Badcaps.net Forum
Go Back   Badcaps Forums > Electronics Theory and Troubleshooting > Troubleshooting Computer Displays
Register FAQ Members List Social Groups Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 10-22-2010, 09:14 AM   #1
NeiltheDruid
Member
 
Join Date: Sep 2010
Posts: 42
Default My Viewsonic VX924 monitor died!

So, I was just watching some youtubes and my monitor powered off completely with no warning. No flickering, no flashing lights, no smells, no sounds. I tried the power button, nothing. Switched the mains cable, nothing. I'm guessing it's something to do with the power circuitry, so I opened the monitor up and fished out the board. There are a couple of 470uf @25v caps that are bulging quite a bit (pic below). On the other hand I am wondering if the instant powering off has more to do with a fuse blowing rather than bad caps, what do you think?

NeiltheDruid is offline   Reply With Quote
Old 10-22-2010, 09:30 AM   #2
Dgtech
Junior Advisor
 
Dgtech's Avatar
 
Join Date: Apr 2009
City & State: Pittsburgh, PA
My Country: USA
Line Voltage: 120 VAC 60Hz
I'm a: Professional Tech
Posts: 1,260
Default Re: My Viewsonic VX924 monitor died!

Check the fuse but definitly change the caps. If there are any more capxon's on that board (470 and above) I'd change em out too.
__________________
The strong-minded rise to the challenge of their goals,the weak-minded BECOME HATERS

Dgtech is offline   Reply With Quote
Old 10-25-2010, 06:52 AM   #3
NeiltheDruid
Member
 
Join Date: Sep 2010
Posts: 42
Default Re: My Viewsonic VX924 monitor died!

Ok, I've swapped out the two caps that dgtech suggested. I have checked the fuse and that seems to be ok. Unfortunately, I'm still getting nothing. Anyone got any ideas?
NeiltheDruid is offline   Reply With Quote
Old 10-25-2010, 07:10 AM   #4
PlainBill
Badcaps Veteran
 
PlainBill's Avatar
 
Join Date: Feb 2009
City & State: Phoenix, AZ
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist
Posts: 7,013
Default Re: My Viewsonic VX924 monitor died!

Follow the links in my signature for suggestions on taking and directions on attaching pictures. Take good pictures of both top and bottom of the power supply. Make them as close to 2000 x 2000 as possible. Attach them using 'Manage Attachments'. Do NOT post the picture in-line, it slows down loading the thread and irritates many of us. At this stage I don't need dozens of pictures, I need two good quality pictures, one of the top and one of the bottom.

A couple of additional points. If troubleshooting gets difficult it helps if I can quickly refer to top and bottom pictures. Most boards have an orientation - most of the component identifiers on the top, the manufacturer's name, etc are all oriented in one direction. Take the picture of the top so it is easy to reed that information. Then flip the board over sideways to take the bottom picture.

PlainBill
__________________
For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.
PlainBill is offline   Reply With Quote
Old 10-25-2010, 07:19 AM   #5
NeiltheDruid
Member
 
Join Date: Sep 2010
Posts: 42
Default Re: My Viewsonic VX924 monitor died!

Gotcha PlainBill. I'll get some pics asap.
NeiltheDruid is offline   Reply With Quote
Old 10-25-2010, 07:50 AM   #6
NeiltheDruid
Member
 
Join Date: Sep 2010
Posts: 42
Default Re: My Viewsonic VX924 monitor died!

Here you go PlainBill. Pics, top and bottom.
Attached Images
File Type: jpg DSC_0003.JPG (1.87 MB, 183 views)
File Type: jpg DSC_0005.JPG (645.8 KB, 95 views)
NeiltheDruid is offline   Reply With Quote
Old 10-25-2010, 12:09 PM   #7
retiredcaps
Badcaps Veteran
 
Join Date: Apr 2010
City & State: Canada
Posts: 8,416
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by NeiltheDruid View Post
Unfortunately, I'm still getting nothing.
Do you have a multimeter? If yes, check for 5V DC on the connector from the power board to the main/logic board.

If that is not present, carefully check for mains * 1.4 on the main filter capacitor. This is high voltage so be careful checking.

Last edited by retiredcaps; 10-25-2010 at 12:12 PM..
retiredcaps is offline   Reply With Quote
Old 10-25-2010, 01:40 PM   #8
PlainBill
Badcaps Veteran
 
PlainBill's Avatar
 
Join Date: Feb 2009
City & State: Phoenix, AZ
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist
Posts: 7,013
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by retiredcaps View Post
Do you have a multimeter? If yes, check for 5V DC on the connector from the power board to the main/logic board.

If that is not present, carefully check for mains * 1.4 on the main filter capacitor. This is high voltage so be careful checking.
Note the label on the power supply. 12V output. Otherwise, an excellent starting point.

NeiltheDruid, do you prefer to be called Neil, or Dru? Those are excellent pictures.

Check the voltage as suggested by retiredcaps, except expect 12V.
You may find no or very low output voltage, but input DC is present. In that case, look at the back of the board. You will find four transistors. Two, near the white label are Q8 and Q9, the other pair on the left side of the board are (I believe) Q10 and Q11. One pair are probably shorted.

