2 = -254 - drops to 000
Red pin 1, Black pin 2 = 230 - drops to 000
Black pin 3, red pin 2 = -242 - drops to 000
Red pin 3, black pin 2 = 372 - drops to 000

I also did the resistance tests that retiredcaps asked for with the resistance range set to 200 ohms:

Pins 1+2 = 00.3
Pins 1+3 = 00.2
Pins 2+3 = 00.3

When you check the 5 and 12 voltage, do not use the mains ground. Use the low voltage ground, a ground screw.On the diode check and the ohm reading of the MBR10100CT you may have to lift one leg of it out of the circut to get a accurate reading.
Al.

[bonney]

Re: My Viewsonic VX924 monitor died!

Do you get a reading set at 20K

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

Ok, to save hassle I removed the diode from the board.

This time the diode test looks like this

Black pin 1, red pin 2 = 1 (out of range)
Red pin 1, Black pin 2 = 190 stable
Black pin 3, red pin 2 = 000 stable
Red pin 3, black pin 2 = 000 stable

Resistance looks like this:

Pins 1+2 = 1 (out of range)
Pins 1+3 = 1 (out of range)
Pins 2+3 = 00.5

Does that make any sense?

[alexanna]

Re: My Viewsonic VX924 monitor died!

Recheck your measurements with the diode test
Red pin 1 black pin 2
Red pin3 black pin 2
Do not let pin 2 come into contact with pins 1 our 3 when testing.

[NeiltheDruid]

Re: My Viewsonic VX924 monitor died!

I rechecked. There's no change on the multimeter.

[bonney]

Re: My Viewsonic VX924 monitor died!

Black probe to middle pin (2) red to 1
Black probe to middle pin (2) red to 3

Red probe middle pin (2) black to 1
Red probe middle pin (2) black to3

what are the readings