HP dc7800

[Telkwa]

IT dept. sold me a half dozen dc7800's, all with at least one bad cap.

I've read a couple of posts on here where people said get rid of all OST caps. That would be a big project, because HP used a bunch of 'em on these boards.

5 of 6 boards have a short, fat OST 6.3v 1500 uf cap next to the memory sticks (1st attachment) and they're all swelling. The 6th board has a black & gold cap instead (Rubicon) and that one looks OK.

There are some 10v 1K uf OST's that are swelling. 2nd attachment.

There are some taller, thinner 6.3v 1500uf OST's in other spots that are starting to bulge. 3rd attachment.

I don't have the right tools for this, but maybe I can get some help. My first question would be about those OST's. Are they that cheap of a brand that you would consider replacing all? Or just the ones that are visibly sick?

OK, I have light blue OST RLA's and some midnite blue with gold stripe OST RLX's.

Oh, hey, I forgot to mention - I marked the bulging ones with a Sharpie. That's why you see black on top of some of the caps.

[larrymoencurly]

Re: HP dc7800

3-4 of my last 5 motherboard failures happened when OST caps popped around the DIMM sockets.

[Telkwa]

Re: HP dc7800

Kinda looks like a pattern. My 40W Weller isn't quite strong enough to get the caps out, but maybe the guys in our electrical shop can help me.

I was kind of overstating things when I said that HP used a bunch of them. There are at most about a dozen OST's on any one board if you include both RLA and RLX. Some of the boards only have one OST, the one bulging near the DIMM sockets. Others have 3 or 4 OST's.

All the boards have 4 Sanyo's in the exact same spots. Sanyo is supposed to be pretty good, right?

[Telkwa]

Re: HP dc7800

In the first post I mentioned that all but one of the boards had bad OST's right next to the DIMM sockets. So, I thought, let's get the exact model from the one board that didn't fail. The attached pictures show the cap that replaces the OST RLA on the one board out of six. The black color made it hard to get a decent pic. The black/gold looks to this newbie like a Rubycon but it's such a stubby capacitor that all I can see for an identifier is that "W" or "M" inside the box. Anyone know what this is? AFAICT they're 10mm by about 12mm. Very short because it sets almost below the DIMM socket retainer lever. I could get away with a few mm taller...

If someone would just please tell me exactly what to buy

I poked around in the Good Caps thread - that little "M" inside the box is Panasonic?!? OK, wait, the M stands for Matsushita. It appears FL is not common?

[Telkwa]

Re: HP dc7800

I came across another website about cap replacement. They mentioned snipping off the old cap leads as close to the board as possible to get better heat transfer. It worked! All the bulging caps are out and I placed an order with Topcat. Bought the Nichicons that appear to be the correct replacements.

More expensive than some of the alternatives, but I trust Badcaps.net.

[Telkwa]

Re: HP dc7800

I needed to clean the holes. My wife let me rummage through her sewing gear. I assume the pins I used were SS - the solder either didn't stick, or flaked right off. Seemed like the pins were either too thin, or the next size up was too fat. I was worried about damaging the hole with the fatter ones. Woulda bought some dental picks if I'd planned ahead for this job. Readily available online and cheap. I'm sure the cheap ones are knock-offs of the real ones...

[momaka]

Re: HP dc7800

OK, I have light blue OST RLA's and some midnite blue with gold stripe OST RLX's.

Both are trash series (as is Ost in general) that should be replaced regardless of their state, especially in small "mini-oven" SFF and USFF desktops.

All the boards have 4 Sanyo's in the exact same spots. Sanyo is supposed to be pretty good, right?

Yes, Sanyo caps are very good indeed.

I poked around in the Good Caps thread - that little "M" inside the box is Panasonic?!? OK, wait, the M stands for Matsushita. It appears FL is not common?

Yes, the [M] loo in a box stands for Matsushita, aka Panasonic. FL are actually used quite often on motherboards so they are not uncommon. However, Panasonic sells FL series caps only to board manufacturers, so that's why you won't see them for sale in any store.

[Telkwa]

Re: HP dc7800

OK, thanks, the Good Caps thread mentioned several Matsushita caps (FE & FZ I think?), but FL was only mentioned once so I assumed it was rare.

In 2005 I built my first PC from all new parts. I chose an ASUS P5GDCV board because I thought ASUS made good stuff. The board currently sets on a shelf. I picked it up yesterday and was surprised to see that it's infested with OST caps!

I might go back at a later date and replace all the OST's on these dc7800 boards, but I think for right now I need to reassemble and see if any of them work.

