The magazine of the Melbourne PC User Group Bad Caps Dennis Parsons |
| Dennis Parsons tells how he began saving motherboards by replacing faulty capacitors |
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Recently I had trouble with a
couple of motherboards. My primary system suddenly stopped booting and wouldn't progress beyond the initial
BIOS screen. This occurred immediately after I installed a new SATA hard drive
so naturally I feared I'd somehow done some serious damage. Fortunately this turned out not to be the cause and things returned to nor- mal after disassembly and testing. I'm not 1009 sure of the cause but I think the DVD writer had slid back in the case and was in contact with the top surface of the motherboard, shorting it out. |
What is a capacitor? An electronic component that temporarily stores electrical charge between a pair of plates. They come in a variety of types including electrolytic, which is the type involved here. |
Recently I had trouble with a
couple of motherboards. My primary system suddenly stopped booting and wouldn't progress beyond the initial
BIOS screen. This occurred immediately after I installed a new SATA hard drive
so naturally I feared I'd somehow done some serious damage.
Fortunately this turned out not to be the cause and things returned to nor- mal
after disassembly and testing. I'm not 1009 sure of the cause but I think the
DVD writer had slid back in the case and was in contact with the top surface of
the motherboard, shorting it out.
The second system, mainly used by my wife and our 2 1/2 year old, was suffering
intermittent problems, misbehaving for want of a better word. Individual
programs were crashing occasionally, including the entire graphical interface
(it's a Linux system) and sometimes the whole system would spontaneously
reboot. Initially it was more annoying than anything as it wasn't happening very
often but the crashes started occurring more frequently and if it kept getting
worse it looked like the sys- tem would rapidly become unusable. Firefox was
sometimes crashing after only a few minutes of use and my favourite file manager
could reliably be induced to core dump (crash and produce a file
containing the memory image for the program). Not good!
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Figure 1: Motherboard
showing row of seven bad caps next to |
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I sought suggestions on the Melb PC newsgroups for solving the problem with the
first motherboard when I ran out of things to try prior to disassembly — I
find it helps to discuss such problems when stuck for ideas. If nothing else
being reminded of the basics can highlight something obvious I may have
overlooked. There is a wide range of expertise readily available on our
groups, something which turned out to be very handy later.
One of the suggestions made was "bad caps" or faulty capacitors — a known cause
of failures in mother- boards, computer power supplies and other consumer
electronic equipment such as DVD players and set top boxes. While the stated
symptoms didn't fit what I saw with the first motherboard (and physical examination
revealed nothing) they certainly did fit with the second. Namely intermittent failures, programs crashing and things gradually getting worse.
I opened the box and bingo! Plain to see were a number of capacitors (nine in
all) with bulging tops, a classic sign of "bad caps" and a very fair bet that
they were the cause of the problems.
What to do?
Having identified the probable cause the next question was what to do about it?
I could leave things as they were as the computer was still usable (after a
fashion), but the crashes were beginning to get very annoying and were likely to
get worse, so some- thing really had to be done. The motherboard was around four
years old and while the system was no race- horse (running an AMD XP1800+ with
256M of RAM) it was quite adequate for the relatively undemanding tasks asked
of it. It would be a shame to just junk it and to my mind
terribly wasteful, although the thought of upgrading my own system and passing
on the old parts had a certain appeal.
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If I was lucky I could source a suitable second hand replacement motherboard
from a computer swap meet or a fellow member but that carried the risk of
developing bad caps too. Having it professionally repaired was possible but given the small value of the board or even compared to the cost of a new motherboard, CPU and RAM, it wasn't worth it. There was also the risk that the faulty capacitors had caused physical damage by leaking or that some other component had suffered electrical damage which could cause the repaired motherboard to fail, or to work for only a short time. This left the option of a DIY repair — a somewhat challenging prospect for someone with my meagre soldering skills and minimal experience of soldering circuit boards, let alone a multi-layer one like a motherboard. The one thing in my favour was I had nothing to lose and if I failed at least I could say "I tried". The failed capacitors were all of the same value, 1500µF 6.3V, with a 1009 failure rate. It's worth noting that different value capacitors by the same manufacturer appeared unaffected. The Repair As it turned out replacement capacitors of the same value were a bit hard to source locally — the usual places (RadioParts, Jaycar, Tandy and DSE) didn't carry them. I found one Australian source online and another was mentioned on the newsgroups but the caps were going to cost about $1.20 each plus an unknown amount for postage. All with no guarantee of success. Not a great deal of money but I'd have to wait for them to arrive. Being a hoarder of old computer parts I had a number of rather old motherboards (Pentium I vintage) moulding away, and they just happened to have 6.3V capacitors on them, although only 1000µF I thought I might be able to cannibalise them to use as replacements and consulted the newsgroup electronics experts (anyone who happened to express an opinion) — the consensus was I'd probably get away with using them. 1500µF or a bit higher than the originals (say 2200µF) would have been better but I didn't have those. |
What is a "bad cap"? Quite literally a capacitor that has failed or gone "bad". Apparently some time in the late 90s there was a case of industrial espionage where the formula for an electrolyte used in electrolytic capacitors was stolen. Unfortunately for many consumers of electronic devices the stolen formulation was incomplete and lacked a vital ingredient to prevent corrosion. Hydrogen gas is produced which eventually causes the capacitor to bulge, split or even pop the casing right off, and the capacitor no longer functions correctly. It's also known as "capacitor plague". Note that even capacitors using a correctly formulated electrolyte have a finite life span due to evaporation (amongst other things) — the hotter they are the shorter their life. For normal computer use you'd expect a capacitor to last decades and not the 3 or 4 years seen with bad caps. Interestingly I found information about a class action in the US against the manufacturer of the motherboard in question which meant they would have repaired it or reimbursed up to US$100 for repairs done. A somewhat academic point as I'm not in the US, but interesting none the less. http://en.wikipeclia.org/wiki/Capacitor_ plague http://www.siliconchip.corn.au/cms/A_30328/article.html |
A 1500µF capacitor with a slightly higher voltage rating (say 10V) while not
ideal would also have been acceptable. My plan was that if they proved
inadequate I'd use pairs of them in parallel to give 2000µF. Achieving this
would be fiddly so I hoped it wouldn't be necessary.
