MSI 694d Pro-AR recap

[bushytails]

Board history:
Bought off ebay for $30, free shipping. Seller claimed worked great. Arrives, and of course half the caps have domed tops, only POSTs about half the time with one cpu, and won't even init video with two cpus.

Caps:
6 Tayeh 2700 @ 6.3v. All buldging. Replaced with nichicon 2200 @ 6.3v PM series.
1 Tayeh 1500 @ 6.3v. Looked OK. Replaced with same as above.
4 Teapo 1500 @ 10v. Looked OK, but teapos tend to fail with no physical signs. Replaced with nichicon 1500 @ 10v PM series.
8 Chhsi 1000 @ 6.3v. Half were domed. Replaced with nichicon 1200uf @ 6.3v PL series.
3 Chhsi 470 @ 16v. Looked ok, but were large and had vents, so decided to replace even though they were under 1000uf. Quick check with DMM showed they only had 5v on them. Replaced with same as above.

Total 22 caps replaced.


Replacing:
Replacement was reasonably easy, with only a few of the 8mm ones being a pain to remove. Desoldering station died on the very last lead. Did last lead by pulling the cap out and cleaning with a hot needle. Will need to fix desoldering station before next board...

The four caps near the expansion slots were all installed on their sides, to prevent interference with any cards I might put in. The replacements were quite a bit larger than the originals, and I could easily see them hitting a heat sink or the like...


Why I'm in a bad mood:
After recapping, board posted perfectly with my testing cpu. Went to remove it to put in the real cpus, and noticed one missing smt cap and one damaged one next to the cpu1 socket. Was able to resolder the damaged one, but the other is lost for good. It looks like it's only a power supply bypass cap (in fact, it's in parallel with the new caps I just put in), and the board seems to work fine without it, but it still pisses me off. I checked the pics I took when I first got the board, and they're missing there too... so at least I didn't do it. still pissed off though.


Board-specific notes:
C390 is indeed backwards. Measured it with my DMM, and it has -3.3 volts on it. My other 694d has this cap installed backwards. Installed the new C390 backwards.

The 470uf 16v caps were Chhsi, one of the most failure-prone brands I've seen. They were also pretty large, and had top vents. I decided to replace them as a precaution. A quick DMM check showed they all had 5v on them (and from the board they looked like bypass caps), so just replaced them with the same 1200 @ 6.3 caps I used elsewhere.


Before pics:

The tops of the black Tayeh ones are domed, even though it's not clear in the photo.


Domed tops on the small chhsi caps.


Damaged and missing SMT caps, visible in one of the "before" photos. Also another two slightly buldging tayeh caps and a buldging chssi cap.


After pics:

Overview of the board. Yes, all 22 are visible. Mmmm, shiny!


CPU-area capacitor clusters. Also shiny.


Sideways caps... They'd stick up unacceptably if I put them in normally.


Current results:
Seems to work. POSTs perfectly and reliably with both CPUs in, and voltages appear solid. Haven't done any endurance testing yet though... that will wait until I put it in a box and set it on my desk.


Now I need to fix my desoldering station... have another of these boards to do! Somehow the iron part has clogged internally, so it can't suck... probably will have to clear it with my drill.


--Randy

[willawake]

damn that really sucks, some clumsy bastard was installing the HSF or something. Is that yours or are you buying to recap and sell?

it's only a power supply bypass cap

what is that for?

[bushytails]

Mine... I bought it to replace the p2-350 that's presently the left half of my dual-system setup. I've had plenty of other faster boxes around to replace it (p3-800, duron-750, etc), but decided to wait until I had a good replacement.

(For windows users, you probably don't know that you can do a dual-monitor setup where each monitor is on a separate computer, but things still are shared between them. Upgrading to anything other than windows makes this easy.


Bypass capacitors serve the same function as the large electrolytics, but at much higher frequencies. Electrolytics typically have a much higher impedance at high frequencies, and even the traces on the board have significant inductance when you're talking the frequencies digital logic runs at.

Imagine an inductor between the filter caps (the big ones we all have seen way too many of) and the cpu. This inductor represents both the inductance of the traces and the inductance (non-ESR part of the impedance) of the filter caps. When there's a sudden surge in power draw (say, every clock edge, when CMOS logic draws virtually all of its power), the inductor won't allow the current to change quickly enough, and the voltage would drop. To combat this, a small ceramic capacitor (ceramics have much, much lower impedance than electrolytics) placed right next to the cpu (i.e. after the inductor in the example) is used to supply the highly variable load.

If you look at any high-speed logic board (video cards are good examples, look next to the ram chips. On motherboards it may be a lot harder to find them among all the other components.), most every IC will have a ceramic capacitor next to it, to get around the inductance of the traces.


And, when checking my 694d board to see how easy the other bypass caps were to find on it, I noticed a SMT electrolytic is broken off. Blah. I'll tack on a radial tantalum in its place.


--Randy

[willawake]

thanks for the lesson. Since you have displayed your skills, i think it would be great for you to write in the new FAQ section about what are capacitors, what they do on motherboards and especially why low esr caps are necessary.

Some people also ask about low esr / low impedance and if there is a difference. if you can include both noob info and the interesting stuff for techs that would apprecaite an electronics education that would hit the spot. maybe also what technical parameters make a good cap for motherboards. no hurry though.

1.2oC outside and where is the damn snow :evil: :evil: (i love snow)

are you doing that dual system on linux? i am trying to get samba working on centos but i think i am gonna have to start reading from the beginning about linux networking services to see how it all fits together.

hope you have better success on ebay