Troubleshooting Viewsonic vx2235wm

[PlainBill]

Re: Troubleshooting Viewsonic vx2235wm

Th3_uN1Qu3, alexanna, Kostamojen, you guys ROCK!!! I go out running a few errands, got a fender dented in a parking lot, and came back home to find the problem has (mostly) been solved.

Kostamojen, good work!!

PlainBill

[Kostamojen]

Re: Troubleshooting Viewsonic vx2235wm

the fuse does NOT show a short in either polarity direction. Sounds like a bad fuse? Where can i find a replacement? and do you have to de-solder the fuse to remove it?

[alexanna]

Re: Troubleshooting Viewsonic vx2235wm

A good fuse will show a short,0 ohms.
Test like you checked the capacitors, try reversing the leads of the ohmmeter

[Kostamojen]

Re: Troubleshooting Viewsonic vx2235wm

Check the Glass fuse next to the "I" capacitor.

When I test the fuse in question, the ohms shoots to 0 briefly, then drops to the left side of the meter.

[alexanna]

Re: Troubleshooting Viewsonic vx2235wm

Check the Glass fuse next to the "I" capacitor.

[Kostamojen]

Re: Troubleshooting Viewsonic vx2235wm

GOOD NEWS! during my last inspection of the circuit board, I noticed a solder bridge near the capacitor labeled "I" (the one that was obviously shorted). After removing the solder bridge, the short is gone. I re-assembled the monitor and now get power light indicators (blue when a PC is connected, orange sleep-mode when no PC is connected). However, there is no picture. I shined a flashlight on the screen, and can see a ghost image of the signal being sent from the PC.

[Kostamojen]

Re: Troubleshooting Viewsonic vx2235wm

Ran the test as laid out by PlainBill. I started by calibrating the MM, per instructions. The results are shown in the attached photos. One photo shows the results, the other photo shows the lettering key (NOTE: picture take prior to cap replacement, but the same lettering was used).

Ohms readings under 50 were investigated, however, only one time did the two readings match (at 0 ohms for cap "I"). In all other cases, the needle stayed at the far left side or would briefly pop to the 200-40 ohms range, then return to the far left side.

What do you think PlainBill? Any conclusions?

[Th3_uN1Qu3]

Re: Troubleshooting Viewsonic vx2235wm

Bill, top notch help as always. Leaving this one to you.

[PlainBill]

Re: Troubleshooting Viewsonic vx2235wm

I thought I might have a difficult time describing the readings I'm getting (since I myself don't really know what I'm looking at). So I've taken some photos of the test results. Hopefully you can interpret the results for me.

The first photo was taken with the MM in it's default state (only the ground probe connected). Each consecutive photo shows the MM reading with the positive (red) probe touching the positive lead of each of the new caps.

I got different results from different caps, so I'm guessing there is a problems somewhere, just that I don't know how to interpret where the problem is.

Thanks again.

There are a couple of things going on here. Most of them are easily solvable.

First, you are on the X10 scale. That means you take the reading on the top (green) scale and multiply it by 10. So while the first reading showed .8, it actually is reading 8 ohms. That is low, but because of other factors, I will call it an alert - something to be investigated - not necessarily a cause for alarm.

Next, the meter must be properly zeroed. The first photo shows a label 'Ohms Adjust', and what appears to be a button on the side of the meter. You must clip the leads to the same point, then adjust the meter so the needle is exactly on 0 on the ohms scale (the green scale).

Another point - a VOM uses a much higher voltage (typically a 1.5 volt battery) to measure resistance than a DMM (typically less than .2 volts), so it will cause diodes and transistors to conduct, throwing off the reading. More on this later.

Lastly, the ohms scale is a reverse scale. This can cause confusion when making readings. In the first reading (second picture) the needle is between .7 and .8, so the actual resistance is about 7.7 ohms.

