Dead Dell 1905FP LCD monitor

[paul1149]

Hi,

I have a really nice monitor that I'd like to get working. The Dell takes in line voltage (120V AC). But nothing lights up at all, not even neon lights.

I took it apart and found three bulging capacitors. The main fuse seems to be ok. I found about 400V across the big capacitor, using an AC multimeter scale.

Other than that I don't know how to proceed. I don't have an extra CCFL on hand.

In the first picture below, the three caps are the ones in the foreground, left. They are 1- 820uF, 25V GF(M) (the tall one) and 2- 1000uF, 10V, U9A (the other two).

Please let me know if there is any other info you need. Any help is appreciated.

Blessings,
Paul

[Rtech]

Re: Dead Dell 1905FP LCD monitor

Hi,

I have a really nice monitor that I'd like to get working. The Dell takes in line voltage (120V AC). But nothing lights up at all, not even neon lights.

I took it apart and found three bulging capacitors. The main fuse seems to be ok. I found about 400V across the big capacitor, using an AC multimeter scale.

Other than that I don't know how to proceed. I don't have an extra CCFL on hand.

In the first picture below, the three caps are the ones in the foreground, left. They are 1- 820uF, 25V GF(M) (the tall one) and 2- 1000uF, 10V, U9A (the other two).

Please let me know if there is any other info you need. Any help is appreciated.

Blessings,
Paul

With 120volts Ac in measure the voltage across the big cap...BUT DC not AC...should be about 160-170 volts ???

[PlainBill]

Re: Dead Dell 1905FP LCD monitor

How about doing this the proper way? Take two pictures one of the power supply from directly overhead, and one of the back side of the power supply. For best results, they should be at least 1000 pixels on a side, but no side should be greater than 2000 pixels. Attach them using 'Manage Attachments' - below the text entry area.

PlainBill

[retiredcaps]

Re: Dead Dell 1905FP LCD monitor

I took it apart and found three bulging capacitors. The main fuse seems to be ok. I found about 400V across the big capacitor, using an AC multimeter scale.

Replace ALL your electrolytic caps on the power board, and not just the bulging ones. The largest one can be left as is because it rarely, but not never, fails.

Capacitors die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

PCBONEZ will me if I don't explain that when replacing caps, you want the same or more ripple and the same or less ESR (ohms) as per

https://www.badcaps.net/forum/showpos...47&postcount=3

Members here like Panasonic FR, FM, and FC series in that order.

PS. If you live in the USA and depending if the monitor has PFC or not, DC voltages at the big cap can reach 360 to 370V DC. As Rtech says, you are measuring DC across the big cap.

[paul1149]

Re: Dead Dell 1905FP LCD monitor

Awesome. Thanks very much to all for the input. Let's see if I can get this right.

First, I checked across the big cap and it indeed looks like about 160V DC.

Second, the new pics should be attached.

Third, I don't know what a PFC is. I don't mind replacing all the caps, but is there some way to ascertain whether the caps are the problem here?

Appreciate your time. I'll try to remove the previous thumbs.

p.

[retiredcaps]

Re: Dead Dell 1905FP LCD monitor

Third, I don't know what a PFC is.

PFC = power factor correction

http://en.wikipedia.org/wiki/Power_f...n-linear_loads

I don't mind replacing all the caps, but is there some way to ascertain whether the caps are the problem here?

Let me put it this way. Obviously bloated bad caps will NOT work.

If you are questioning our analysis, then you can measure the uF and ESR with the proper tools as I stated in post #4.

[paul1149]

Re: Dead Dell 1905FP LCD monitor

I'm not questioning your analysis, I'm trying to figure out the probability of success while feeling my way through something I've never done before. I followed PlainBill's sig links, and ended up at Mouser's. They seem to have a great selection, but what do I choose for the tolerance range? The existing caps are Samxon, 105deg C8.

Thanks,
p.

