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orange tantalum (?) caps in DEC equipment

S

spiceminer

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Mar 8, 2014
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Dear All!

Anybody knows which values (voltage rating / capacity in uF) can be used as a replacement for
these orange blobs that can be found in DEC equipment?

As an example, I have here a RA72 disk drive which needs cap replacement.

1703435715011.png

On the RA72 the caps have the dimensions 4x6.7mm and 2.2x2.6mm-

thanks a lot
Stephan
 
Yes. A big difference is that there are no markings for polarity on the ones pictured. In my experience, those surface mount caps pictured are either good or very obviously bad.

And a shorted tantalum will make itself known as soon as it catches fire and explodes off the board—at least in my relatively experience with an IBM 5150 motherboard...
 
FYI.
They are tantalum.
Once one did the fireworks thing in my VS 4000/60.
In the pic one can see how it is with those polarity thing...
 

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They aren't tantalums. Tantalum caps do not exist in a bipolar variant. No marking for polarity = no tantalum.
 
It's also worth noting that MLCCs and ceramic caps in general do not share the same age-related degradation of electrolytic (including tantalum) capacitors. Unless I could identify a bad MLCC cap via measurement, I'd leave it alone.
 
Wildfire said:
Uhmm - i thought that picture is self explaining... ???
The polarity markings for the different caps are clearly shown in the picture !
Click to expand...
Where?
index.php
 
In the meantime I have desoldered two of the caps. They are 47 and 1 µF respectively.

I assume that at least one of them is dead because the power supply shuts down when the drive is connected. I cannot be sure that the caps are the reason but I own a RA73 with exactly the same issue where swapping the caps solved the issue.
 
Okay, I see the pin now--they're not at all visible in #1. But if the two you desoldered don't show a short, that's unlikely to be the problem with your unit shutting down. You can probably check the remainder with an ohmmeter in situ.
 
There probably aren't any polarity markings on the PCB. The whole shebang is probably assembled by robots with optical inspection - and they don't have any need for such things as polarity indications!

Dave
 
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