Tutorial: replacing bad capacitors

[glytch] sent in a tutorial on replacing dying capacitors on a motherboard, and we honestly can’t think of a better subject for an introductory tutorial. There’s nothing like having your friends think you’re a wizard for bringing broken electronics back from the grave.

For the repair a dead motherboard was [glytch]‘s quarry. After taking a look at the board, he found a few bulging caps that were ready to burst. After ordering a few caps with the same voltage, capacitance, and dimensions (trust us, you want the same size cap), [glytch] took an iron and desoldering braid to the board and replaced a few caps.

Sooner or later, all capacitors are going to go break down. This isn’t always a bad thing – we picked up quite a few “broken LCD monitors” in the years after the capacitor plague and repaired them with a few dollars worth of caps. A lot of the caps in our late 80s computers have been replaced, and these machines are still chugging along.

Comments

  1. mandoholic says:

    “After ordering a few caps with the same voltage, capacitance, and dimensions…” – In addition, make sure it’s rated for the same or higher temperature or you’re likely to be doing the job again sooner rather than later.

    pd

  2. Ren says:

    A website/forum on replacing bad capacitors,

    badcaps.net

    It helped me in the past.

    (Forumoderator: I’m not trying to SPAM!
    I just think its worth pursuing.)

  3. Hunter says:

    I’ve found it difficult to replace caps on many motherboard because it appears my soldering iron wouldn’t get hot enough to even begin to liquify the solder. Anyone else have this problem?

    • Marshkillz says:

      I have run into this issue quite often when trying to de-solder any capacitors with a lead on a ground plate. the best ways that I have figured to de-solder these is to use a heat gun to either warm that section of the board so that the soldering iron has less to heat up. or to use the heat gun to de-solder it entirely, the latter is riskier as you can start carbonizing the resin in the board.

    • ScottInNH says:

      If you’re trying to do this with a soldering iron and braid or a platic pump… stop right there. :)

      Get yourself a heated desoldering pump. I got one on Amazon for $25 and it’s been a lifesaver.

    • fartface says:

      use a good soldering iron. If it does not say weller on the heat controller stand, it’s not a good soldering iron.

      If you are trying to use a radio shack pencil, stop and save your money for a REAL soldering station. It’s the best $150 you will ever spend.

      • Chris says:

        There are a number of non-Weller manufacturers that are also excellent. Hakko, for instance, is a well respected Japanese manufacturer, and they have a relatively inexpensive temperature controlled station (FX-888) that is perfect for most hobbiest. Many of the chinese knock-offs model their products on Hakko devices.

        I’ve also seen a number of suggestions that the low-end Wellers have dropped in quality since moving to Chinese manufacture.

      • Josh Malone says:

        Let’s not forget Hakko. I love my Hakko 936. You should be able to pick one up for <$100US.

      • dave says:

        No way. If you can’t get the solder hot enough then you need a bigger iron. I can solder anything you can throw at me with a cheapo radio shack iron. Although good equipment makes the job easier, practice is what makes soldering a breeze.

      • Steve-O-Rama says:

        LoL, Weller….

    • Brad says:

      Aside from getting a better iron there is one trick that often works. The reason you are having this issue
      is because the solder they used is a higher lead content and thus the melting point is higher. Your iron almost
      definitely gets hot enough but it is having trouble transfering that heat to the solder you want to melt. To
      help it out melt some new solder ontop of the joint and keep the iron in that blob, much like how water is better at
      transfering heat than air you will find that solder does an amazing job of it. The heat will transfer through
      your cheaper solder into the higher quality stuff and it will melt after a few seconds and then you can remove
      it with your pump.

    • ka1axy says:

      What these guys said. You need a good, temp controlled solder station. Weller is probably the best known name. Get a selection of tips, including one big honkin spade tip for working on ground planes. You will laugh at the puny RadioShack irons.

