Dell 2407WFPb Monitor - Bad Cap

[soumen1]

Re: Dell 2407WFPb Monitor - Bad Cap

D19 won't have destroyed the hexfet; D19 is the protection zener, in place between source (ground - unless your source isn't going to ground, in which case the zener will go to ground but not source) and gateSo, if gate voltage was 2.5V, and drain 12V, then I'd stick a 3V zener in there, and not a high wattage one - you want it to fail, not cope!

I found an identical working monitor and made some progress debugging this situation (and get my monitor working again). But I did not have permission to desolder the zener on the working unit, only to measure normal voltages.

The drain of the hexfet should be at 5VDC. (Remember this is a p-channel hexfet, with drain going toward load.) This goes to an inductor which then goes to a smoothing capacitor (two 220uF in parallel) in parallel with the zener to ground. In other words, the zener is after the drain, and across 5VDC and ground. So it is very likely to be larger than 5V, and intended as a shunted load overvoltage protection device should the hexfet fail (as it did). So the hexfet was on for too long, the load saw more than zener voltage, the zener shorted out, which then made the hexfet melt. I think the designer intended it exactly this way.

I have replaced the unknown zener with a 6.8V 5W zener. I also removed the inductor and burnt hexfet, and wired up an external 5VDC supply to the top of the zener. The monitor works! (My recapped SMPS supplies 19V and 7V fine. In the SMPS board, on the 19V output line, I am planning to add a 27V 5W zener in parallel with a 30V MOV after the 5A fuse to ground.)

My only remaining question is, should I continue like this with an external 5V power supply, or should I try to replace the hexfet and inductor back in the board. It would be nice to get back to one power supply. The danger is, if the gate control circuit was damaged, the zener and hexfet will do fireworks again, and this time I may not be lucky and downstream components may fry.

Given the reports here and elsewhere, Dell should have designed the hexfet and zener as snap-in components ;-)

[2407cap]

Re: Dell 2407WFPb Monitor - Bad Cap

Hi all,

First of all, thanks for all the messages everyone has posted in this thread so far. My 2407WFP went pop the other day, and I came across this forum looking for information on how to fix it. The wealth of information in this thread has been extremely useful and encouraging.

Anyway, I've opened my monitor up to have a look around, and the only sign of damage I can find is the 450V capacitor. All the other capacitors, resistors, etc. seem fine. Apologies for the abysmal picture quality, but you can see damage on the nearest connector on the capacitor:



I was just wondering where I could source a replacement capacitor in the UK?

Would this Rubycon capacitor from RS Components fit the bill? I assume there isn't any issue with bending the connectors to position the capacitor horizontally like the original (or is there?)

Also, with regards to lifetime, the specifications on this capacitor state it's rated for 5,000 hours. Is that sufficient for this application? 5,000 hours works out at about 200 days, but I'm told the lifetime given is for the maximum operating temperature, and at lower temperatures I can expect it to last many times that. Is that correct?

Finally, does anyone have any tips on how to separate the capacitor from the white-coloured glue-like substance that's fixing it to the board? Is there some way to prise the two apart and keep the glue to fix the new capacitor in place?

Any help or advice would be hugely appreciated

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

Mark the positive and negative legs on the board, cut the legs real close to the body, then use razor blade to cut the plastic shrink tubing on the cap, then you can remove the cap body, then it will be easy to peel the tubing away from the glue. 5000 hours for 105c or 85c if you run it at that temperature rating, it will be longer at lower temp. By the way, I can see leakage on one leg of the cap, typical cap failure.

[jetadm123]

Re: Dell 2407WFPb Monitor - Bad Cap

Hi all,

First of all, thanks for all the messages everyone has posted in this thread so far. My 2407WFP went pop the other day, and I came across this forum looking for information on how to fix it. The wealth of information in this thread has been extremely useful and encouraging.

Anyway, I've opened my monitor up to have a look around, and the only sign of damage I can find is the 450V capacitor. All the other capacitors, resistors, etc. seem fine. Apologies for the abysmal picture quality, but you can see damage on the nearest connector on the capacitor:



I was just wondering where I could source a replacement capacitor in the UK?

Would this Rubycon capacitor from RS Components fit the bill? I assume there isn't any issue with bending the connectors to position the capacitor horizontally like the original (or is there?)

Also, with regards to lifetime, the specifications on this capacitor state it's rated for 5,000 hours. Is that sufficient for this application? 5,000 hours works out at about 200 days, but I'm told the lifetime given is for the maximum operating temperature, and at lower temperatures I can expect it to last many times that. Is that correct?

Finally, does anyone have any tips on how to separate the capacitor from the white-coloured glue-like substance that's fixing it to the board? Is there some way to prise the two apart and keep the glue to fix the new capacitor in place?

Any help or advice would be hugely appreciated

IIRC, when that large cap fails, it can cause other components to fail. Read this entire thread (yeah, I know it's long!) for the other components.