The capacitors are large enough that the VOM may take an appreciable time to charge them. If the needle appears to be drifting, wait until it either stabilizes, or drifts into the good (to the left of 20) area.

These are not insurmountable problems. Electronics technicians used VOMs to test solid state equipment for decades before DMMs became available at reasonable prices. All you have to do is apply a few tricks.

1. Leave the meter on the X10 scale. Ignore any reading where the needle is to the left of the 20 (greater than 200 ohms).

2. Adjust the meter properly for 0 ohms

3. You can take pictures if you wish, or just write down the resistance, or just write down the needle position and multiply later.

4. Any readings below 50 ohms should be investigated. To investigate, simply swap the leads - red to the ground point, black to the capacitor lead. If both readings match, it's a real resistance. If they don't, the higher resistance is the one to use.

PlainBill

[Kostamojen]

Re: Troubleshooting Viewsonic vx2235wm

That's an analog meter you have there (and a cheap one at that). Are you sure it is in good working order? Soldering looks clean, there could be something else affecting the readings. If you are positive there are no solder bridges and no reversed caps plug it in and try it out. It won't blow up anyway. If it works, then you need a new meter.

I tried powering up the monitor after replacing the caps, and I got no power lights or screen power (see my first post from June 25, 2011). That's why I'm trying to troubleshoot the board. I'm assuming that I messed something up while doing the repair (created a short, or something). It appears that the only caps that are showing a reading above 0 ohms are CE108 and CE109. would that tell you anything? or do I need to go pickup a new digital multimeter?

[Th3_uN1Qu3]

Re: Troubleshooting Viewsonic vx2235wm

That's an analog meter you have there (and a cheap one at that). Are you sure it is in good working order? Soldering looks clean, there could be something else affecting the readings. If you are positive there are no solder bridges and no reversed caps plug it in and try it out. It won't blow up anyway. If it works, then you need a new meter.

[Kostamojen]

Re: Troubleshooting Viewsonic vx2235wm

I thought I might have a difficult time describing the readings I'm getting (since I myself don't really know what I'm looking at). So I've taken some photos of the test results. Hopefully you can interpret the results for me.

The first photo was taken with the MM in it's default state (only the ground probe connected). Each consecutive photo shows the MM reading with the positive (red) probe touching the positive lead of each of the new caps.

I got different results from different caps, so I'm guessing there is a problems somewhere, just that I don't know how to interpret where the problem is.

Thanks again.

[Th3_uN1Qu3]

Re: Troubleshooting Viewsonic vx2235wm

Maybe I'm doing the measuring wrong. Do I touch the black and red leads to the cap leads sticking out the bottom of the board?

All caps in a monitor (except the big cap after the mains side rectifier) are going to have their negative side at case ground potential. Just find a ground (metallic ring on screw hole = good idea) and use an alligator clip for the black probe on your multimeter. Then just use the red lead to probe the positive leads of the caps. It's a lot easier handling one probe than it is two.

[Kostamojen]

Re: Troubleshooting Viewsonic vx2235wm

It's not destroyed.

Was that a typo? You indicated you measured greater than 3 ohms. Did you mean < (less than) 3 ohms? A reading of under 3 ohms definitely indicates a problem.

PlainBill

Maybe I'm doing the measuring wrong. Do I touch the black and red leads to the cap leads sticking out the bottom of the board? How do the polarities on the mm leads need to match up to +/- leads of the cap? Please be specific as I'm pretty new to this. Thanks.

[PlainBill]

Re: Troubleshooting Viewsonic vx2235wm

Finally had some time to hit this thing with the multimeter. Only one cap indicated a possible short (>3 ohms). It's the 220uf 25v cap at CE109? I also just remembered that this is where my hand slipped and the solder tip dragged across a couple circuits. It looked superficial to me, I hope I didn't kill the board. I'm posting a picture of the area so you can look at it. It looks like a faint white line. Please tell me i don't destroy it.

It's not destroyed.

