Subject: Re: !HELP!! ALTAIR BLEW SMOKE!!!

From: Steve Leach <[email-masked]>
Date: Tue May 27 07:25:59 2003

Well, I must say I'm rather amazed at how quickly I got a response.  
Within an hour of my post, two individuals (Steve Thatcher and Scott 
LaBombard) both provided the information on the tantalum cap, and I 
found the parts at DigiKey.  Thanks guys!

I'm so glad to see some hope at getting the Altair back up and running. 
  When it sizzled popped and smoked, it was like an old friend had died.

If you could humor my electronic ignorance, what exactly IS a tantalum 
cap and how does it differ from a normal capacitor?  I was never before 
aware that there could be more to a capacitor than plates (or foil) and 
an electrolyte.  How can a capacitor have a polarity?

Another question, does anyone know where I can find a replacement for 
the two position front panel switches on the Altair which are marked 
"AMERICAN U.S.A ST1-1" These are 2 pos 3 contact switches, and I've not 
been able to find anything exactly the same dimensions.  I am hoping 
that this is some standard switch and I'm just not aware of it :-)

Also, I've come across rumers of Altair manuals online in PDF format.  
Does anyone know where I could find such a thing?

I'm sure I'll have more questions once I get the poor machine put back 
together and start trying to figure out the disk drives and controllers 
:-)  The machine was stored for over seven years in a barn wrapped in 
plastic bags (not my decision! Don't burn me at the stake!) I wonder 
how many more surprises I'm in for?

---

From: Tothwolf <[email-masked]>
Date: Tue May 27 07:27:49 2003

> that this is some standard switch and I'm just not aware of it :-)

What type of switches are they? Toggle? Rotary? Both C&K and Alco both
manufacture a huge variety of switches, one of which is bound to be a very
close, if not an exact replacement. Are the original switches not
repairable?

-Toth

---

From: "William R. Buckley" <[email-masked]>
Date: Tue May 27 07:28:08 2003

Steve Leach said:

> If you could humor my electronic ignorance, what exactly
> is a tantalum cap and how does it differ from a normal
> capacitor?  I was never before aware that there could be
> more to a capacitor than plates (or foil) and an
> electrolyte.  How can a capacitor have a polarity?

Not an electrolyte, an insulator.  It is the inability to
conduct electrons which gives the capacitor its ability to
collect electrons.  Electrolytes, in general, are ionic
compounds.  Consider the electrolytes of sports drinks.  A
good number of salts constitute the valuable components of
sports drinks.  When dissolved in water, these salts become
the electrolytes.  Now, by being ionic, these electrolytes
are well suited to the conduction of electron flow.  This
is most definately not the kind of behavior which you wish
to obtain from a capacitor.

William R. Buckley

---

From: "Erik S. Klein" <[email-masked]>
Date: Tue May 27 07:28:49 2003

I can't remember exactly where I downloaded the PDF Altair Manuals from,
but I am pretty sure they were for the 8800/8800a and not the 8800B.  If
I find the CD I burned them to I'll check to see if I saved the URL and
if there are 8800B manuals there.  If so, I'll be happy to point you to
the site or mail you a copy of the PDFs if the site is gone.

In the meantime, I would suggest checking out either
www.altairmanuals.com or http://njcc.com/~hjohnson/s100.html.  Both
sites will sell you a copy of the 8800B manuals for a reasonable price.

Good luck!

   Erik Klein
   www.vintage-computer.com/vcforum
   (The Vintage Computer Forum)

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
On Behalf Of Steve Leach
Sent: Sunday, May 25, 2003 7:06 PM
To: [email-masked]
Subject: Re: !HELP!! ALTAIR BLEW SMOKE!!!

---

From: Peter Turnbull <[email-masked]>
Date: Tue May 27 07:30:22 2003

> an electrolyte.  How can a capacitor have a polarity?

Almost all electrolytic caps are polarised.

In principle, a tantalum capacitor is just like an aluminium
electrolytic, only using a more exotic metal (tantalum pentoxide has a
dielectric constant about 4-5 times higher than aluminium oxide) and a
solid electrolyte.  The anode is the foil (or bead, if it's sintered
tantalum tantalum), the oxide layer on it is the dialectric, and the
electrolyte is the cathode.