A bad cap will usually (but not always) clearly show one or more of these
physical signs:
A couple of months have passed since I replaced the capacitors and so far so
good. The computer is used every day for at least a couple of hours without any
sign of ongoing problem, so my afternoon of amateur electronics wasn't wasted.
I'm happy, not just because it worked but because I learnt a few things and didn't have to throw out
an otherwise perfectly functional motherboard. With luck it will see several
more years service, but I will keep an eye on the other capacitors.
About the Author
Again I consulted the newsgroups for advice and tips on removing the caps from
the motherboards and re-soldering them. I received some very useful help and
confirmation of some of my own thoughts:
For practice I thought I'd remove a few unwanted capacitors from the old
motherboard I was cannibalising. They came out fairly easily once I'd worked out
how to apply the soldering iron to give the best heating, and this gave me a
degree of confidence. The 1000µF caps came out easily but the damaged caps on
the other motherboard proved a bit more difficult and I had to switch from a 25W
to a 40W soldering iron to have enough heat to melt the solder. All in all
though, it wasn't a hard job.
Soldering the cannibalised replacements into the motherboard was a bit more
problematical. I had trouble cleaning the old solder out of the holes in the
motherboard — I did the best I could without much success. The "legs" on the
caps had to be bent out as the caps were narrower than the originals and because
they were used the wires had already been cut short. This made it all rather
fiddly, holding the caps in place while melting the existing solder, pushing
them in and then topping up the solder to ensure a proper electrical connection.
My soldering technique would undoubtedly horrify the accomplished electronics technician but I adhered to the basic rules as best I could. I
tinned the wires (applying solder to the wires before soldering them to the
board), and applied the solder to the job and not to the soldering iron.
I managed to solder all nine replace- ment caps without doing any apparent
damage to either the motherboard or the caps, although I
did re-solder a couple of them as I wasn't happy with the original effort. It
certainly made for a fairly slow job — thankfully I wasn't being charged by the
hour!
The Outcome
The moment of truth had arrived. I reinstalled the RAM, processor and video card
(removed as precaution against damage), plugged in the power leads and power
button and turned it on. There was no flash, no bang, no cloud of smoke nor even
the slightest of sizzling noises and the BIOS checks appeared on the screen.
Joy! I had deliberately not plugged in the hard drive just in case something
horrible happened when I first powered it up post-repair. As all seemed well I
turned off the power, reconnected the drives and prepared for the real test of
running Linux and trying out the various programs that had been crashing
pre-repair.
All the right things happened when I pressed the power button again —
the BIOS check came and went, Linux ran through its startup normally and I could
log in. Midnight Commander, the file manager that I could reliably crash
pre-repair, was behaving normally with not a core dump in sight. I browsed the
Web using Firefox for over an hour without it crashing once,
where previously it had been lucky to survive 5 minutes of active browsing. This
very definitely smelt of success. As a final test I left the system running for
several hours untouched and when I jiggled the mouse the computer responded, as
opposed to being frozen as was quite common previously.
I was reasonably convinced that my repairs had been successful so I put the
computer back together properly instead of having the motherboard sitting on an
old newspaper (which
by the way is insulating and you won't damage the motherboard when you push down
on it when inserting components). Once reassembled the system still worked and
that part is always pleasing to those who fiddle with computer hardware.
What Are the Signs?
What Are the Symptoms?
• brown staining on top caused by electrolyte venting, with possibly a split
top
The following symptoms are indicative of bad caps:
Note: the above are probably best described as sys- tem instabilities and can
occur randomly during normal computer operation and can also be caused by other
problems such as faulty RAM, overheating, poorly writ- ten software or malware.
Frequent occurrence indicates you have a problem but not necessarily bad caps.
I'd like to say a word of thanks to those members on the Melb PC newsgroups who
offered their knowledge and experience and made suggestions — it was very
helpful and encouraging.
Of note is Mick Marquart who has a thing about bad caps and raised the
possibility in the first place. Recently he has managed to revive a digital set
top box by replacing faulty caps, so next time an electronic device starts
behaving erratically grab a screwdriver and have a look inside. You might just
see the tell tale signs of bad caps.
Figure 3: A wonky row of replacement caps with nice flat tops.
Dennis Parsons is an enthusiastic Melb PC newsgroupie who thoroughly recommends
them to any member. He enjoys tinkering with computer hardware and uses Linux
exclusively.
Reprinted from the April 2007 issue of PC Update, the magazine of Melbourne PC User Group, Australia