Was that a typo? You indicated you measured greater than 3 ohms. Did you mean < (less than) 3 ohms? A reading of under 3 ohms definitely indicates a problem.

PlainBill

[Kostamojen]

Re: Troubleshooting Viewsonic vx2235wm

Finally had some time to hit this thing with the multimeter. Only one cap indicated a possible short (>3 ohms). It's the 220uf 25v cap at CE109? I also just remembered that this is where my hand slipped and the solder tip dragged across a couple circuits. It looked superficial to me, I hope I didn't kill the board. I'm posting a picture of the area so you can look at it. It looks like a faint white line. Please tell me i don't destroy it.

[999999999]

Re: Troubleshooting Viewsonic vx2235wm

While the burst capacitors are an obvious problem, that it failed (somewhat) concurrent to a power outage suggests there might have been a power surge that potentially fried the logic board. Because you have had the lights flicker, there is no doubt the fuse isn't (or at least wasn't at the time) blown.

[Th3_uN1Qu3]

Re: Troubleshooting Viewsonic vx2235wm

Sorry for being such a noob. I'm very interested in learning how to do this, and you're help is much appreciated. Thanks again.

At this point you assemble the monitor and try it out. In some cases, not all voltages will come up without the logic board connected. Testing the voltages is not required in this case. Unless you haven't done any obvious mistakes (caps in backwards, lower voltage caps on higher voltage rail), it should be good to go.

[jetadm123]

Re: Troubleshooting Viewsonic vx2235wm

While you're measuring resistances, try measuring the resistance across the main fuse, F101? It's a small square box mounted behind the the main power plug. It should measure under 1 ohm.

[momaka]

Re: Troubleshooting Viewsonic vx2235wm

1) I did create a solder bridge at one point while connecting the new caps, but I corrected the problem before the monitor was tested. And I don't think there are any solder blobs, but I'll check again.

2)All connectors were securely connected and double checked. No screws that appear to be shorting anything.

3) I was VERY careful to observe polarity on the board. I created a schematic before removing the old caps, and followed it carefully. Even double checked everything before the test.

4) I'm going to borrow a multimeter and check the voltages next.

Excellent!

I've borrowed a multimeter, but, to be honest I don't really know what I'm doing here. I'd appreciate an explaination of the process of testing the voltages.

Well actually, before you even test the voltages, first measure resistance between the leads of the caps your soldered and see if you find any short circuits (i.e 3 ohms or less, depending on how good your multimeter is).

If you don't find any shorts then you can test the voltages. But first some safety tips...

See that thick black line on the top of the board where the logo "Delta" is (or alternatively that white line on the bottom of the board)? - that line differentiates between primary and secondary side. On the primary side, high-voltages will be present when the PSU is plugged in so DO NOT touch anything with your hands on that side when the PSU is plugged in. The primary side is the one where that big 400v cap is located.
Also avoid getting your hands near the inverter transformers - that's those near the blue ceramic capacitors and CCFL connectors.

Fortunately, the voltages you will be measuring first are located on the secondary side - i.e. the low voltage side. Whenever measuring voltages on the secondary side, the black probe of your multimeter should always be placed on ground. The screws that tie down the PSU as well as the metal body of the monitor are all ground points you can use. With the red probe, you measure whatever voltage you want to measure.

Now, I would really like to tell you what voltages to measure, but for that I need to know what voltages this PSU outputs. This piece of information can usually be found on the connector that gives power to the video board. In fact, based on the first pic your posted in this thread, you can see that some of the pins on that connector are indeed labeled. Please post what those labels are.
Normally most monitors will have a 5v and a 12v rail (with the 12v rail sometimes given as 13v or 15v, depending on the monitor/PSU). Occasionally, some monitors will have a standby rail too (usually 5v), but I don't think this is the case with this monitor. Therefore, the 5v and/or 12v rail should be present at all times when the monitor is plugged it.

Should the board be connected to the rest of the monitor components when I test the voltages?

Yes.