    • aztraph says:

      Heat gun, i’m with marshkillz on this, but be careful not to bump the board, you may loosen something else and make a mess of the whole project

    • aztraph says:

      It’s seems like that’s all i ever do with computers lately, but i have a question for someone to answer: what kind of tolerance range can be expected out of a capacitor? i’ve looked up charts and see as much as a 30% tolerance, and on the 100 uf i was working with it read 70 uf when i tested it, doesn’t seem right to me. I welcome input

    • Tony says:

      A 4mm chisel tip has been one of my best soldering related purchases. Remarkable heat transfer compared to a pointy conical tip. I find I’m using it for just about everything from soldering big through-hole components to fine-pitch SMD parts.

      • karen green says:

        hello my tv has a bad capacitors which would be better rebuild circuit board or replace the bad capacitors and how much would that cost me its for a 60 inch flat screen. u can contact me by texting @ 862-279-4353… thank you

    • Rachie says:

      I replaced my motherboard cap just last week, and had the same problem. I’m using a Hakko FX-888, so the iron isn’t the problem. I could get the caps out, but I would be left with a plug of solder which simply wouldn’t melt. I tried mixing lower melting leaded solder in, to no effect.

      My solution? Drilling. People already think you’re crazy for taking a soldering iron to a motherboard, so have fun when you tell them you also used a drill.

      • Jim says:

        Watch out with a drill. Many of these holes are lined with a tiny metal sleeve to ensure connection and conductivity between the many layers that make up modern motherboard pcbs, and you don’t want to drill that out.

      • Yann says:

        I did it last week too (looks like there’s a trend or something) and I had the same problem as everybody. Not wanting to invest in a $150 (or 150€ in my case) soldering statino to repair a 30€ motherboard, I tried the small blowtorch for crème brulée I had in the kitchen. Worked liked a charm! I finished the holes with a drill too.

  4. Old Thrashbarg says:

    That tutorial leaves out the most important part: what kind of capacitors to use.

    You can’t just go pick up whatever random caps match the existing values and expect them to work properly, especially not on a modern motherboard. ESR is critical in such applications, so you need to make sure you match (or improve upon) the ESR specs of the original capacitors. In fact, the ESR is often more important than the capacitance value…

  5. Keith says:

    I find that usually a cap goes puffy in two situations:

    – When it has been subject to reverse bias, and therefore there is usually a diode upstream of the cap that needs to be replaced

    – Environment is way too hot – you need to add a fan

    Check the original cause, too. :-)

  6. fartface says:

    “Sooner or later, all capacitors are going to go break down.”

    Not quality ones. And certainly not poly caps.

    I have several rack samplers and synths from the 80’s and early 90’s that all the caps are still perfect.

    Unlike the utter garbage sold today. Yes even a $5000.00 stereo is utter crap quality compared to a regular item from back when they made things to last.

    It says a lot about corporation honesty.

    • Nuno says:

      Hi agree, I also have lots of old caps (10, 20 years old) that still work fine in audio equipment. It’s sad that (some) things are not built to last anymore.

    • Steve-O-Rama says:

      It has more to do with the type of capacitor than the age in which a particular device was built. Your old polyester caps will last forever because there’s nothing to rot or break down. But they don’t offer the same desirable characteristics offered by aluminum electrolytics, e.g. bulk capacitance, and better ripple characteristics. Aluminum electrolytics will last a very long time, as long as the electrolyte is high quality, the seals stay intact, the ripple current doesn’t cause excessive heating, and so on. It depends more upon the designer’s decisions than the capacitors’ characteristics, but there have been exceptions, as noted in previous posts.

      The modern capacitor technology is great. It’s just too bad a group of corporate-influenced EE monkeys had to make it seem so bad.

  7. slinky says:

    I second both the badcaps.net recommendation and the heatgun pre-heat. Most caps are on big power or ground planes, so I preheat to about 220F (using IR thermometer to check) before desoldering or soldering. If I’m quick, I can do two or three leads before having to reheat, but if I get a sticky one, I have to reheat before the next one.

    Be really careful on cheap boards, as the solder pads will lift easily.