If so, you are in for an adventure.

PlainBill
PlainBill is offline   Reply With Quote
Old 10-25-2010, 02:51 PM   #9
retiredcaps
Badcaps Veteran
 
Join Date: Apr 2010
City & State: Canada
Posts: 8,416
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by PlainBill View Post
Check the voltage as suggested by retiredcaps, except expect 12V.
Arrggh, I didn't see the markings for 12.0V earlier as I was trying to read the connector CN110.

Yes, this board clearly says 12.0V DC. So look for that instead of 5V DC.
retiredcaps is offline   Reply With Quote
Old 10-25-2010, 04:24 PM   #10
NeiltheDruid
Member
 
Join Date: Sep 2010
Posts: 42
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by retiredcaps View Post
If that is not present, carefully check for mains * 1.4 on the main filter capacitor. This is high voltage so be careful checking.
Retiredcaps, I'm a bit of a noob when it comes to working with electronics like this. When you say "* 1.4 on the main filter capacitor" what do you mean? I know what the filter cap is, but what do you mean by * 1.4?

Quote:
Originally Posted by PlainBill View Post
NeiltheDruid, do you prefer to be called Neil, or Dru? Those are excellent pictures.

Check the voltage as suggested by retiredcaps, except expect 12V.
You may find no or very low output voltage, but input DC is present. In that case, look at the back of the board. You will find four transistors. Two, near the white label are Q8 and Q9, the other pair on the left side of the board are (I believe) Q10 and Q11. One pair are probably shorted.

If so, you are in for an adventure.

PlainBill
PlainBill, Neil is fine. Just to warn you, I am a little bit of a noob. I have only fairly basic knowledge of electronics, so be gentle with me if I ask a nooby question. I'm very interested in learning from you guys though.

I checked the power-main board connector and I'm getting nothing on the dmm.

Also, when I had the board plugged in for testing, I could hear a repeating click, once a second or so. This stop a couple of seconds after the mains lead is removed.

Last edited by NeiltheDruid; 10-25-2010 at 04:29 PM..
NeiltheDruid is offline   Reply With Quote
Old 10-25-2010, 04:34 PM   #11
Wrog
Badcaps Veteran
 
Join Date: Oct 2009
City & State: Florida
Posts: 450
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by NeiltheDruid View Post
Retiredcaps, I'm a bit of a noob when it comes to working with electronics like this. When you say "* 1.4 on the main filter capacitor" what do you mean? I know what the filter cap is, but what do you mean by * 1.4?
He means 1.4 times your input line voltage. So if you are on 120V mains, you should read ~168V on the filter cap.
Wrog is offline   Reply With Quote
Old 10-25-2010, 04:44 PM   #12
PlainBill
Badcaps Veteran
 
PlainBill's Avatar
 
Join Date: Feb 2009
City & State: Phoenix, AZ
My Country: USA
Line Voltage: 120VAC 60Hz
I'm a: Hobbyist
Posts: 7,013
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by NeiltheDruid View Post
Retiredcaps, I'm a bit of a noob when it comes to working with electronics like this. When you say "* 1.4 on the main filter capacitor" what do you mean? I know what the filter cap is, but what do you mean by * 1.4?



PlainBill, Neil is fine. Just to warn you, I am a little bit of a noob. I have only fairly basic knowledge of electronics, so be gentle with me if I ask a nooby question. I'm very interested in learning from you guys though.

I checked the power-main board connector and I'm getting nothing on the dmm.
Noobs are OK, as long as they are willing to ask questions.

On retired caps request, there are several possible failures. One is a failure of the input fuse. Input voltage x 1.4 describes the DC voltage you will get across the large cap when we do not know the AC voltage in your area. For example, if you look at my profile, you will see I live in Phoenix, AZ. Our input voltage is 120 VAC. I should read 165 VDC (give or take 5 volts) across the main filter cap when the monitor is plugged in.

If you do not see any voltage, or a very low (under 5 VDC) voltage, it means there is a problem on the AC input side of the power supply - often a blown fuse. If you measure 165 VDC across the large filter cap, but do not see any output voltage either the DC - DC converter is defective, or there is a short on the 12V line.

In this case, the monitor is very similar to one which I have (and is currently kicking my butt). If the transistor pairs I mentioned earlier are shorted, the result will be a very low voltage out of the supply.

NOW, we've gotten burned on this before, and I'm not certain as to your level of nooberyness (I don't think that's a real word), so will you please attach a picture of your DMM, showing the position of the selector switch when you tried to measure the voltage.

PlainBill
PlainBill is offline   Reply With Quote
Old 10-25-2010, 04:59 PM   #13
NeiltheDruid
Member
 
Join Date: Sep 2010
Posts: 42
Default Re: My Viewsonic VX924 monitor died!

I checked the filter cap and got 333-335, which is about right since our mains is 240v.

To check the transistors I put the probes of the mm on the collector and emitter, right?

