Need help DCLCD 19" LCD Monitor - I already replaced caps

[retiredcaps]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I can change them both out. The big and the little. The pulsing voltage looks to me like a cap building then leaking down over and over.

I recommend changing them one at a time so we know root cause. Make sure to use low quality ESR caps like Rubycon MCZ, Panasonic FM/FC, or United Chemi-con.

[jetadm123]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

SG3842GS
ADAX87140421E

Need to leave work until tomorrow.
Thanks for working with me on this. I will pull the caps tomorrow and get then replaced asap and test. If you have anymore checks for me to try, I will be checking the board.

What about the white paste that is on the caps to hold them to the board. Will I need to replace that?

The white adhesive you're talking about is only used during the assembly process and does not need to be replaced.

[DJM_PHX]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

The small cap should be connected near a SOIC-8 PWM chip on the bottom of the board. Can you read off the part number of that chip?

SG3842GS
ADAX87140421E

Need to leave work until tomorrow.
Thanks for working with me on this. I will pull the caps tomorrow and get then replaced asap and test. If you have anymore checks for me to try, I will be checking the board.

What about the white paste that is on the caps to hold them to the board. Will I need to replace that?

[jetadm123]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I can change them both out. The big and the little. The pulsing voltage looks to me like a cap building then leaking down over and over. I usually only ramp them until breakdown on our structures on wafers.

The small cap should be connected near a SOIC-8 PWM chip on the bottom of the board. Can you read off the part number of that chip?

[retiredcaps]

Re: High Main Cap Voltage

This thread reminded me of an X20G Scepter monitor that I last summer read 375VDC on the main cap...yanked the plug and put it aside.
So for future reference, what if a main cap is quite elevated over the 160VDC level for LCD power supplies?

I believe the X20 has a PFC to get 375V DC and this one doesn't. So 160V DC is correct for this monitor.

[DJM_PHX]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

A few questions:

1) Looks like the power supply is not running by the looks of the outputs at the wiring harness. When you took the voltage readings, was everything hooked up? Some power supplies require a load before they will start.

Everyting is/was connected. Double checked all of them.

2) I circled a connector on your photo. Was it connected to anything?

Nothing was connected there.

3) The small cap that's next to the large cap. Try to measure the voltage across it. Please report what you see. Be careful of the high voltage cap next to it.

11V-14V varies like the rest

4) If you can post a photo of the entire bottom of the board, it would be helpful.

I returned the dept camera. I can get it again tomorrow.

Also the heat sink. I had the black on the PCB screw connector (just right of the optoisolator) and touched the red to the sink. I would think I should not register anything, but I do. I also tried it with the black lead connected to the green ground wire on the screen frame. -80+V.

The fuse is good.
REV 3 not J on the board.

I can change them both out. The big and the little. The pulsing voltage looks to me like a cap building then leaking down over and over. I usually only ramp them until breakdown on our structures on wafers.

[kingofcoins]

Re: High Main Cap Voltage

This thread reminded me of an X20G Scepter monitor that I last summer read 375VDC on the main cap...yanked the plug and put it aside.
So for future reference, what if a main cap is quite elevated over the 160VDC level for LCD power supplies? In which ways should the repair tech proceed?

[retiredcaps]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I see the same voltage pulsing on what looks like a fuse (red). I also see a pulsing -85V on the metal piece framed in green. Isn't that a heat sink?

F on the pcb denotes a fuse. A good fuse should measure less than 1.0 ohms (with power off and lcd unplugged).

The metal piece is a heatsink. -85V again means you have the wrong GND point.

Change out that little cap first and then we can proceed.

[jetadm123]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

1) Blk 0-0.03V
2) Brn 0V
3) Red 0V
4) Org 0V
5) Yel 0-0.04V
6) Red 0-0.04V
7) Blk 0-0.04V
8) Yel 0V
9) Gry 3.5V
10) Wht ~0.002V
11) Blk 0V
12) Brn 0V
13) MT
14) Red 0-0.04V
15) Org 0-0.04V


The large cap measured 172V-174V. Varying like the other voltages above.


