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Old 01-17-2011, 12:13 PM   #41
retiredcaps
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by Neobyte View Post
Yes it should be 5V. Every pin shows close to zero voltage (maybe it's zero then). <0,1V anyways.
When you recapped the monitor, did you recap the little cap just above the word CAUTION?

That little cap plays an important role in the startup of the SMPS which generates the secondary voltages (i.e. 5V DC).

edit: Also, what is the DC voltage across that little cap. Put your black probe on the negative and red probe on the positive leg of the cap. Is it a steady or fluctuating voltage?
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Old 01-17-2011, 12:32 PM   #42
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by retiredcaps View Post
When you recapped the monitor, did you recap the little cap just above the word CAUTION?

That little cap plays an important role in the startup of the SMPS which generates the secondary voltages (i.e. 5V DC).

edit: Also, what is the DC voltage across that little cap. Put your black probe on the negative and red probe on the positive leg of the cap. Is it a steady or fluctuating voltage?
Yes I was aware of that cap's role and I also changed that one. It was 22uF (50V). I measured that one also and got steady 10 V (DC). What's next?
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Old 01-17-2011, 01:05 PM   #43
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by Neobyte View Post
What's next?
1) On the back of the board there should be a multi legged IC. It is the SMPS controller chip. Read the part number and find its datasheet. Post the URL here so it is available for everyone to see.

2) Just left of the CN301 is a dual diode or Schottky diode mounted on the heatsink.

a) with power off and lcd unplugged, use the diode test on your multimeter. pin 2 is the middle pin. You can do these measurements "in circuit".

b) Put your red probe on pin 1, black on pin 2. Report measurement.

c) Put your red probe on pin 2, black on pin 1. Report measurement.

d) Put your red probe on pin 3, black on pin 2. Report measurement.

e) Put your red probe on pin 2, black on pin 3. Report measurement.

3) Now put your multimeter to 20V DC. On the same dual diode as above, with power on and lcd plugged in, put your black probe on a ground screw and your red probe on pin 2. Report voltage reading.

For test #2, we are checking to make sure the diode is not shorted out. Two readings should be around 0.1 to 0.3 V. The other two should read "1" or "0L" depending on your multimeter.

For test #3, we are seeing if there is voltage on the dual diode. For test #3, I believe we will see 0V DC, but I just want confirmation.
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Old 01-17-2011, 01:56 PM   #44
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by retiredcaps View Post
1) On the back of the board there should be a multi legged IC. It is the SMPS controller chip. Read the part number and find its datasheet. Post the URL here so it is available for everyone to see.

2) Just left of the CN301 is a dual diode or Schottky diode mounted on the heatsink.

a) with power off and lcd unplugged, use the diode test on your multimeter. pin 2 is the middle pin. You can do these measurements "in circuit".

b) Put your red probe on pin 1, black on pin 2. Report measurement.

c) Put your red probe on pin 2, black on pin 1. Report measurement.

d) Put your red probe on pin 3, black on pin 2. Report measurement.

e) Put your red probe on pin 2, black on pin 3. Report measurement.

3) Now put your multimeter to 20V DC. On the same dual diode as above, with power on and lcd plugged in, put your black probe on a ground screw and your red probe on pin 2. Report voltage reading.

For test #2, we are checking to make sure the diode is not shorted out. Two readings should be around 0.1 to 0.3 V. The other two should read "1" or "0L" depending on your multimeter.

For test #3, we are seeing if there is voltage on the dual diode. For test #3, I believe we will see 0V DC, but I just want confirmation.
The IC on the back is BIT3715 and the datasheet is here:
HTML Code:
http://monitor.espec.ws//files/bit3715_633.pdf
b 800 c I d 800 (is it 800mV or what?)
Test #3 was 0V as you guessed.
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Old 01-17-2011, 03:09 PM   #45
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by Neobyte View Post
b 800 c I d 800 (is it 800mV or what?)
It is 800mV. I don't understand what you mean by be "b c I d"? You should have 4 readings following the instructions posted earlier.

Last edited by retiredcaps; 01-17-2011 at 03:24 PM.. Reason: edit: saw PlainBill's post about wrong part number
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Old 01-17-2011, 03:18 PM   #46
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by Neobyte View Post
The IC on the back is BIT3715 and the datasheet is here:
HTML Code:
http://monitor.espec.ws//files/bit3715_633.pdf
b 800 c I d 800 (is it 800mV or what?)
Test #3 was 0V as you guessed.
Wrong IC. That's the inverter controller. There should be an 8 pin IC. The 10 volts across the small cap is significant. That is below the usual start threshold for an SMPS controller.

