VOGONS


First post, by Intel486dx33

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Hello,
I am interested in repairing some of my old computers with bad capacitors.
but I don't know how to interpret the identifiers on the caps and how to select replacements.
I saw this video by Phil
https://www.youtube.com/watch?v=0vY3DgUbtSM

Does anyone know of a good website that helps to identify the cap types and NEW polymer replacements ?

Reply 1 of 6, by wiretap

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Identifying capacitors:
http://www.robotoid.com/appnotes/electronics- … r-markings.html
https://www.elprocus.com/capacitors-types-applications/
https://www.electronics-tutorials.ws/capacitor/cap_3.html
https://www.eevblog.com/forum/beginners ... pictures)/

For a new replacement, match the capacitance and tolerance, then get the voltage as close as possible without going under. It is ok to get a slightly higher voltage capacitor as a replacement. Also, make sure you get something with an equivalent or better temperature rating so it doesn't die of a heat-related failure. Lastly, of course buy a capacitor with the same leg spacing or SMD size. There are also other parameters you'll want to know for each capacitor type you're replacing, read up on the characteristics in the datasheets to match them accordingly on the new replacement.

I usually buy replacements from Mouser, Digikey, or Newark. Every once in a great while I have to buy something 2nd hand since they aren't made anymore, like some Corning glass molded capacitors that were used in a 1970's GE Logarithmic Radiation Monitor. Things like that can get extremely expensive.. I paid about $800 for a set of 3.. 🤣. Luckily it was for work and reimbursable.

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Reply 3 of 6, by wiretap

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I use Kester no-clean flux, low-tin / high lead solder. (90Pb/10Sn)

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Reply 4 of 6, by ATauenis

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Ordinary oldschool pine rosin for soldering should be a good flux for beginner. It does not require cleaning after use and can indicate overheat. But do not put too much rosin in the place of soldering, otherwise the quality of the soldering will be poorly seen and it will be necessary to scrape the rosin out to check the quality.

Solder? A simple 61% tin-lead solder (like Russian POS-61/ПОС-61) is a good choice. It is better to buy solder in reels. Diameter of the solder should be approx. 1mm. The presence of rosin (flux) inside the solder will not be bad, it simplifies the soldering and saves the external rosin.

The soldering-iron should be approx. 40 watt. 25 watt models are too cold for RoHS (lead-free) solders that are used in PC hardware since late-1990s, and 60W soldering-irons are too hot for motherboards. I am using a old soviet 60 W soldering iron to replace capacitors in modern boards, but there it is necessary to solder very quickly and precisely, for a beginner such a soldering iron will be inconvenient. It's more like a thermorektal cryptanalyzer from communism era, not a soldering iron. 40W are very easier to use, but they're working some slower than hot 60 watt models.

edit: fix typo

Last edited by ATauenis on 2018-06-21, 09:21. Edited 1 time in total.

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Reply 5 of 6, by wiretap

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Recommendation: Practice first on hardware that you don't plan on saving and that's already broken. Watch Youtube tutorials, or go for an IPC 7711/7721 class where you can become proficient. That way you don't further damage a board that you plan on saving. 😀

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Reply 6 of 6, by .legaCy

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I think that a dessoldering iron/pump is a nice tool to have and minimize the chances of anything going wrong, like ripping pads or damaging the board, some multi layered boards are quite annoying to dessolder.
Sure you can "multiplex" the tip of the iron between the two legs of the capacitor but idk , i'm not a huge adept of this meod.

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