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?
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My Viewsonic VX924 monitor died!
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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.
PlainBillFor 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.
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Re: My Viewsonic VX924 monitor died!
Originally posted by NeiltheDruid View PostUnfortunately, I'm still getting nothing.
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, 11:12 AM.--- begin sig file ---
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Re: My Viewsonic VX924 monitor died!
Originally posted by retiredcaps View PostDo 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.
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.
PlainBillFor 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.
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Re: My Viewsonic VX924 monitor died!
Originally posted by PlainBill View PostCheck the voltage as suggested by retiredcaps, except expect 12V.
Yes, this board clearly says 12.0V DC. So look for that instead of 5V DC.--- begin sig file ---
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Re: My Viewsonic VX924 monitor died!
Originally posted by retiredcaps View PostIf that is not present, carefully check for mains * 1.4 on the main filter capacitor. This is high voltage so be careful checking.
Originally posted by PlainBill View PostNeiltheDruid, 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
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, 03:29 PM.
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Re: My Viewsonic VX924 monitor died!
Originally posted by NeiltheDruid View PostRetiredcaps, 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?
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Re: My Viewsonic VX924 monitor died!
Originally posted by NeiltheDruid View PostRetiredcaps, 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.
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.
PlainBillFor 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.
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Re: My Viewsonic VX924 monitor died!
Originally posted by NeiltheDruid View PostI 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?
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?--- begin sig file ---
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Re: My Viewsonic VX924 monitor died!
Originally posted by retiredcaps View PostPS. Do you see 12V DC on the connector from the power board to the main/logic board?
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?
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Re: My Viewsonic VX924 monitor died!
Originally posted by NeiltheDruid View PostAlso, 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 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.--- begin sig file ---
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We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.
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Re: My Viewsonic VX924 monitor died!
Originally posted by NeiltheDruid View PostNo, I didn't get any voltage. But I'm not sure I'm measuring correctly.
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?--- begin sig file ---
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Re: My Viewsonic VX924 monitor died!
Originally posted by NeiltheDruid View PostHere you go PlainBill. Pics, top and bottom.
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?--- begin sig file ---
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Re: My Viewsonic VX924 monitor died!
Originally posted by NeiltheDruid View PostJust 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.
PlainBill's "quick walk-through on the power supply"
https://www.badcaps.net/forum/showthread.php?t=9872
PlainBill's 'divide and conquer' troubleshooting approach
https://www.badcaps.net/forum/showpo...76&postcount=8
PlainBill's Cliff's Notes on SMPS
https://www.badcaps.net/forum/showpo...6&postcount=30--- begin sig file ---
If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.
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