Dell Dimension 8400 V-Core caps

[bw1]

Just making sure here...

It's hard to see in the picture(s), but the 4th low v-core cap is starting to bulge. The originals are 820uf 4v KZV's. I've got some Chemi-con 820uf 2.5v caps that I think would be a good replacement (digikey part number 565-3057-ND).

Can someone please confirm? Thanks!

[yyonline]

Re: Dell Dimension 8400 V-Core caps

Yup. Works fine. I've done that mod a few times on some 8400s and GX280s, which has a similar motherboard.

[bw1]

Re: Dell Dimension 8400 V-Core caps

...is there a trick to this? I've given this board more heat than I've ever needed with normal recaps, and these holes will NOT clear/suck out. I've tried pushing a needle and another cap leg through as well. Yes I'm applying new solder to the back side, and everything there looks completely normal and melted, and I've tried just about every way of trying to keep the hot new solder up against the pad/hole's back side, but it won't melt through.

Does this just mean I need more heat? I've been using up to the 450*C setting on my Hakko FX888 station, and it's just not working. I just don't want to damage the board.

Help!

[yyonline]

Re: Dell Dimension 8400 V-Core caps

Yes, these boards have a lot of copper planes around the VRM caps. Lots of heat is needed. Don't worry about putting too much heat on it - the copper planes dissipate a lot of the heat away. You can safely put the iron on that area for a minute without damaging anything if you really needed to. (That advice applies only to this particular area of this particular board.)

I haven't had too much trouble with my Hakko 937 on these boards, but I use a larger 2.4mm chisel tip. You may want to try a larger tip (holds more heat).

[bw1]

Re: Dell Dimension 8400 V-Core caps

Any temp advice? How hot is too hot? And obviously, the hotter it is, the quicker my new solder degrades...

[bw1]

Re: Dell Dimension 8400 V-Core caps

Well, I've gone at this several times now, with a good heat-seal and the temp set almost as high as it goes for minutes at a time, and these holes are not clearing. Did I mention I don't normally have trouble clearing the holes?

I don't want to start picking at anything, because I know how fragile the pads are.

Is there anything else I can try? Literally, how long can I apply heat to this thing without causing other problems?

[TheLaw]

Re: Dell Dimension 8400 V-Core caps

...is there a trick to this? I've given this board more heat than I've ever needed with normal recaps, and these holes will NOT clear/suck out. I've tried pushing a needle and another cap leg through as well. Yes I'm applying new solder to the back side, and everything there looks completely normal and melted, and I've tried just about every way of trying to keep the hot new solder up against the pad/hole's back side, but it won't melt through.

Does this just mean I need more heat? I've been using up to the 450*C setting on my Hakko FX888 station, and it's just not working. I just don't want to damage the board.

Help!

If solder doesn't seem to be coming out, usually I just keep on applying fresh solder and solder wicking until it comes up. If you are using solder wick, expand it so it's not so compressed. If it's still not coming up, realy lay into it with the soldering iron...get it hot, make sure you are touching the joint and move around the soldering iron a bit. If that doesn't work, try a pump.

Heat it up. There's a lot of copper for the VRM, so it's going to take a while to heat up. Minimum wattage is around 40W with a chisel tip. In combination with old hard lead-free solder, it can definitley be a pain. Make sure to apply fresh solder to the joint and use flux-core, and/or flux.

[bw1]

Re: Dell Dimension 8400 V-Core caps

I'll try it again... but I've put huge amounts of heat into this board already.

I mean, I've tried! 1 1/2 - 2 minutes + on pretty much the highest setting on a 65w FX888, with nice new solder, a 2.4mm tip, and a solder pump on the opposite side with a good seal (plastic tip) and it's I've only managed to get a couple holes clear. I feel stupid, because this normally takes a few seconds each!

[Th3_uN1Qu3]

Re: Dell Dimension 8400 V-Core caps

Use a needle to clear the holes. Or a lead from a resistor, or whatever else fits.

[eppidrummer]

Re: Dell Dimension 8400 V-Core caps

I'll try it again... but I've put huge amounts of heat into this board already.

I mean, I've tried! 1 1/2 - 2 minutes + on pretty much the highest setting on a 65w FX888, with nice new solder, a 2.4mm tip, and a solder pump on the opposite side with a good seal (plastic tip) and it's I've only managed to get a couple holes clear. I feel stupid, because this normally takes a few seconds each!

