Dell 2407WFPb Monitor - Bad Cap

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

Okay so looks like my full list is Q651, F601, R670, and D652. How do I verify if the SMPS MOSFET (Q601) is bad or not before trying to power this up? Anything else I should check before ordering those 4 pieces?

And surface mounted resistors appear to be okay. I'm not seeing any real issue on the top of them it looks like.

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

If you label the pins as 1, 2, 3 on the MOSFET and then measure the resistance like this and report back what you find.

1 & 2
1 & 3
2 & 3

By the way, there is also 0.22 Ohm in that SMPS section, check and see if that one is also blown or not.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

0
591
570

And on the 0.22 Ohm SMPS resistor it looks fine, it's getting a 001, while the bad one is getting 980 about.

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

That '0' reading on 1 & 2 does not look right. I would remove the MOSFET and test it outside the board. MOSFET should read open circuit with exception if it has Source to Drain internal Diode.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

Trying again now I did get a reading when I went for the ultimate top of the post, the solder on the 2 wasn't giving me anything when attached to it. I'm attaching pictures of the meter and while I was on the board to be sure I'm not screwing this up. Again close up picture is low quality but gets where I'm testing at least across I think.

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

We are looking for short, so use the Ohm mode, when semiconductor shorted out it will be like measuring low value resistor, it will no longer act like a semiconductor (conduct in one direction only).
That is the Drain and Gate checking, definetely should not show '0'.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

At 2000K Ohms I got a reading of about 850.

Everything other than that was giving me a "1" the whole time.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

Ok so I'm about to order my bits and pieces, I'm just gathering the part #'s now to order from digikey again.

Do I need to bother with the SMPS area at all or just the parts mentioned earlier?

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

I would get the part for SMP section for future and save on shipping charge.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

Just the SMPS MOSFET?

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

Not sure how easy to get the SMPS IC.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

I don't think I'm well equip to do an IC though is the other issue. I can order everything else and give it a try. But if an IC is causing issue, there's nothing I'm going to be able to do other than just doing a bypass.

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

But you will need to repalce that IC in the PFC section, otherwise you will end up with damaged new MOSFET like the poster had done (The MOSFET went out and damaged the IC, put in new MOSFET then it is damaged by the damaged IC, hwne MOSFE goes out it will usually take out the IC that drives the MOSFET also).
What happen when the drive IC went bad is that the output either stuck LO or stuck HI (always has output voltage at the drive pin all the time) which is really bad, it will turn on the MOSFET all the time (never switch off), since the transformer has low DC resistance, the MOSTFET will blow up.

Post258:
"Things I've changed / model:

Q651: 2SK2843
Q654: MM3906
IC651: L6561D
IC601: Was NCP1200AD60 (200A6) changed for NCP1200D60 (200D6) - notice the lack of the "A", this "A" means that is a newer version of the chip, both are pin to pin compatible, and seems this circuit allows both to run (Im still not sure if these chips are fully swappable 100% of the designs)
F601: Same kind of fuse: T4AH
C605: 450v 150uF snap-in capacitor -- waiting for a replacement that will FIT into it when closed :@

I suspect that the OLD NCP1200 had a problem between the pins 5 and 6.

The "PWM" part (Except for the chip itself *sigh*) of the power supply never had a problem in my case (IE, Q601 never shorted)"

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

Would a large heat gun work for taking out IC651 then and putting a new one in? That's about the only thing I can use for that.

And would I have to worry about the IC601 all the way up by the SMPS if the .22ohm up there is fine?

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

More likely you do not have problem with the SMPS section since the MOSFET did not short out, and the resistor is OK.
When I remove surface mounted IC I add a bunch of solder to all the pin and keep moving the soldering tip around the pins (this where 40~60Watts soldering iron with wide tip comes in handy) and use a long nose plier to lift the IC off the board, if you are going to use heat gun, make sure to cover surround area not to damage other components or causes other surface mounted components to be moved.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

All I got is my cheapo radioshack iron. It isn't exactly quality but it gets the job done. I just can't personally justify a large amount of money into a station when I have so much else to pay off before that.

Heat gun will have to really be the only option, I'll try to protect everyone as much as I can but it's such a dense area that might be problematic.

[budm]

Re: Dell 2407WFPb Monitor - Bad Cap

http://s807.photobucket.com/albums/y...t=DSC00082.jpg

It is not that dense. Do you have EXACTO knife?
What you can do is to heat up the pin and slide the knife under the pin to lift up the leg one by one, no need to worry about breaking the pin. One key is that your soldeing Iron should be eleast 30Watts or more and use flux on it, you may want to add small amount of regular solder (the solder on the board is Lead free and it needs higher temp for it to melt, add 64/40 solder to it will help) to the pin to help removing the IC. There mey be adhesive that holds the IC to board also.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

Doing an IC is making me nervous but better just give it a shot while I can that's for sure.

So looks like on my order list is IC651, Q651, R670, and D652. The fuse F601 appears to be fine since I'm getting voltage at the main capacitor.

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

What's the best source for finding all these bits? Digikey is useless on a lot, as is radioshack.

I got a Fry's about an hour away. Would they for sure have all of these bits?

[Fhajad]

Re: Dell 2407WFPb Monitor - Bad Cap

Looks like I can't get any good parts supplier and Fry's doesn't have the right parts at all.

Looks like bypass is the way to go.