Viewsonic VX1935WM

[vx1935wm]

Hello,

In case you haven't already guessed, the monitor I am having problems with is the Viewsonic VX1935WM. The (inverter? well, the one where you plug the power cable into) board is a revision 1, not revision A or D.

I've read several threads on this board so far, and I realize that I'm not the first, and unfortunately, neither will be the last to have this problem. My monitor was affected by the monitor turns on for a second, then blanks out problem. Specifically, the blue light stays blue, and I can faintly make out what's onscreen, but the backlight has crapped out.

I've already replaced all the CapXon capacitors with Panasonic FM capacitors, with the exception of the physically large 100 μF 400 V capacitor, so the pictures posted are pre-recapping. Unfortunately, I still have the same problem.

From threads on other models of Viewsonic monitors, I realize that the cold cathodes or some other components can have problems, too. Unfortunately, I'm an electronics newbie and am unable to adapt the advice presented on those threads to my specific monitor.

I'm rather limited in the equipment I have (for example I don't have access to a multimeter at the moment) but would appreciate advice involving the multimeter anyway, because I will have access to a DMM in a few weeks. However, until then, I obviously won't be able to test anything.

Hopefully, I haven't left out any information. I can take more pictures, focus on specific parts, different angles, etc. However, the camera I am using is rather old, so I am not sure picture quality can get much better. Hopefully it's good enough. In any case, thanks to all in advance.

CapXon CapXon CapXon

[jetadm123]

Re: Viewsonic VX1935WM

Your problem may be caused by one or more of the following:

1) bad inverter transformer

2) one or more bad ccfl tubes or wiring

3) failure of a device(s) in the protection circuit


To check the inverter transformer, with power off and monitor unplugged, set your meter on resistance and measure across the points circled in yellow (you'll have to find a way to get around the grey silicon covering the test points) . If your readings are say more than 3% difference, the transformer may be bad.

Check the CCFL wiring to make sure there are no broken or frayed wires. To check the CCFL tubes, you will need a spare working tube that you can substitute for the existing tubes. Again, with power off, unplug one of the 4 tubes from the power supply and plug in the working tube. Power up monitor and if you have backlights, then you've found the bad tube. If not, try this test for the other three tubes.

Failure of a device in the protection circuit is much more difficult to find, so try the first two methods before anything else.

[retiredcaps]

Re: Viewsonic VX1935WM

There seems to be some solder ring cracks on the inverter transformer? The most obvious to me is the one just left of R121 and underneath R123 on the backside.

You may want to reflow or resolder those joints and retest.

A guide for troubleshooting 2 second to black is at (starting with post 13 and 14)

https://www.badcaps.net/forum/showthread.php?t=10419

Concentrate on #4, 5, and 6.

[vx1935wm]

Re: Viewsonic VX1935WM

Thanks all for your advice. Regardless of whether my skill level is enough to fix the monitor, I already consider myself to have benefited greatly. I've not soldered until now, so that's one more thing I've learned. The worst case is I only end up with some soldering experience and a dead monitor, but I still consider that a gain.

As mentioned before, I don't have the tools with me yet, and won't have them for several more weeks. I'll keep your suggestions in mind, and will refer to them when I do get my hands on a multimeter.

As I don't have a spare CCFL tube, would unplugging each tube one by one be a viable way to test the monitor? By that I mean unplug the first one, power up the monitor, see if it doesn't die out in two seconds... iterate through the next three tubes. I can unplug them at the inverter board, so I don't have to disassemble the monitor further, and therefore it should be relatively quick to test... assuming this is a viable test method.

Basically, I just want to (safely) test the monitor in any way I can with the tools I have on hand. Once again, I am a complete electronics newbie, so I'm thankful for all your advice and will defer to your greater knowledge.

Oh, and as for the inverter transformer, that's the big yellow thing that sits roughly in the middle of the board, surrounded on three sides by the capacitors I replaced? If so, I think I see six pins for that on the underside of the board. If so, I will check the resistances between all combinations of those pins when I get my hands on a multimeter.

[jetadm123]

Re: Viewsonic VX1935WM

As I don't have a spare CCFL tube, would unplugging each tube one by one be a viable way to test the monitor? By that I mean unplug the first one, power up the monitor, see if it doesn't die out in two seconds... iterate through the next three tubes. I can unplug them at the inverter board, so I don't have to disassemble the monitor further, and therefore it should be relatively quick to test... assuming this is a viable test method.

Basically, I just want to (safely) test the monitor in any way I can with the tools I have on hand. Once again, I am a complete electronics newbie, so I'm thankful for all your advice and will defer to your greater knowledge.

Oh, and as for the inverter transformer, that's the big yellow thing that sits roughly in the middle of the board, surrounded on three sides by the capacitors I replaced? If so, I think I see six pins for that on the underside of the board. If so, I will check the resistances between all combinations of those pins when I get my hands on a multimeter.

All 4 ccfl tubes must be connected in order for the circuitry to function properly. Disconnecting one tube at a time will force the sense circuitry to shut down the inverter.

The inverter transformer is the rectangular device on the far right marked "T1".

In post #2, I have circled the points of the inverter transformer that you need to measure. The yellow line connecting the circles are the points you need to measure across.


While you're waiting for the DMM, I would highlr recommend watching some "How to use a DMM" videos on YouTube.

[vx1935wm]

Re: Viewsonic VX1935WM

Ok. T1, T as in transformer, I suppose. Now to pick off the glue and watch DMM tutorial videos.