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Old 01-17-2011, 03:31 PM   #47
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by PlainBill View Post
Wrong IC.
Doh, I should have spotted that earlier. It seems like my multitasking skills are dwindling.

What brand and series did you use for a replacement cap (the little one)? Is it a new cap (we have some people reuse caps)?
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Old 01-18-2011, 02:55 AM   #48
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by retiredcaps View Post
Doh, I should have spotted that earlier. It seems like my multitasking skills are dwindling.

What brand and series did you use for a replacement cap (the little one)? Is it a new cap (we have some people reuse caps)?
Ok I got a pic of the right controller. In the same pic you can see the soldering of that small cap. It was difficult place and I have suspicions. Maybe I should try to resolder that one. Closest datasheet I could find was this:
http://pdf1.alldatasheet.com/datashe...TEA1530AP.html

I didn't reuse any caps, but my supplier had wide variety of brands. So the small cap is SME(?) and there are also two other SMEs. One rubycon and one unknown. I'm not sure which series.

To previous msg, sorry I meant: b I / c 800 / d I / e 800
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Old 01-18-2011, 03:39 AM   #49
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

Quote:
Originally Posted by Neobyte View Post
Ok I got a pic of the right controller. In the same pic you can see the soldering of that small cap. It was difficult place and I have suspicions. Maybe I should try to resolder that one. Closest datasheet I could find was this:
http://pdf1.alldatasheet.com/datashe...TEA1530AP.html

I didn't reuse any caps, but my supplier had wide variety of brands. So the small cap is SME(?) and there are also two other SMEs. One rubycon and one unknown. I'm not sure which series.

To previous msg, sorry I meant: b I / c 800 / d I / e 800
Mixing brands is not a problem, using the wrong series (ESR) of cap is a problem.

Carefully!!! measure the voltage between the - lead of the large cap and pin 1 of the TEA1530AP. (This is also the voltage across the small cap you replaced). The minimum start-up voltage of the TEA1530AP is 10.3 volts. If the voltage is steady and below that, replace the TEA1530AP. If the voltage appears to be fluctuating, or if you can hear a ticking sound every few seconds, you have a short, reversed capacitor, or bad solder joint somewhere.

That soldering job will not win any workmanship awards, but is not the source of your problem. I would trim leads shorter, however.

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Old 01-18-2011, 06:39 AM   #50
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by PlainBill View Post
Mixing brands is not a problem, using the wrong series (ESR) of cap is a problem.

Carefully!!! measure the voltage between the - lead of the large cap and pin 1 of the TEA1530AP. (This is also the voltage across the small cap you replaced). The minimum start-up voltage of the TEA1530AP is 10.3 volts. If the voltage is steady and below that, replace the TEA1530AP. If the voltage appears to be fluctuating, or if you can hear a ticking sound every few seconds, you have a short, reversed capacitor, or bad solder joint somewhere.

That soldering job will not win any workmanship awards, but is not the source of your problem. I would trim leads shorter, however.
I understand. It seems that the small cap was united chemi-con and the series is SME. I found this http://www.chemi-con.com/files/SMESME%20Series.pdf datasheet. There's some max 22uF (50V) ESR values measured in 120Hz. So if the ESR is too high it causes the low voltage?

I got the same steady 10,03V from that measurement also. So it is below 10,3V. I may try to change that cap someday, if I just could find better ones somewhere. Thanks also for the soldering feedback, appreciated!
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Old 01-18-2011, 08:21 AM   #51
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

Quote:
if I just could find better ones somewhere.
As you're a fellow Finn, I'd recommend the Digi-Key group order service run by VV-soft
http://www.vvsoft.fi/dk/
Since the company is located at Tampere, you won't have to pay any shipping costs (if you fetch the stuff from their office). Next deadline for group order is 24.1. I've had 4 orders delivered by mail and it works like a charm.

Also, for some electronics discussion in Finnish, you might want to check out Muropaketti's electronics forum http://murobbs.plaza.fi/elektroniikka/
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Old 01-18-2011, 09:55 AM   #52
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

Quote:
Originally Posted by Neobyte View Post
I understand. It seems that the small cap was united chemi-con and the series is SME. I found this http://www.chemi-con.com/files/SMESME%20Series.pdf datasheet. There's some max 22uF (50V) ESR values measured in 120Hz. So if the ESR is too high it causes the low voltage?