Is the secondary voltages you are talking about the 2V variation?



I will have to try to borrow a dept camera to do this. I will try for today.
I have gone over the other pic and it is like mine, but I will follow up with the pic.
Number off of the board: LM004 Rev J 12/01/2003

A few questions:

1) Looks like the power supply is not running by the looks of the outputs at the wiring harness. When you took the voltage readings, was everything hooked up? Some power supplies require a load before they will start.

2) I circled a connector on your photo. Was it connected to anything?

3) The small cap that's next to the large cap. Try to measure the voltage across it. Please report what you see. Be careful of the high voltage cap next to it.

4) If you can post a photo of the entire bottom of the board, it would be helpful.

[retiredcaps]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

1) Blk 0-0.03V
2) Brn 0V
3) Red 0V
4) Org 0V
5) Yel 0-0.04V
6) Red 0-0.04V
7) Blk 0-0.04V
8) Yel 0V
9) Gry 3.5V
10) Wht ~0.002V
11) Blk 0V
12) Brn 0V
13) MT
14) Red 0-0.04V
15) Org 0-0.04V

Okay, a lot of voltages are zero for GND.

The large cap measured 172V-174V. Varying like the other voltages above.

If you are getting a fluctuating voltage at the big cap, this could be a sign that the big cap is bad. I noticed this board was made in Dec 2003 which means the caps are 7 years old. Let's assume the big cap is good for now, but note it for later.

The little cap that I referred to earlier comes into play after the big main cap.

Is the secondary voltages you are talking about the 2V variation?

The main (or primary) voltage is what comes from your wall. The term secondary refers to voltages that are not main. The LCD requires many voltages to operate the electronics. Hence the need for secondary voltages.

Since we are not seeing many secondary voltages in your measurement above, let's change out just small cap lying on its side next to the big cap. Normally, we recommend that you change all the electrolytic capacitors, but I'm trying to help you find root cause first. So by changing the little one, we might find that as root cause.

[DJM_PHX]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I see the same voltage pulsing on what looks like a fuse (red). I also see a pulsing -85V on the metal piece framed in green. Isn't that a heat sink?

[DJM_PHX]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

This is the best I can do today. The better dept camera is not available. I think just about everybody is out for Xmas.

[DJM_PHX]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

1) If the power LED does not come on at all, measure the all the pins on the connector (just right of the optoisolator). Use a ground screw for the black probe. The red probe goes to each pin. Put your multimeter on 20V DC. List, measure, and record each pin. You are looking for DC voltage. At minimum, you should see 5V DC on one of the pins.

1) Blk 0-0.03V
2) Brn 0V
3) Red 0V
4) Org 0V
5) Yel 0-0.04V
6) Red 0-0.04V
7) Blk 0-0.04V
8) Yel 0V
9) Gry 3.5V
10) Wht ~0.002V
11) Blk 0V
12) Brn 0V
13) MT
14) Red 0-0.04V
15) Org 0-0.04V

2) You are using the incorrect GND if you are getting negative voltages. To test the large cap, put your multimeter on 200V DC (if manual). Put your black probe on the negative leg and red probe on the positive leg. If you have 120V main voltage, the big cap should read 120 x 1.414 or roughly 160V to 165V DC. It should be a stable voltage. CAREFUL, this is high voltage.

The large cap measured 172V-174V. Varying like the other voltages above.

3) The pulsing voltage is a clue. The small cap lying on its side just right of the big cap could be bad without bloating. That cap is critical to the SMPS startup process. So if you do not see any secondary voltages from #1, this small cap could be the culprit.

Is the secondary voltages you are talking about the 2V variation?

4) Can we clear and focused picture of YOUR board? Reusing other people's pictures (especially without telling us) doesn't help us diagnose YOUR problem. Your board could have unique characteristics not shown in someone else's photo. It is not uncommon for manufacturers to make changes on their boards. Also try to get the resolution as close to 2000x2000 as possible.