    I find pulling one lead partially out, then pulling the other lead all the way out, and finishing with the first lead seems to work best for me in terms of getting the caps out.

    • space says:

      Preheating is PCB saver. It makes everything easier, for example, it is possible to desolder 4700uF/16V capacitor using 25W soldering iron with flat tip. Never had motherboard malfunction after replacing capacitors.

  8. kuhltwo says:

    I have been replacing caps for years. One of the biggest issues was the manufacturer using marginal values. Like 15V caps on a 12v circuit. Also I’ve found, when you replace one, might as well do them all.
    I use a 25w temp controlled iron and a solder sucker. Hot and fast. Even on cheap boards I don’t lift pads.
    I agree that most companies are using the cheapest parts they can get, that’s one of the reasons I use older radio gear for my HAM operations.

  9. robomonkey says:

    Disagree about replacing with the “Same Size Cap” idea. I’ve fixed tons of monitors and motherboards, and in all cases I’ve cranked it up to 11. I keep within a margin of error on Capacitance, but I go high with the voltage and temperature. Even if it means doing some freestyling to get the case to close again, it’s been worth it. Years later, the products still run as if brand new.

  10. Tron9000 says:

    Also: less of a tutorial and more like a report.

    “she was nochalant” -translation- “she said “meh!”

  11. David Mackenzie says:

    Remember that when you power it back up first time – protect your eyes!

    Two weeks ago my adsl modem failed due to this Cap problem and the 10 min fix got me working again supporting a customer who was running our equipment subsea at the other side of the globe at the same time. So a bit of basic knowledge can same you important time and money. Just take care and you will probably never have a cap go bang but just make sure if it all goes wrong you are wearing eye protection.

  12. cgimark says:

    Don’t forget the flux. Without flux on the joints you are relying on whatever flux is left in the solder on the board to flow the joint. With through hole parts this can cause you to have to overheat the joint. The worst caps to replace are those used in high voltage areas on quality boards. Very good manufacturers don’t just solder the large caps in place, they use something similar to a rivet that physically clamps onto the lead before it is soldered, you know when you have one of these because the ring around the lead is clearly visible. My advice with these ?

    Drill out the lead hole with a smaller than the hole bit :)

  13. _glytch says:

    The first time my daily routine of reading hackaday gets interrupted happens to be when one of my little projects gets discussed, hah!

    I’m glad to have sparked some comments but I would just follow up by making one point: The need for a quality soldering iron on a job like this is clearly subjective as I pulled off this fix with a £5 eBay iron.

    A year ago I’d have surely needed a better iron and tip but, with practise, you can make do.

  14. Harald says:

    1. The caps should have a higher temperature limt.

    2. I would propose low-ESR caps

  15. Malikaii says:

    If you are using the heat-gun method, you can use aluminum foil to surround the work area and keep the heat off of other components. It’s the same method those PS3 guys use to reflow their CPUs (could be XBox also).

    As a side note, Wikipedia is in Black-Out mode today, to protest SOPA and PIPA in the US, so if you’re looking to learn about the Capacitor Plague, learn how you can fight SOPA and PIPA instead.

  16. kabukicho2001 says:

    In Lima there’s a guy who apparently fixes pc motherboards. But he only checks caps and regulators. One dollar per repair using used caps and has hundreds of clients per day.

  17. jim says:

    Not very useful, but one of my friends bought a pair of new mobos some years ago and stored them. When he brought them out I was leery they would work. One couldn’t detect RAM, and the other was unstable and covered in busted caps. I have no idea how ostensibly unused boards could be in such a state, but if they were new it appears the electrolyte can react whether or not it’s powered, never mind at high temp.

    After replacing some busted caps and improving the stability, they went in the recycling bin.

  18. Jeff S. says:

    I just replaced the caps in a late-80s DC power supply. The voltage would measure OK with no load, but the output voltage would drop 50% or more under load.

    With new caps, it works just fine. This is on a high end Lambda PS. Long story short – all caps dry out eventually, and need to be replaced. It’s just a matter of time (in this case, 20+ years).

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