I got the same steady 10,03V from that measurement also. So it is below 10,3V. I may try to change that cap someday, if I just could find better ones somewhere. Thanks also for the soldering feedback, appreciated!
The symptoms point to a failure of the TEA1530AP.

Here is a rundown of the normal startup process. Notice pin 8 of the TEA1530AP is tied to the high side of the main filter cap. When AC power is applied it starts charging that cap through a constant current source. When the voltage across the cap reaches 11V it starts driving the gate of the main power FET through pin 6. That generates voltages in the secondary windings, which are rectified to power the inverter and signal (logic) card. It also generates a voltage in the tertiary winding, which provides power to the TEA1530AP via a diode.

There are three failure modes.

1. A shorted diode on an output, or an excessive load on one output. The power supply cannot produce enough power to produce run power via the tertiary winding. The symptom is a quiet ticking sound, and pulsing voltage at pin 1 of the TEA1530AP. The outputs will be dead.

2. The capacitor is open. The TEA1530AP cannot run long enough to provide run power at pin 1. The symptoms are a quiet ticking sound, pulsing at the power supply outputs, and at pin 1.

3. A failure in the TEA1530AP. The capacitor never charges to the point the SMPS controller will start. The symptoms are no output voltage, no ticking sound, and a steady voltage at pin 1 below 10.3 volts.

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Old 01-18-2011, 09:56 AM   #53
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by jpartanen View Post
As you're a fellow Finn, I'd recommend the Digi-Key group order service run by VV-soft
http://www.vvsoft.fi/dk/
Since the company is located at Tampere, you won't have to pay any shipping costs (if you fetch the stuff from their office). Next deadline for group order is 24.1. I've had 4 orders delivered by mail and it works like a charm.
Whoa didn't know that, thanks a lot for the info!

Quote:
Also, for some electronics discussion in Finnish, you might want to check out Muropaketti's electronics forum.
Yes I've been reading that forum also
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Old 01-18-2011, 10:49 AM   #54
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

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Originally Posted by Neobyte View Post
Ok I got a pic of the right controller.
Excellent photo.

Quote:
So the small cap is SME(?) and there are also two other SMEs.
Okay, since you can get a group buy with free shipping, I suggest the Panasonic FM 22uF 50V at digikey.com. The FC version will also work fine.

Quote:
To previous msg, sorry I meant: b I / c 800 / d I / e 800
For those reading this, the non shorthand version of this is

base - collector => infinity/ 800mV
drain - emitter => infinity/800mV
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Old 01-18-2011, 12:24 PM   #55
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

Just remembered that the you can't get all components offered in the States here in Finland. So use digikey.fi instead of .com just to be on the safe side.
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Old 01-20-2011, 05:48 PM   #56
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Smile Re: 2 Viewsonic VX1940W buzzing and no signal

I got all the parts in (most from Digi-Key, a couple from Mouser because Digi-Key backordered them), and installed them on the inverter board.

As promised, a pic of the repaired board. ...as a bonus, a pic of the repaired monitor, moments after putting it all back together.
Attached Images
File Type: jpg S3010024.jpg (425.0 KB, 93 views)
File Type: jpg S3010025.jpg (232.6 KB, 64 views)
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Old 02-01-2011, 12:02 PM   #57
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

Thank you very much.
Repaired Viewsonic X1940W LCD monitors.
Replaced C1, C302, C305. Capacitors CapXon "bulging" after 1 year MAINTENANCE monitor.

Thanks for the detailed issledorvanie problem.
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Old 02-05-2011, 06:04 PM   #58
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

Can I also add my thanks for all the detailed information posted above.
In my case I replaced only C1 and C302 (both bulging). This fixed the problem.

Saved me from replacing my monitor!
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Old 05-03-2012, 01:04 PM   #59
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

I also thank you all so much for the help. Juste replaced the five caps (following others topics here on the VX1962WM) and it's working like a charm. Even for a non electronic-savvy guy as myself (my last solder was like 10 years ago in high school), everything went perfectly fine.

Big thanks !
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Old 05-03-2012, 02:03 PM   #60
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Default Re: 2 Viewsonic VX1940W buzzing and no signal

Well done Xanator thanks for letting us know.
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