Just an idea: This is what I use to clean the holes on every board I have done with 100% success. Mine came with an assortment of drill bits with one being the exact size of the new cap legs. I gently twist the bit through the hole. Has worked every time for me.
http://www.frantzartglass.com/index....oducts_id=1897

[inuyasha.rules]

Re: Dell Dimension 8400 V-Core caps

Please don't try using drill bits except for a last resort! Try using a hair dryer or heatgun (on low and very carefully) to preheat the board. My general rule is hot but not so hot you can't hold onto it. And I've never burnt a board yet but I also haven't ever replaced capacitors, just power jacks and stuff where there's less copper to a degree.

[Uranium-235]

Re: Dell Dimension 8400 V-Core caps

get some good flux, in combination with some 40pb/60sn solder, till the solder on the joint becomes glossy

[bw1]

Re: Dell Dimension 8400 V-Core caps

Well, I held my 2.4mm chisel tip on a nicely fluxed, filled solder hole for 4 and a half minutes of nice, glossy, 450*C, heat-transferring goodness, and after almost 5 minutes of continuous heat, the solder on the other side of the hole/board was still solid as can be.

I've never run into this before. Ready to toss the damn thing and get a board on eBay, but it's getting personal to the point that I'm not sure I can.

Any chance of using a drill bit or needle are out, regardless of whether I'd actually want to or not, because it won't soften up on the other side at all.

What's a guy to do?!?!?!?

[Th3_uN1Qu3]

Re: Dell Dimension 8400 V-Core caps

Any chance of using a drill bit or needle are out, regardless of whether I'd actually want to or not, because it won't soften up on the other side at all.

Um, well you use a drill bit in conjunction with an actual drill. Done it before. You have to make triple sure that the bit isn't large enough to drill the whole via out otherwise you ruin the board. But it sounds like the thing to do here.

[bw1]

Re: Dell Dimension 8400 V-Core caps

Veeeeeeeeery hesitant.... and I'm sure I'll have people chiming in likewise. Not completely ruling it out, but definitely an absolute last resort.

I guess my main thing here is, will more heat do the trick? Holding it longer, etc.? And I'm not sure how fragile the pads are when heated to that extent, but if you guys say to heat the hell out of it and keep trying, I guess I will, but every time I try I tell myself it's the last time.

[Th3_uN1Qu3]

Re: Dell Dimension 8400 V-Core caps

Heating it multiple times to a lower temperature will damage it more than heating it once at a really high temp. On the other hand, just try installing the new caps without clearing the holes. It's going to be slightly trickier but you're gonna be just fine. I rarely even bother to clear the holes if the new caps fit in without major headache.

Use a tip wide enough to heat both holes at the same time and just push the new cap in gently (as to not bend the leads which will have you remove it, straightening them out then trying again). It should go in easily.

[eppidrummer]

Re: Dell Dimension 8400 V-Core caps

The drill bit I am referring to is the exact size of the cap leg (smaller than the whole). The bit is used with the hand tool and not a drill and is twisted in by hand. The whole is still lined with solder when finished and has worked perfect for me on every board I have done.

Keep in mind that I do first use a solder sucker so the bit goes through most of the wholes with very little effort.

[kb1uab]

Re: Dell Dimension 8400 V-Core caps

Hi all,

I have to agree on using a finger drill with appropriate bit. Anyone who thinks they might be doing alot of rework on multi layer boards should have a set of #61-80 drill bits and a finger drill. Its easy getting the old caps out, heat and pull, then clean up the holes as best you can, then slowly drill them. The solder is softer than the copper pass through so guides it nicely. Makes fast work of a sometimes daunting task.

[eppidrummer]

Re: Dell Dimension 8400 V-Core caps

Hi all,

I have to agree on using a finger drill with appropriate bit. Anyone who thinks they might be doing alot of rework on multi layer boards should have a set of #61-80 drill bits and a finger drill. Its easy getting the old caps out, heat and pull, then clean up the holes as best you can, then slowly drill them. The solder is softer than the copper pass through so guides it nicely. Makes fast work of a sometimes daunting task.

The finger drill is pretty quick and works better than you would think. Have not damaged a hole yet with mine.

[rlbatch]

Re: Dell Dimension 8400 V-Core caps

How can I determine if the via is intact after removing the caps?