Tantalum capacitors are known to occasionally short for no good reason. Give them a reason and they'll be happy to oblige. Things that can damage a tantalum cap in a hurry include excessive voltage, reverse polarity, overheating (likely with hand soldering) and current spikes. If it were me, and assuming it is at the input of a linear regulator, I would put a ceramic multilayer capacitor in its place. It will likely be much smaller (requiring a short jumper to match the solder pads of the larger tantalum) but a lot more reliable, and you are less likely to damage it by hand soldering. (some linear regulators are unstable with a large ceramic capacitor on the output without proper damping, but there is typically no issue at the input)
Didier KO4BB On Sat, May 2, 2020 at 2:59 AM Matthias Welwarsky <[email protected]> wrote: > On Freitag, 1. Mai 2020 23:42:46 CEST John Bievenour wrote: > > I'm an amateur electronics hobbyist who's still a newbie (especially to > > SMD), so please forgive the basic question. > > > > I recently acquired a FE-5680A that was failing to lock on frequency > (pin 3 > > never went low). It will power up, sweep up and down, and finally settle > to > > fluctuate around 9.9999999 to 10.0000000. > > > > When I opened the case, I found that one of the capacitors had blown, > which > > I believe might be the reason. Looking at the top of the board, with the > > DB9 on your left, the capacitor in question directly across from the > right > > hand 2941 voltage regulator. It has 105 on the first row, 35 followed by > a > > stylized K on the second row, and 333 on the last row. > > > > I'd like to attempt to replace the blown cap. After doing lots of > searching > > and reading, I'm pretty sure this is a Kemet 35 VDC 1uF SMD Tantalum > > Capacitor (never knew these existed until yesterday). I've narrowed down > > the options on Mouser, but I can't figure out: > > > > 1) is my identification correct? > > Sounds about right, going by the images I found. > > > 2) is it a T489, T491, T494, T495, T496, T498, or T499 (the band at the > top > > makes me think it's a T498, T491, T494, T495, T498, or a T499) ? 3) is > the > > tolerance 10% or 20% (I think it's 10%)? > > > 4) what is the ESR (I have options from 1 Ohm to 83 mOhms)? > > I don't think you need to worry about that too much. The capacitor is > probably > for filtering on the input of the regulator. For output filtering it's too > small. The datasheet for the LM2941 I found says at least 22µF is needed > for > stable operation and ESR between 100mOhm 1 Ohm. So, the output filter cap > must > be somewhere else. > > Just make sure the size matches. The band on the top only marks the > positive > side of the capacitor. > > > 5) for future reference, how am I able to tell the tolerance, ESR, and > > series just by decoding the writing on it? > > Without knowing the exact part number and looking up the values in the > data > sheet it's impossible to know these details. I usually compare the top > markings against manufacturer data sheets until I find a close match and > then > go from there. > > > > > Thank you very much in advance. > > - John > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and > follow > > the instructions there. > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