[dumpystig]

Re: Dell 2407WFPb Monitor - Bad Cap

Carefully prise the cap from the board and adhesive - it shouldn't take much effort. Use a blunt piece of wood - ice lolly stick is ideal - to remove adhesive from board. Then desolder the cap and remove it. It's not imperative to use more adhesive on the replacement cap, although I use a hot-glue gun.

The cap you referenced should be fine as a replacement.

[2407cap]

Re: Dell 2407WFPb Monitor - Bad Cap

Thanks everyone for the advice.

I've ordered the replacement 450V cap and a bunch of new 4A/250V fuses. I'll attempt the repair job on Wednesday and will report back with results. Given that my unit seems to have significantly less initial damage (at least based on a visual inspection) than the others I've seen posted in this thread, I'm intrigued to see how it will turn out.

In any case, if worst comes to worst, at least I'll get a fireworks display out of it!

[2407cap]

Re: Dell 2407WFPb Monitor - Bad Cap

Minor update as promised.

Swapped out the 450V cap and the 4A/250V fuse, pieced the unit together and tried powering up. Fairly certain I heard a popping noise of some sort. Otherwise, no signs of life. Opened it up again, swapped the fuse out and tried again. Definitely no noise that time, and again no sign of life.

No visible damage to any components as far as I can ascertain. Probably going to shelve this until I have more time to look at it, and just get a new monitor in the meantime...

[Jasgriff]

Re: Dell 2407WFPb Monitor - Bad Cap

Have you tested the fuse to see if it is definitely blown? If its not blown then you need to test the bridge rectifier.

[selldoor]

Re: Dell 2407WFPb Monitor - Bad Cap

Hi probably best not to recase the monitor for testing, better chance of seeing a spark
or smoke or where noise comes from - wear safety specs.
Can you post well focused pics looking straight down on your board - both sides.
Please do not post in line - use manage attachments which is in Go Advanced which is below quick reply jpg files no bigger than 2mb 2000x2000.
They should look like this https://www.badcaps.net/forum/attach...1&d=1290283049 so we can see board numbers and look for faults.

[sabretooth]

Re: Dell 2407WFPb Monitor - Bad Cap

Hi folks,

I thought I'd add to the many many posts on this particular monitor's issues. I was sitting around in the loungeroom, heard a pop from the study. I investigate about an hour later, and the monitor won't power on.

So I disassembled it and had a cursory glance at the damage. the 450v 120uF was damaged, and the fuse was also blown. I happened upon this thread, and replaced the following:
* 1 x 450v 120uF (C605)
* 5 x 35v 470uF (C711-C715)
* 2 x 50v 47uF (C606, C611)
* 1 x 25v 220uF (C703)
* 250V 4A fuse (F601)

So I thought great, it's all done. Looked away and started plugging in the power supply again, and pop! Damn. I pulled the power supply out and had a look again. On the underside of the board I found IC651's top was blown off and R670 is also burnt. I don't know if this was burnt out already. I have attached photos of how the board currently looks, with those replacements still needing to be carried out. Pardon the soldering! Also the tape is temporary, it's just there for testing. I didn't realise that the size of the replacement cap was different to the original.

So further to this, I have to replace R670 (0.22ohm, not sure of the wattage), IC651 (a L6561D PFC). Can anyone see any damage, or point out anything else that might be worth replacing?

Despite having already replaced the monitor, I'm determined to repair it!

[retiredcaps]

Re: Dell 2407WFPb Monitor - Bad Cap

Can anyone see any damage, or point out anything else that might be worth replacing?

Those are nice clear photos using manage attachments. It makes remote troubleshooting easier and eliminates a lot of playing 20 questions.

Check your power mosfet (Q651) and bridge rectifier (BD601) for shorts. These 2 are the most likely candidates for your blown fuse.

PS. selldoor is best at spotting problems on the boards through photos.

[sabretooth]

Re: Dell 2407WFPb Monitor - Bad Cap

Thanks, I made sure I read the notice, and the various signature links about guidelines for posting, etc. I work in IT and didn't want to post the equivalent of a "It doesn't work" here.

For the pixel peepers, I've uploaded larger copies of the above pictures here and here.


Also, thanks retiredcaps. I'll find out how to test those components and see what happens.

[retiredcaps]

Re: Dell 2407WFPb Monitor - Bad Cap

Also, thanks retiredcaps. I'll find out how to test those components and see what happens.

It is easy.

1) Power off and unplug your monitor. Wait 5 minutes.

2) There are 4 pins on your bridge rectifier. Number them 1, 2, 3, and 4. Measure the resistance between 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. Any resistance reading under 30 ohms suggests it is shorted. You will then have to desolder the component and retest out of circuit to verify.

