DEC 3000/600 Alphaserver problems

Peter Coghlan cctalk at
Wed Jan 12 18:09:00 CST 2022

On Wed, 12 Jan 2022 at 17:28:33 -0600 Richard Schauer via cctalk wrote:
> On Wed, 12 Jan 2022, Peter Coghlan via cctalk wrote:
>> They do have spikes of solder sticking out from the positive ends
> Yes, those are tantalum caps.  The "hat" as I've always called it marks 
> the positive end, and it should be part of the case, so it won't melt away 
> in solder.  These things are a bit obsolete and aren't particularly 
> common, but not impossible either.  I use a 100uF 0805-size (2mm x 1.25mm) 
> one of these on a weird board we build for a customer at work; getting 
> that much capacitance in a part that small always amazes me!

This stuff dates from around 1994 I think. My 47uF component is about
6 or 7mm x 3 or 4mm.  Maybe a problem with squeezing a lot of capacitance
in could be that it wants to pop out again!

> I hit Ebay to see if I could find something vaguely like what you have. 
> The first listings that looked plausible were 194453105893 and 
> 203613355685.  I'm not saying they're the right size, or voltage, or 
> anything like it, but it'll get you a manufacturer's part number that you 
> can search for and find like ones.  His price seems high too.  You could, 
> of course, sub an ordinary tantalum.

I probably need to peer closely at all of mine and figure out how many I
need.  There are about 50 of these things in each of three machines :-(

>> I managed to desolder one of them from the middle of the picture using
>> two soldering irons.  I am not very good at this surface mount stuff :-(
>> It came out ok though.  I must have got lucky and picked a good one
>> because it measured 47uF on the capacitance range on my multimeter.
> Two irons is a perfectly valid method of removing SMT parts, if you're 
> quick!  Ever heard of a hot tweezer?  It's two little irons, hinged at the 
> top.  I have a variety of tips for mine and prefer it to hot air for most 
> small things.  (Well, for routine work I usually have a chisel tip on my 
> iron, and can get across both ends of something up to 0805-size and sweep 
> it off the board.  1206 and bigger, you have to get creative, or use the 
> hot tweezer.)

The hot tweezer sounds very nice but I think I'll stick with what I have
for now.  These machines have other problems and won't ever do anything
useful unless I get the cache issues sorted out so I don't necessarily
want to invest in new tools for them to end up not getting them repaired.

Many thanks.


> Richard Schauer

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