Viewsonic VX2255WMB Grey Screen

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

Oh youre right, I remeasured the transformer S1 and S2 came to 620 ohms, S3 and S4 came to 618 ohms. Using the red probe on S1 and black on S2. The guide before told me to use black on S1 and red on S2 which didnt give me a reading, i must of measured it upside down.

In regards to the Tcon, there is a blown smd fuse "N" which was replaced by the previous owner. The originally SMD fuse was "K".

Heres the thread where the previous owner troubleshooted the white screen.
https://www.badcaps.net/forum/showth...ight=VX2255WMB

Where can I buy a new SMD fuse of the same specifications (SMD "K")? I'll replace it and see if it works, but rereading the previous owners thread, the source of the blown fuse was not yet found.

[retiredcaps]

Re: Viewsonic VX2255WMB Grey Screen

Using the red probe on S1 and black on S2. The guide before told me to use black on S1 and red on S2 which didnt give me a reading, i must of measured it upside down.

When measuring resistance in the above scenario, it does not matter which way the probes are placed on. Try it again.

I suspect you had no reading because you used the 200 scale. When the resistance reading is 620 ohms, your multimeter will show a "1" on the left hand side. That is why you need to set it on 2000 ohms.

Where can I buy a new SMD fuse of the same specifications (SMD "K")?

Digikey.com if you are in the USA. They have friendly people who answer phones and can help you find the correct replacement. 1.800.344.4539

[retiredcaps]

Re: Viewsonic VX2255WMB Grey Screen

Thanks - got it now.

When I'm tired, I sometimes don't make sense and logic goes out the window. Working on multiple threads also can lead to confusion once in a while.

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

Well i tried either direction but one direction wont give me a reading no matter how much i increased the range. I started at 2k and went up to 2m but it still showed a 1 on the reading.

[retiredcaps]

Re: Viewsonic VX2255WMB Grey Screen

Well i tried either direction but one direction wont give me a reading no matter how much i increased the range.

Please post a picture of your multimeter.

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

Well i just went out to work wont be home til around midnight but this is the meter im using http://www.microcenter.com/single_pr...uct_id=0207743

[retiredcaps]

Re: Viewsonic VX2255WMB Grey Screen

On your multimeter notice that the diode test function is shared with the 2K ohms function and possibly the other ranges with the exception of the 200 ohms. I wonder if your multimeter somehow is doing a diode test function instead of an ohms reading?

A diode test function is designed to apply voltage across a diode to ensure the diode only allows current flow in one direction. Thus, when you reverse the probes you should get "1" in one direction and a reading between 0.5 and 0.8V in the other.

Your multimeter, because of the shared design (ohms and diode on the same dial), may be incorrectly applying voltage instead of measuring resistance.

My 3 multimeters at home have all the ohms and diode test function separated. For example, I have an used Fluke 75. See picture.

I also looked at the DVM850 manual online and it is useless in terms of discussing this operational aspect.

PS. I have a huge interest in multimeters and that is the reason for this sidetrack.

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

Even so if i increase the range off 2k and to 20k wouldnt it measure 0.06? Unless the diode is being used along with all the resistance test

[retiredcaps]

Re: Viewsonic VX2255WMB Grey Screen

Even so if i increase the range off 2k and to 20k wouldnt it measure 0.06? Unless the diode is being used along with all the resistance test

In the post above, I revised my first sentence and you probably didn't see the edit.

You would think that 20K should show 0.06, but your multimeter may still be doing a diode test? It could also be malfunctioning too? Again, there is nothing the manual that discusses the operational aspect of the shared dial functionality.

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

Well i just tried it one more time, and it seems to be working properly now hmm odd.

[retiredcaps]

Re: Viewsonic VX2255WMB Grey Screen

Well i just tried it one more time, and it seems to be working properly now hmm odd.

Maybe you have a low battery or your probes are fraying internally causing some intermittent contact?

https://www.badcaps.net/forum/showpo...9&postcount=30

[selldoor]

Re: Viewsonic VX2255WMB Grey Screen

In regards to the Tcon, there is a blown smd fuse "N" which was replaced by the previous owner. The originally SMD fuse was "K".