I will have to try to borrow a dept camera to do this. I will try for today.
I have gone over the other pic and it is like mine, but I will follow up with the pic.
Number off of the board: LM004 Rev J 12/01/2003

[EGuevarae]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

3) The pulsing voltage is a clue. The small cap lying on its side just right of the big cap could be bad without bloating. That cap is critical to the SMPS startup process. So if you do not see any secondary voltages from #1, this small cap could be the culprit.

I agree.That little guy has given me some trouble in the past.And is ofter overlooked.

[retiredcaps]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

The LED was a solid blue before then would start blinking, now it does not come on at all.

Also, why do I see a -80V on the top of the large cap and a -84V and a -85V on the leads? All voltage measurements are pulsing just as I see it from the opto isolator.

1) If the power LED does not come on at all, measure the all the pins on the connector (just right of the optoisolator). Use a ground screw for the black probe. The red probe goes to each pin. Put your multimeter on 20V DC. List, measure, and record each pin. You are looking for DC voltage. At minimum, you should see 5V DC on one of the pins.

2) You are using the incorrect GND if you are getting negative voltages. To test the large cap, put your multimeter on 200V DC (if manual). Put your black probe on the negative leg and red probe on the positive leg. If you have 120V main voltage, the big cap should read 120 x 1.414 or roughly 160V to 165V DC. It should be a stable voltage. CAREFUL, this is high voltage.

3) The pulsing voltage is a clue. The small cap lying on its side just right of the big cap could be bad without bloating. That cap is critical to the SMPS startup process. So if you do not see any secondary voltages from #1, this small cap could be the culprit.

4) Can we clear and focused picture of YOUR board? Reusing other people's pictures (especially without telling us) doesn't help us diagnose YOUR problem. Your board could have unique characteristics not shown in someone else's photo. It is not uncommon for manufacturers to make changes on their boards. Also try to get the resolution as close to 2000x2000 as possible.

[DJM_PHX]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

If you hookup a computer displaying your favorite wallpaper, do you still see it by shining a flashlight onto the screen? Also, does the power LED stay green/blue?

I used an LED flashlight and see nothing. Tried this before.

The LED was a solid blue before then would start blinking, now it does not come on at all.

Also, why do I see a -80V on the top of the large cap and a -84V and a -85V on the leads? All voltage measurements are pulsing just as I see it from the opto isolator.

Depending on how you answer the above question, we can suggest test points on the board. The item you have circled looks like the opto isolator.

thanks

[retiredcaps]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

Ok, I have the same issue. Turns on for a second, then goes out.

If you hookup a computer displaying your favorite wallpaper, do you still see it by shining a flashlight onto the screen? Also, does the power LED stay green/blue?

I put a DMM on several points on the board.

Depending on how you answer the above question, we can suggest test points on the board. The item you have circled looks like the opto isolator.

[DJM_PHX]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

Ok, I have the same issue. Turns on for a second, then goes out. I put a DMM on several points on the board. But what seemed strange was the right side terminals of the circled piece (AC connection to the left) kept flashing my Fluke from 4.xxV - 5.xxV, then to OL and back. On the DMM on the left I was getting -80 Volts. Is the where the AC is suppose to be converted to DCV? If so, this could be the failed part. What type of part is it? #4G P721F 4GR

[EGuevarae]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

... didn't bother replacing all of them, just these 2 popped(CapXon, 16V 1000uF). .....

I hope you don't bother reopening the unit soon either.There's a good reason for changing ALL the caps except the bigger one, and with the correct caps ...

[number22]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I had problem with my similar DCLCD 19" monitor, anyway, I scavenged 2 capacitors (TEC, 16V, 1000uF) from a bad power supplies, test them out, and the monitor is work like new, the color is vivid.

Symptoms:Monitor began color shifting a while back(a year ago), greenish mostly, I didn't bother fix it, until it die out on me yesterday, open her up, find bad brand capacitors all in, didn't bother replacing all of them, just these 2 popped(CapXon, 16V 1000uF). anyway, I have been using it for like about 4 years. now it is like new, just want to share my experience, hoping it will help other. Great site though.