[time-nuts] FE-5680A - Newbie capacitor question

[Matthias Welwarsky]

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
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