Thanks for the information. I really appreciate your patience in dealing with me.

[PlainBill]

Re: Viewsonic VX1935WM

One thing you can try is a variation of what you suggested. Disconnect all but one CCFL, turn on the monitor and see if the backlight comes on. It will only be on for a second or two, and the screen will be dim. Disconnect that CCFL and connect the next. Turn on the monitor etc, repeating for all 4 CCFLs. You are looking for one CCFL that does not come on.

PlainBill

[retiredcaps]

Re: Viewsonic VX1935WM

Warning. The voltage around the CCFLs can range from 600 to 1500V. Wait at least 2 minutes when changing the connectors around so everything has a chance to discharge.

I usually use a power bar with a on/off click switch. I power off via the power bar, wait 2 minutes, and then unplug AC power cord. Then I change the CCFL connectors and replug in the AC power cord.

[Th3_uN1Qu3]

Re: Viewsonic VX1935WM

Backlights are driven with AC so no storage capacitors to worry about. Besides, the current is a couple mA so it's not dangerous even if you were to touch it while it was working. By far more dangerous is the big mains filter cap.

[Scenic]

Re: Viewsonic VX1935WM

^ agreed. worst thing that can happen is a small arc from the connectors (if it's turned on and you come too close to the CCFL connectors on the inverter board with your fingers)
it hurts a bit (like a small sewing needle), but it's not really dangerous.

the mains filter cap on the other hand has around 170V DC (120V AC countries) or around 320V DC (230V AC countries) across its legs all the time when the unit is plugged in.. far more dangerous..

[Th3_uN1Qu3]

Re: Viewsonic VX1935WM

Eh, even the main filter cap in an LCD is fairly benign... but i sure wouldn't want to touch one in a computer PSU or TV.

[PlainBill]

Re: Viewsonic VX1935WM

'Fairly benign' is relative. I recall this story about the hazards of high voltage.
Everyone 'knows' that the 2nd anode voltage on a TV picture tube isn't really dangerous, the voltage is too low.

The story goes the electronics student dragged in a console TV to electronics class, and wanted assistance troubleshooting it. The instructor decides to pull the chassis, and asked the student if he'd discharged the CRT. The student says he had, so the instructor reaches in to pop the HV lead. And hits 25,000 volts. When he jerked back, he tore a 6" long gash in his arm.

I've had a few adventures with high voltage myself. I wouldn't try unplugging CCFLs while an inverter was running, but would try swapping CCFL leads while the AC power cord was still plugged in. On the other hand, I'm not going to criticize anyone who prefers to be cautious.

PlainBill

[Th3_uN1Qu3]

Re: Viewsonic VX1935WM

'Fairly benign' is relative. I recall this story about the hazards of high voltage.
Everyone 'knows' that the 2nd anode voltage on a TV picture tube isn't really dangerous, the current is too low.

Fixed that for you.

I meant not dangerous as in "won't kill you" not as in "care not required". It's by no means guaranteed that it won't make you do anything stupid... such as jerking your arm back into something sharp. Regardless, we should all agree that one can start unplugging CCFLs right after the monitor has been powered off.

[PlainBill]

Re: Viewsonic VX1935WM

Fixed that for you.

I meant not dangerous as in "won't kill you" not as in "care not required". It's by no means guaranteed that it won't make you do anything stupid... such as jerking your arm back into something sharp. Regardless, we should all agree that one can start unplugging CCFLs right after the monitor has been powered off.

Thanks for the fix.

Yeah, sudden movements. In the 1970's one of my duties was maintaining a Mass Spectrometer from the 1950's. All of the electronics in this beast used vacuum tubes. The electrolytic capacitors (I believe the manual referred to them as condensers) had octal bases and plugged into sockets (obviously for ease of replacement). My predecessor had replaced most of these by soldering metal can caps to octal bases.

One day the mass spec. isn't working, so I start checking. I quickly spot a 0C3 voltage regulator tube that's flickering. I reach in to pull it and come in contact with the metal can of one of the caps as I'm extracting the tube. The shell happened to be at 180VDC. And the tube went flying. Turned out Earl hadn't done a very good job of soldering. And I had the pleasure of finding a replacement for a tube that had been obsolete for more than 10 years.

PlainBill

[vx1935wm]

Re: Viewsonic VX1935WM

Thanks to all again. I was born in the late 80s, so it's always fun to hear about technologies that are no longer in use (and probably were no longer in use even by the time I was born.)

PlainBill, I will try what you suggested. All your stories encourage me to do it in a very conservative way. Then again, I've already had my brush with electricity. Apparently, when I was just able to walk, I stuck tweezers in the electrical outlet. Glad it was tweezers and not two separate pins. Path of least resistance is my friend.

It's a nice day today, and I'm glad to be around for it

[smason]

Re: Viewsonic VX1935WM

Yes it's low current and the designers of the equipment know that the low current won't do enough damage, so they add sharp metal edges.

[rholliday]

Re: Viewsonic VX1935WM

New to this forum have the same problem as vx1935wm.
How do you remove the cover?

Robert

older than dirt

[retiredcaps]

Re: Viewsonic VX1935WM

How do you remove the cover?

You basically need to pry the thing apart.

Be careful when opening because there may be fragile connections, but this video gives you an idea

http://www.youtube.com/watch?v=Ul5LhuCT1y8