[PlainBill]

Re: Dead Dell 1905FP LCD monitor

I'm not questioning your analysis, I'm trying to figure out the probability of success while feeling my way through something I've never done before. I followed PlainBill's sig links, and ended up at Mouser's. They seem to have a great selection, but what do I choose for the tolerance range? The existing caps are Samxon, 105deg C8.

Thanks,
p.

There are three ways to handle this problem.

The first is a step by step approach. Replace the three obviously bad capacitors. If the monitor still isn't working, move on with the troubleshooting. This has the advantage of using the minimum number of components while is has the disadvantage of incurring significant shipping charges.

A second approach is to perform some rudimentary tests before ordering any parts, then order all parts that appear to be required. This takes more time initially, but improves the chances of getting a working monitor on the first try. On the bottom of the card are labels indicating the voltages out of the supply. With power on, carefully measure the voltage on each of these pins, using the pins labeled GND as a reference.

The pictures leave a lot to be desired. The easiest way to get better pictures is to turn off the flash and take the pictures near a window on a sunny day.

PlainBill

[paul1149]

Re: Dead Dell 1905FP LCD monitor

Thanks, that was helpful. I decided to stay in-house here, to order Rubycons, and to try the incremental approach.

I just checked those output voltages, and all the Ground, 12V and 5V terminals are registering fine. I'm getting nothing from the On/Off, Ready, and DIM terminals, but I'm not sure I should. I have the power board detached from everything else but the line voltage.

Lacking any contradictory indications here, I'm going to order the three bulging caps tomorrow.

I did try to take pics without flash, but they came out reddish. I didn't try with a natural light source.

p.

[FIXITNOW]

Re: Dead Dell 1905FP LCD monitor

note whem replacing the caps check
C112 it should be a 2.2uF 50v
some came out of factory with wrong part ( 22uF 50v)
replace this cap along with the otheres that have bulged

[PlainBill]

Re: Dead Dell 1905FP LCD monitor

Thanks, that was helpful. I decided to stay in-house here, to order Rubycons, and to try the incremental approach.

I just checked those output voltages, and all the Ground, 12V and 5V terminals are registering fine. I'm getting nothing from the On/Off, Ready, and DIM terminals, but I'm not sure I should. I have the power board detached from everything else but the line voltage.

Lacking any contradictory indications here, I'm going to order the three bulging caps tomorrow.

I did try to take pics without flash, but they came out reddish. I didn't try with a natural light source.

p.

The fact that you are getting those two voltages is a good sign. You are correct, the other voltages are sourced from the signal card.

PlainBill

[paul1149]

Re: Dead Dell 1905FP LCD monitor

Thanks, but I don't see a C112. On the back I see the solder points for C110 and C111, but they are under the big cap, and I don't see anything corresponding to them on the face of the board.

[paul1149]

Re: Dead Dell 1905FP LCD monitor

Gentlemen,

Observe your handiwork. I got the three caps today, and put them in this evening. The hardest thing by far was remembering how this thing went together. Next time I think I will need to put the machine together as I await the parts.

But aside from that the job went very easily. Amazingly so, actually. Many thanks for your insightful guidance. We now have another monitor at our disposal.

THANK YOU,
p.

[PlainBill]

Re: Dead Dell 1905FP LCD monitor

Gentlemen,

Observe your handiwork. I got the three caps today, and put them in this evening. The hardest thing by far was remembering how this thing went together. Next time I think I will need to put the machine together as I await the parts.

But aside from that the job went very easily. Amazingly so, actually. Many thanks for your insightful guidance. We now have another monitor at our disposal.

THANK YOU,
p.

Congratulations.

PlainBill

[retiredcaps]

Re: Dead Dell 1905FP LCD monitor

https://www.badcaps.net/forum/showpos...47&postcount=3

Sorry, correct link is (for future people)

https://www.badcaps.net/forum/showpo...47&postcount=3