Passing current from cathode to anode will build up the oxide layer,
the other way will break it down.  From a chemist's point of view,
putting electrons into the cathode and taking them out of the anode
makes some of the metallic aluminium (Al) ionise into Al+++, and if
there are oxygen ions (O--) adjacent, it forms alumina (Al203) --
standard RedOx reaction, exactly the same as anodising aluminium for
protection.  You have to maintain the polarity to maintain the oxide
layer; if you reverse it the electrons will break down the oxide layer.
 The aluminium ions would gain electrons, the oxygen ions would lose
them, the alumina becomes aluminium and oxygen, and then you have no
more highly-insulating aluminium oxide dielctric.

Think of the aluminium-alumina junction as a junction diode, with a
very high resistance in one direction and a very low resistance the
other way.

There's a brief description of construction at
http://www.chipcenter.com/eexpert/akruger/akruger006.html

-- 
Pete						Peter Turnbull
						Network Manager
						University of York

---

From: "Erik S. Klein" <[email-masked]>
Date: Tue May 27 07:34:42 2003

> Does anyone know where I could find such a thing?

I should have remembered immediately.  Rich Cini has the manuals online
(including the operators manual for the 8800B) now at:

http://highgate.comm.sfu.ca/~rcini/classiccmp/Altair32links.htm 

Good luck with your machine!

    Erik Klein

---

From: [email-masked] (Tony Duell)
Date: Tue May 27 07:36:54 2003

> an electrolyte.  How can a capacitor have a polarity?

A capactior is actually 2 plates separated by an insulator, called the 
dielectric. In the case of something like a mylar capacitor (or one of 
the other 'plastic' ones), the dielectric is a thin piece of mylar with 
the metal films (for the plates) deposited on the 2 sides. The whole 
thing is then rolled up to get it into a small enough package.

In an electrolytic capacitor (there are 2 common types, aluminium and 
tantalum), the 2 plates are a metal plate and the electrolyte. The 
dielectric is an oxide film on the surface of the plate. This film is 
very thin, which meance you can get a large capacitance in a small 
package _but_ it will also redisolve into the electrolyte, especially if 
the capacitor is wired up backwards. That's why these units are 
polarised. Connect them backwards and the dielectric disolves, the 
capacitor becomes a short circuit. If enough current can then flow, the 
electrolyte might even boil with the consequent explosion of the can!

Electrolytic caps fail in 2 main ways. Firstly the dielectric might 
redisolve in the electrolyte, causing a short. Secondly the electrolyte 
can evapourate ('dry up'), inceeasing the effective series resistance 
(ESR) of the capacitor.

-tony

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From: [email-masked] (Tony Duell)
Date: Tue May 27 07:37:13 2003

> very high resistance in one direction and a very low resistance the

About 80 years ago, there was a thing called an 'electrolytic rectifier' 
which IIRC used this sort of principle. They were used for low voltages 
in battery charagers, etc. I think I have the instructions for making 
them somewhere, but I've never tried it!

-tony

---

From: Peter Turnbull <[email-masked]>
Date: Wed May 28 01:23:08 2003

On May 25, 20:19, William R. Buckley wrote:
> collect electrons.
> [...] Now, by being ionic, these electrolytes

Not from a capacitor as a whole, but if you look inside the "black
box"...  The discussion was about electrolytic capacitors.  Of course
they have an insulator (the oxide on the aluminium foil anode) but they
also have an electrolyte (which is the cathode), and indeed wouldn't
(don't) work without it.  It's the ability of the electrodes to conduct
electrons that give the capacitor its ability to store them.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York

---

From: [email-masked] (Tony Duell)
Date: Wed May 28 01:31:56 2003

> also have an electrolyte (which is the cathode), and indeed wouldn't

I've met 'engineers' (who darn well should know better) who thought the 
electrolyte was the dielectric (insulator) ! I think I've even seen this 
in print somwehre (but I can't remember which useless book or magazine it 
was in).

-tony