I'll get some pics of the mm tommorrow PlainBill.
NeiltheDruid is offline   Reply With Quote
Old 10-25-2010, 05:06 PM   #14
retiredcaps
Badcaps Veteran
 
Join Date: Apr 2010
City & State: Canada
Posts: 8,416
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by NeiltheDruid View Post
I checked the filter cap and got 333-335, which is about right since our mains is 240v.

To check the transistors I put the probes of the mm on the collector and emitter, right?
333 to 335V DC is correct as long as it is stable and not fluctuating.

With power off, LCD unplugged, and testing "in circuit", I like to check transistors by using ohms and testing base to collector, base to emitter, and emitter to collector.

Any reading under 20 ohms suggests a possible short. I say "possible" because components around the transistor may cause false readings.

If the readings are under 20 ohms, you will have to desolder the transistor and test them out of circuit to verify the initial ohms readings.

PS. Do you see 12V DC on the connector from the power board to the main/logic board?
retiredcaps is offline   Reply With Quote
Old 10-25-2010, 05:16 PM   #15
NeiltheDruid
Member
 
Join Date: Sep 2010
Posts: 42
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by retiredcaps View Post
PS. Do you see 12V DC on the connector from the power board to the main/logic board?
No, I didn't get any voltage. But I'm not sure I'm measuring correctly. The connector is six pins, arranged in a layout of 3x2, I don't know if this is a standard connector, but I'm not sure which pins to check.

The first set of pins is marked +12v, the second set of is marked ground and the third set is marked "AOJ". I tried the multimeter on the top +12v pin and top ground pin. Is that right?
NeiltheDruid is offline   Reply With Quote
Old 10-25-2010, 05:17 PM   #16
retiredcaps
Badcaps Veteran
 
Join Date: Apr 2010
City & State: Canada
Posts: 8,416
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by NeiltheDruid View Post
Also, when I had the board plugged in for testing, I could hear a repeating click, once a second or so. This stop a couple of seconds after the mains lead is removed.
The clicking might be the SMPS trying to start, but can't because either the startup/run cap is bad or the SMPS controller chip is bad. Or something else (to hedge my bets).

The startup/run cap is right above R112. I think it is labeled C320. The little caps can often fail without visible distress.

Once you provide the results on the 12V DC measurements on the connector, we can determine if one or both of the above is relevant or not.
retiredcaps is offline   Reply With Quote
Old 10-25-2010, 05:22 PM   #17
retiredcaps
Badcaps Veteran
 
Join Date: Apr 2010
City & State: Canada
Posts: 8,416
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by NeiltheDruid View Post
No, I didn't get any voltage. But I'm not sure I'm measuring correctly.
Here is how I do it.

Set your multimeter to 20V DC if it is not autoranging.

Put your black lead in COM and red lead in Volts.

Put your black tip probe on a screw head near the power board for GND. Put your red tip probe on the pins marked +12V.

When you say "didn't get any voltage", do you mean 0.0 V DC?
retiredcaps is offline   Reply With Quote
Old 10-25-2010, 05:26 PM   #18
retiredcaps
Badcaps Veteran
 
Join Date: Apr 2010
City & State: Canada
Posts: 8,416
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by NeiltheDruid View Post
Here you go PlainBill. Pics, top and bottom.
I don't have PlainBill's 20/20 vision, so help me out and please report the part number for chip U320 (backside).

I'm guessing this 8 pin IC is the SMPS or PWM controller. Once the part number is listed, we can then search for the datasheet and compare the stated voltages to what you are actually getting.

Also, what is the uF and voltage rating of that startup/run cap (above R112)? And do you have a replacement handy?
retiredcaps is offline   Reply With Quote
Old 10-25-2010, 05:46 PM   #19
retiredcaps
Badcaps Veteran
 
Join Date: Apr 2010
City & State: Canada
Posts: 8,416
Default Re: My Viewsonic VX924 monitor died!

Quote:
Originally Posted by NeiltheDruid View Post
Just to warn you, I am a little bit of a noob. I have only fairly basic knowledge of electronics, so be gentle with me if I ask a nooby question. I'm very interested in learning from you guys though.
Re: Noob, here are a few posts that helped me when I started to get an overall "big picture".

PlainBill's "quick walk-through on the power supply"

http://www.badcaps.net/forum/showthread.php?t=9872

PlainBill's 'divide and conquer' troubleshooting approach

http://www.badcaps.net/forum/showpos...76&postcount=8

PlainBill's Cliff's Notes on SMPS

http://www.badcaps.net/forum/showpos...6&postcount=30
retiredcaps is offline   Reply With Quote
Old 10-25-2010, 05:54 PM   #20
NeiltheDruid
Member
 
Join Date: Sep 2010
Posts: 42
Default Re: My Viewsonic VX924 monitor died!

Just back to report that there appears to be nothing coming out of the 12vdc-out power-main board connector.

Right! It's midnight, I'm off to bed, I'll pick this up in the morning.

Thanks for all the help guys.
NeiltheDruid is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 09:01 PM.


Badcaps.net Technical Forums 2003 - 2014
Powered by vBulletin ®
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.

Did you find this forum helpful?