Author Topic: Small value electrolythic capacitors, replace tantalums or not in analog board ?  (Read 966 times)

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Offline DC1MC

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So, while waiting for my logic analyzer to reach me form the showy hills of UK I've decided to start replacing some elcos on my Solartron 7150 DMMs.

There I've found the usual dried blue Phillips elcos (thanks god they didn't leak) and some strange animals that I wanted to ask the forum about:

Some little axial polarized capacitors that proved to be 1uF/35V KEMET tantalums. I've removed one and put it on my LCR and has some mediocre results (large ESR).

So the question is, should I replace them at all or should I live them alone ?

And if I'll replace them, should I get tantalums or should I get up-specked elcos, for example 2.2uF /63V ?

Any advice is appreciated,
DC1MC
 

Offline Bashstreet

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It kind of depends of their usage in the equipment and without schematic it is impossible for me to say.

Any case if you want to restore the equipment to factory stats you should replace them all (if it is feasible and there are not 300 of them)

How many are there ?
 

Online bd139

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Are they orange or silver ones?  The orange ones need replacing. Silver ones (wet tantalum) are probably fine.
 

Offline DC1MC

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There are silver ones, it has an ESR of 1Ohm, is that normal ?
There are 3 or 4 per board  and I have 2 boards to update, my main concern was if I get better with an aluminum 2,2uF at 63V instead of 1uF/35V tantalum as it is.
They are not in the signal path but as decoupling for some analogue stages.
 

Offline Gyro

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Are they orange or silver ones?  The orange ones need replacing. Silver ones (wet tantalum) are probably fine.

They are much more likely to be standard Kemet axial hermetic dry Tantalums (also silver). I've never known them to cause problems, unlike the ordinary beads ones.... https://search.kemet.com/component-edge/#/browsing?search=axial%20tantalum&id=348 Wet tantalums are reserved for very specific purposes.

@DC1MC: They are probably being used as bulk capacitors to back up the ceramic decouplers. At 1uF their measured ESR at whatever frequency your meter uses will probably read high anyway. I wouldn't replace them with ordinary electrolytics.

« Last Edit: January 03, 2018, 07:53:16 pm by Gyro »
Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline DC1MC

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Are they orange or silver ones?  The orange ones need replacing. Silver ones (wet tantalum) are probably fine.

They are much more likely to be standard Kemet axial hermetic dry Tantalums (also silver). I've never known them to cause problems, unlike the ordinary beads ones.... https://search.kemet.com/component-edge/#/browsing?search=axial%20tantalum&id=348 Wet tantalums are reserved for very specific purposes.

@DC1MC: They are probably being used as bulk capacitors to back up the ceramic decouplers. At 1uF their measured ESR at whatever frequency your meter uses will probably read high anyway. I wouldn't replace them with ordinary electrolytics.

OK, the miserable blue Phillips axials were really dried, but those axial tantalum guys were new to me and I didn't know what is their behavior in time, OK, they will stay put and live to filter another day or decade :).

 Thanks for help,
 Mircea
 

Online bd139

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Check to make sure there aren't any RIFA "gold" X2's in the power supply as well if you haven't already! Those blow up and do a lot of damage (and make my wife angry because of the awful smell :-DD )

They seem to almost always be in kit with Philips axial electrolytics in.
 


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