Heres the thread where the previous owner troubleshooted the white screen.
https://www.badcaps.net/forum/showth...ight=VX2255WMB

Hi, Im sorry, When I read the original
"Funny it seems that I find a post with the same monitor I am working on as of now! So I guess its been worked on before and I found its past history.

https://www.badcaps.net/forum/showthr...ight=VX2255WMB

https://www.badcaps.net/forum/showthr...ight=VX2255WMB"

I just skimmed it and didnt realize you meant THE EXACT SAME BOARD.
That is what your saying isnt it.
I will now re read the other posts.

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

Yes that is what i was trying to say, its the exact same monitor

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

Question, is there a specific direction fuses have to be in? I'm guessing no, but just making sure.

[PlainBill]

Re: Viewsonic VX2255WMB Grey Screen

Question, is there a specific direction fuses have to be in? I'm guessing no, but just making sure.

If doesn't matter.

PlainBill

[momaka]

Re: Viewsonic VX2255WMB Grey Screen

Where can I buy a new SMD fuse of the same specifications (SMD "K")?

Digikey.com and Mouser.com both should have it.

About the specifications:
- K indicates the current rating - 1.5A in this case. Any fuse with that current rating will do.
- The voltage rating is irrelevant since most SMD fuses are rated for 32V or above while the t-con uses typically 5V.
- To get an exact replacement, measure the original fuse length and width in mm. The size is the actual case style. For example, a fuse that measures 1.2 mm length by 0.8 mm width usually comes in a "1208 (metric)" case style. If you can't find your fuse on Digikey or Mouser, post the size of it here and we can help you find it.

In any case, once you find the fuse, buy at least 2 of them. Judging by codeMoneky's thread, I would say get 4. They are cheap anyways.

Also, since you posted this:

Well i just tried it one more time, and it seems to be working properly now hmm odd.

There's two reasons for this:
1) flux on component leads
2) Cheap/bad probes

To eliminate the issue with 1), just scrape the component leads with your probes a little before trying to measure.
2) cannot be eliminated easily without changing the probes, but at least you can get an idea of how bad they are - choose lowest resistance scale and hold the metal ends of the two probes together, then move the probe wires around while still holding the probes together. If the readings on the meter fluctuate, your probes are not very good. If the readings stay low (close to 0), then your probes should be okay.

Just to be sure, re-test your fuse a few times. Use lowest resistance setting. And just to be clear, you do this with the monitor turned off and disconnected from the wall. If it's good, leave it in there for now. An N-type SMD fuse is rated for 2A.

On your multimeter notice that the diode test function is shared with the 2K ohms function and possibly the other ranges with the exception of the 200 ohms. I wonder if your multimeter somehow is doing a diode test function instead of an ohms reading?

My 830D multimeter does a similar thing for the 2000 and 200 Ohm scales, even though Diode test is on its own separate setting. If there's a diode in the circuit, it will attempt to measure the resistance of diode first (numerically, the resistance on my meter (in Ohms) is usually similar to the voltage drop (in mV)). If there is only a resistor, it will measure the resistor.
Perhaps his does a similar thing. But for testing fuses, it wouldn't really matter anyways because the meter will show a low reading for both situations.

[selldoor]

Re: Viewsonic VX2255WMB Grey Screen

Hi - right- ive re read and from what I can see the important points are.
1 codemonkey had the screen working as a single screen and it only went off when using in a multiple monitor setup.
2 When codemonkey gave up the monitor was working but with a white screen.
3 You say it is working with a grey screen - is that still the case? Can you post a photo of the panel lit
4 in codemonkeys post he said: Here's what bammbammfran.com had to say:

f1 fuse on lcd screen board
If you mean the long narrow board that is attached to the back of the screen ? (first- that board is not removable) Second: if that is the fuse that is popping, then that board is more than likely the problem. Probably has a dead short in it somewhere, Ohm it out and you might be able to verify this.
You can check to see if too much voltage is getting to that fuse, but I have my doubts. Most screens are around 5 volts dc. I have seen a couple that run higher, but not often.
If the problem was in the dac board, it probably would not stay lit at all, if it stays on white screen then it is probably ok

5 codemonkey then checked the tcon and found a number of shorted resistors - he says:
I've checked EVERY single resistor on this monitor. I've come across 9 resistors that were shorted. However, I don't know the proper resistance measurements so if some one has the same monitor and can check I'd greatly appreciate it. There is I realize, a possibility that some of the resistors have to low a resistance for me to measure, but again I need some sort of confirmation. (I'm using a Mastech MS8268 DMM.) Picture 1 is of the video control card with the shorted resistors marked and picture 2 is of the LCD board that's attached to the screen. Where possible, I've marked what I think the resistances might be based on other resistors nearby. This is only done if there is a line of several resistors with the same value that lead me to believe that one shorted in the same group would have the same value.
Shorted resistors in question:

Pic 1:
R78 96.2KΩ (maybe, should be ?)
R22 ???
R39 ???

