Identify this Kemet Tantalum capacitor from HP 16534A

[dorkshoei]

Labelled
R+    (series)
476    (47000000 pF;  47uF)
20K    (20V)
817   (date)

It's from C107 on a HP16534A oscilloscope card.   Smoked on my board (though board still passes self-test and reports correct waveforms against my function generator)

http://alasir.com/reference/kemet_tantalum_capacitors claims that R+ is T495 Industrial (Low ESR, Surge Robust) series

Current Kemet T495 no longer has that R+ label.   Kemet said 817 would be consistent with 1998 when they were "maybe" labeling T495 as R+ but they weren't sure.

There are several of these caps on various parts of the board.     I pulled 3 and all had a capacitance of 47uF and an ESR of between 1.8-2.2 ohms.   Measured using Sencore lc103 and Blue anatek.

Problem is that T495 47uF 20V doesn't come in ESR higher than 150milliohm.     Also according to the Sencore manual for a 47uF 20V tantalum the max allowed ESR is 1.69 ohms.

Possible I'm being clueless; bad measurement of ESR; possible identification of series;  possible it doesn't matter for this application.

[fzabkar]

Try the Wayback Machine:

https://web.archive.org/web/20000831010617/http://www.kemet.com/KEMET/web/pubfiles.nsf/Lookup/T495/$file/T495.PDF

[dorkshoei]

Try the Wayback Machine:

https://web.archive.org/web/20000831010617/http://www.kemet.com/KEMET/web/pubfiles.nsf/Lookup/T495/$file/T495.PDF

Case size I need is I believe X.

T495X476(1)020AS   is  47uF 20V and ESR is 150 milliohm.

They are a "low ESR" cap but I'm curious why all the ones I pulled off my board and measured are 1.8ohm to 2.2ohm.

I have a different [undamaged] board which is how I know what C107 is,  maybe I should try measuring those?  Or maybe I'm just not understanding something?

[fzabkar]

Your caps are 24 years old ...

[dorkshoei]

Your caps are 24 years old ...

Indeed.  I realize ESR increases with age but the values I'm seeing indicate all are outside acceptable range.   Maybe I need to replace all the tantalums on the board,  not an uncommon thing to do for boards this age using tantalum.

Also, DigiKey has the 47uF 20V in stock in 65mOhm, 100mOhm, 150mOhm and 150mOhm/100kHz versions.  Not sure what to order for this application. 

[floobydust]

I see Kemet T495 ESR spec is at 100kHz test frequency and you'll get higher readings below that, depending on your capacitance meter. It might explain the factor of 10 difference you are seeing, but age is a consideration.
Otherwise you'd have to trace the component to see what its doing, what IC etc. to see how critical ESR is. I imagine they wanted medium-low ESR to minimize self-heating, if an SMPS is feeding these regulators? Tantalums with high ESR in the ohms range quickly burn up due to high ripple currents heating them. So check the output caps on the power supply are not high value which causes stress to these small tantalums.

[dorkshoei]

I see Kemet T495 ESR spec is at 100kHz test frequency and you'll get higher readings below that, depending on your capacitance meter. It might explain the factor of 10 difference you are seeing, but age is a consideration.

Thanks.   I'll try and look up the specs of the meters. That old year 2000 catalog shows T495X476[MK]020AS as the only option then for 47uF 20v.   Both 150milliohm.    M doesn't come up but K is listed on DigiKey as superseded by T495X476K020ATE150‎.    I added two to my current order,  I'll measure them when they arrive and see how they compare to the old.

Thanks for the help!