[Anndy]

Re: HP dc7800

Kinda looks like a pattern. My 40W Weller isn't quite strong enough to get the caps out

Is it really? or maybe your just not doing it right!
Believe it or not, I've done it before (multiple times) with a cheapo 30W iron!
Here's what I learned, a lot of motherboards and other circuit boards from recent years are ROHS complaint, and this basically means that they use lead-free solder. Now this kind of solder melts at much higher temperatures than ordinary one. When I first started doing these kind of stuff, I too couldn't get the solder to melt and considered buying a higher-wattage iron, but I decided to do some research first and found a tip that was extremely useful! you should always add new solder to the joint before attempting to de-solder it, this has worked for me many times! I don't know why it works, but it just does! so I strongly recommend you try this before buying a 75-80W soldering iron.
Also, removing the capacitor and then heating the solder from the other side to insert it's replacement is a very tedious task and I wouldn't recommend going this way.
What you should do instead is use solder wick (also called desoldering braid) to remove as much solder as you can, then if it's loose just remove the capacitor, if it's not then heat up the solder and then remove it (better not touch it with your bare fingers, use a soft-cloth like the one that comes with sunglasses, that's what I do) anyways, if you removed most of the solder with the wick but the hole is still not opened, there are a number of different ways to open it, such as heating it from one side and sticking a steel dental pick from the other, using a desoldering iron or desoldering bulb. This is the proper way to do it, once you get the holes all free, you just insert the new caps in, put a little solder from the other end then cut the unneeded portion of the leads when your done. I generally put the new capacitor in, hold it and then put the motherboard upside down in order to do the soldering work, another trick I learned is that if the capacitor is too loose, just stick it from the other side with electric tape, then solder it and remove the tape when done! Oh, and very important, you have to watch the polarity when inserting a new capacitor! generally speaking, there should be a minus or white area on the PCB which indicates its the minus, but it'd be easier to just take pen and paper, have a look at the capacitor and write it down before you go ahead with it, or use a sharpie to mark the minus side. I hope you learned a lot from this and good luck to you!

[Telkwa]

Re: HP dc7800

Hi, Andy -
Check out post #5 above. The 40W Weller got the job done after I snipped the leads as close to the board as possible. It still meant holding the tip to the board longer than I wanted to, but the Weller worked for both removal and poking the hole clean with a needle. Oh, yeah, I kept swiping the tip off on a wet piece of sponge, which seemed to help a little. At this point I'm kinda figuring if any of these boards don't POST the damage has already been done since resoldering looks pretty straightforward.

I think you're probably on to something as far as a new tip.

Here's the website I found that gave a lot of helpful advice.

I came across several references to solder braid while googling around. I'll try that out on a junk board (not that I'm hoping to create any junk boards in the near future) and see how that works.

[momaka]

Re: HP dc7800

You don't really need a new tip. I've done plenty of motherboard caps with my cheap 35W Radio Shack iron. It's not easy, but it's doable. The best way to do it is to let the iron heat and put a lot of solder on the tip (i.e. make a big blob). Then put flux (both liquid or paste flux will do - just make sure it's the "no clean" type) on the joints of the capacitor you're about to remove. Next, heat with the iron and it should melt the solder much easier regardless if the motherboard uses lead-free or leaded solder. The nice thing about flux is that you don't need to constantly add new solder to the tip or joints in order to have good heat transfer. As long as there is some solder on either one, you will be able to melt it with the iron. Flux is also very useful (actually even necessary) if you do any type of SMD soldering.

OK, thanks, the Good Caps thread mentioned several Matsushita caps (FE & FZ I think?), but FL was only mentioned once so I assumed it was rare.

Probably FC, FM and FR. I don't think there is FE or FZ series from Panasonic. There is FZ series from Sacon - those are extremely horrible (i.e. they usually go bad and litteraly pop/explode). If you have some older mid-to-low end EVGA video cards (and also XFX, I think), check them. They are notorious for having Sacon FZ.

[Telkwa]

Re: HP dc7800

I'll check to see if any of our local stores have "no clean" flux.

I didn't want to put more solder on the board because I was concerned about it going someplace it wasn't supposed to be. And of course I was trying to remove solder, so adding more just didn't seem right. But you're not the first person to mention adding solder to remove the cap so there must be something to that.

[Telkwa]

Re: HP dc7800

Well, I'm done with all 5 PC's that had bulging caps. All of them started and seemed to run OK. I left each one on while I worked on the next one. On some of them I did light tasks like retesting the "Windows Experience" index. They were all set to IDE emulation, so this morning I took one of them and changed the emulation to AHCI, then reinstalled Windows from HP recovery discs. No glitchy behavior at all.

One mb got 4 new caps, two got only one, and two got two. Thanks to everyone for your input, and to Badcaps for the new capacitors.