Pic 2:
R100 ???
R101 ???
R102 ???
R15 ???
R95 33Ω (maybe, should be ?)
R97 33Ω (maybe, should be ?)

6 We dont know if he changed them - I guess not.

SO I dont know if your meter is up to checking these resistors again but if you can, do so.
Please also post decent pictures of your tcon and perhaps one of our "screen advisors" Alexanna might join in and suggest some test points that your meter can cope with.

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

Well I just replaced the fuse, the white screen is gone but now I would turn on the monitor (blue power light on) and it would instead get flashes on and off with a bunch of random oriented color lines and then it would turn off again (blue light goes off and red light comes on) Would the graphics board be the cause of this? What usually causes the monitor to go off, shouldn't it stay on when connected to a computer with the screen on, but it keeps shutting off after 3 seconds?

For the resistors I measured again.

R78 0.4Ω
R39 0.4Ω

Tcon

R100 0.4Ω
R101 0.4Ω
R102 0.4Ω
R15 0.4Ω
R95 0.4Ω
R97 0.4Ω

On the picture showing R22, It wouldnt give me a reading. I'm guessing it was the only one replaced. I tried to reflow the solder but it still won't give me a reading (won't change off 1). I'm guessing it has a bad solder connection or its a faulty part. I ended up wicking it off and trying to measure it again but still no reading. I also had this same problem with the K fuse, i didn't try to reflow but i just replaced it.

How would i find the actual values for these resistors if they need replacing?

[momaka]

Re: Viewsonic VX2255WMB Grey Screen

When resistors fail, they go open-circuit, not short circuit!

The component you circled in the picture above looks like an inductor or a jumper resistor (a resistor with no resistance - those are used quite often to jump over traces on the board). The silkscreen on the board should tell you what it is. R = resistor, L = inductor, C = capacitor, D = diode. Jumper resistors with 0 resistance can still be marked with R.

If anything, it's the ceramic caps that usually fail shorted. A white screen usually implies something is wrong with the power supply on the t-con board. The shot above shows the video/logic board. That can cause a white screen too, but it's rare. You can check by seeing if 5v is coming to the fuse on the t-con board.

Have a look at the thread below. It's a different monitor, but in post #13 (look at long version), I explain what generally goes wrong with these t-con boards and what causes the white screen/gray screen issue.
https://www.badcaps.net/forum/showthread.php?t=17904

From the picture of your t-con you provided, you can even see some of the test points I mentioned in the above thread. Namely VCC1 (left side of the picture), V5V (next to "N" -marked fuse you removed), and VAA (upper right corner of your picture). All you have to do is measure the resistance and the voltage going to these points and report your findings back here. Test point VCC1 is likely at 1.8V or 3.3V, V5V should be at 5V, and VAA somewhere between 9V and 15V (depends on the design). Also, it is worth to note that test point VAA on your monitor is the equivalent to AVDD in the above thread.
There should be 2 more test points that are important. I will need to see more pictures of your t-con, though. Most likely, you will find these test points named as VGH and VGL or VGG and VEE.

[tieny]

Re: Viewsonic VX2255WMB Grey Screen

The component i circle was labeled R22, so i'm guessing its a jumper resistor that failed (no reading, and no continuity). (I'll need some help trying to find a replacement.)

I found all the specific points you asked for (voltages and resistance)
I had a problem measuring the voltage though, since the monitor kept turning off (blue power led to red) after 3 seconds, the voltage would drop back down to zero. I had to probe the points and turn on the power to measure the voltages before it went off. Most of the time it stablized at a value except for VGH.

VCC1: 2.51V, 457Ω
VAA:12.7V, 1336Ω
VGL: 6.9V, 712Ω
VGH: 19-20V fluxuating, 962Ω

For the fuse, I measured 5.04V going into it.