3) There are 3 pins on your power mosfet. Number them 1, 2, and 3. Measure the resistance between 1-2, 1-3, and 2-3. Any resistance reading under 30 ohms suggests it is shorted. You will then have to desolder the component and retest out of circuit to verify.

[retiredcaps]

Re: Dell 2407WFPb Monitor - Bad Cap

For the pixel peepers, I've uploaded larger copies of the above pictures

I'm sure selldoor will have comments once the UK timezone comes around.

[newbie1]

Re: Dell 2407WFPb Monitor - Bad Cap

@sabretooth, you might want to checkout post #77 for the list of POSSIBLE faulty components.

On a side note, my modded (using an external power adaptor) 2407WFP is officially dead... . I still do not have the time to open it up again. Just curious, where's PB?..

[retiredcaps]

Re: Dell 2407WFPb Monitor - Bad Cap

Just curious, where's PB?..

https://www.badcaps.net/forum/showpo...&postcount=488

[sabretooth]

Re: Dell 2407WFPb Monitor - Bad Cap

Q651: 0ohm between all combinations of legs. Toast!
BD601: 600k between some legs, 1.5mil between others. So, normal?

I desoldered both to test individually and make doubly sure. Is it safe to assume that I can perform the same test on the rest of the mosfets and bridge rectifiers in the hunt for dead components?

Beyond visual inspections, is this basically how it's done if you guys had the board in your hands?

And to cut down on the number of components I'd have to test, are there components on the board that will always leave a visual indicator of failure? Say, caps that have bulged, resistors that have burnt out, etc. Also I'll make sure I test the same components from post #77 as mentioned by newbie. Newbie, what happened with your externally modded one, did it just working, make a noise, etc? I was thinking of using that mod as my next port of call should I be unable to properly diagnose this board. I'd be interested to see what happened when you get the time to check it out.

Thanks.

[retiredcaps]

Re: Dell 2407WFPb Monitor - Bad Cap

Q651: 0ohm between all combinations of legs. Toast!

Absolutely shorted.

BD601: 600k between some legs, 1.5mil between others. So, normal?

Not shorted so likely good.

I desoldered both to test individually and make doubly sure. Is it safe to assume that I can perform the same test on the rest of the mosfets and bridge rectifiers in the hunt for dead components?

I always test components in circuit first. If the readings are suspicious, then I desolder to verify.

You can check the rest of your mosfets (pcb designation "Q") and diodes (pcb designation "D") in circuit. Definitely check D652 and D655 as it might have sustained collateral damage from Q651. A good diode should read 0.4V to 0.7V in one direction and 0L in the other. If you get a reading in both directions, you will have to desolder one leg and retest to verify.

There is only one bridge rectifier in your power supply.

More about testing these components are explained starting with post #19 at

https://www.badcaps.net/forum/showthread.php?t=10419

Beyond visual inspections, is this basically how it's done if you guys had the board in your hands?

After you learn a bit more, you will be able to narrow down likely culprits.

And to cut down on the number of components I'd have to test, are there components on the board that will always leave a visual indicator of failure?

Some electronics devices are infamous for having a certain problem. For example, older Benq lcd power/inverter boards have shoddy soldering which leads to certain problems. So knowing the history helps narrow down which components are likely bad.

The Hanns-G 28 inch monitors run temperature hot and heat kills caps so we see a lot of people with this monitor having all sorts of problems due to bad, but not bulged, caps.

[newbie1]

Re: Dell 2407WFPb Monitor - Bad Cap

Newbie, what happened with your externally modded one, did it just working, make a noise, etc? I was thinking of using that mod as my next port of call should I be unable to properly diagnose this board. I'd be interested to see what happened when you get the time to check it out.

Thanks.

I got it up and running using the power adaptor mod for a few months. Suddenly, it just went dead. No power led light up even though i measured and confirmed that the power adaptor is fine. Maybe the rest of the guys with the same mod have better luck than me. What i would suggest for you is to perform the current limiter test using light bulb after replacing the faulty parts. This will help verify whether there are more faulty parts on the board that are shorting it.

https://www.badcaps.net/forum/showpo...&postcount=488

Thanks retired. Hope he is having a 'blast' during his well deserved break..

[sabretooth]

Re: Dell 2407WFPb Monitor - Bad Cap

A summary so far. The components tested in this list have either been identified by myself as failed, suggested by retiredcaps, or suggested by post #77.

Diodes were tested by ensuring continuity in one direction only.

Casualties:

• R670
• Q651
• F601
• C605
• IC651

Tested OK:

• BD601
• ZD601
• D652
• D655

Checked, but not sure of the result I got:

• R669 - 15k ohm, but post #77 says this should be 1k.
• IC601 - Doesn't seem shorted. Varying resistances between pin pairs. I'm guessing this is OK as I suspect a failure would mean no resistance between pairs/visible damage like IC651, or no continuity at all.

Any comments?