[Coco] IDE interfaces

Dave Philipsen dave at davebiz.com
Thu Mar 17 01:01:42 EDT 2016

I'm definitely not a chemist or a metallurgist. All I can say is that I 
can remember the old game cartridges from long ago having that grey film 
on them and how gently rubbing them with a pencil eraser or even just 
using my fingers would remove some of the junk. And it may just be 
anecdotal but I remember a lot of problems with CoCo stuff but nary a 
problem with Apple II stuff.  All the Apple II boards I ever saw or used 
had gold edge connectors.  And if it is a fallacy that the gold 
connectors improve reliability then a whole lot of pretty smart people 
have been duped!  Are most of the companies who manufacture boards that 
plug into PC slots now migrating away from using gold on the edge 
connectors with this 'new' information coming to light?

Another thing:  If you live in certain areas of this country and do not 
have air conditioning you will almost certainly experience condensing 
humidity if you leave a window open in the evening.  Just looking at the 
forecast for my own location, the temperature is supposed to be at or 
near the dew point at least four times in the next week.  This obviously 
doesn't pose much of a problem for people who control their indoor 
climates but...


On 3/16/2016 4:37 PM, Zippster wrote:
> Thanks for that link John.  That was an interesting read.
> I had understood that the possible issue being talked about was galvanic corrosion,
> which might cause a problem when using dissimilar metals as electrical contacts
> in an electrolyte.  In a “dry” situation like we’ talking about (and this is noted in the paper)
> the electrolyte would be humidity in the air condensing on the contacts.
> I’m just not seeing the electrolyte being present unless you’re in a VERY humid environment.
> And in the conclusion portion of the paper, their tests for gold on tin contacts showed no
> evidence of galvanic corrosion (presumably in air).  Their final conclusion being that the
> gold on tin connectors tested showed no corrosion and were acceptable for
> use in consumer electronics.
> If the connectors in the CoCo are indeed gold plated, then gold wold be ideal on the card edge.
> If they aren’t, (or are and you use a tin card-edge) then the lack of an electrolyte would still seem
> to indicate there wouldn’t be a problem except maybe in super-humid environments.
> It would seem to me all this that normal oxidation on the tin surface (as in storage or just sitting there), which
> doesn’t happen with gold (by itself) would probably outweigh any galvanic effects, and even that would take
> quite a while to happen.
> The way I look at it is it’s probably just fine either way (at least until normal oxidation affects the tin),
> but gold plating is a step up, especially long-term.
> Interesting topic.   :)
> - Ed
>> On Mar 16, 2016, at 3:10 PM, John W. Linville <linville at tuxdriver.com> wrote:
>> There are some papers out there on the topic...
>> 	http://www.jsbtech.com/download/Effects%20of%20Galvanic%20Corrosion%20on%20Au-Sn-Plated%20Contacts.pdf
>> I'm not much of a chemist, so I'm not prepared to render a verdict.
>> John
>> P.S.  I also view "always use gold contacts" with skepticism,
>> especially for hobby projects...
>> On Wed, Mar 16, 2016 at 02:40:39PM -0500, Dave Philipsen wrote:
>>> I wholeheartedly agree with you.  It would take a lot of convincing to make
>>> me believe that gold edge connectors are going to wear out the cart port
>>> more quickly.  And almost all manufacturers of electrical connectors offer
>>> gold-plating as a means of making the connection more reliable.  I remember
>>> many years ago running my fingers across the contacts of those cheapo
>>> cartridges and getting a grey-colored stain on my fingers from the
>>> corrosion.  I've worn a gold-alloyed wedding ring for years and never had
>>> any kind of stain on my fingers from it.
>>> My question to the Facebooksters would be: Why did Intel use gold plating on
>>> millions if not billions of their processors that were intended to mate with
>>> sockets?  Perhaps they could do a little research on galvanic corrosion and
>>> the anodic index of tin https://en.wikipedia.org/wiki/Galvanic_corrosion. An
>>> inspection of the edge connectors on three of my CoCo 3s reveals that they
>>> all appear to have some amount of gold on the contacts. At least Tandy got
>>> that part right.
>>> Dave
>>> On 3/16/2016 2:15 PM, Zippster wrote:
>>>> Gold edge connectors are bad, haven’t you heard?
>>>> Just kidding, but there’s been a small discussion on the Facebook group where it’s being claimed
>>>> tin-plated is better and won’t wear out your CoCo’s cart port connector as quickly as gold.  And that
>>>> that is why Tandy didn’t use it most of the time, not because of cost.
>>>> Personally I don’t  buy it, I think gold plated edge connectors are the way to go, even though they
>>>> cost a bit more.  You can certainly argue it’s not necessary, but worse?  lol.
>>>> - Ed
>>>>> On Mar 16, 2016, at 1:47 PM, Dave Philipsen <dave at davebiz.com> wrote:
>>>>> One thing I noticed about the MiniIDE is that there is no gold on the edge connector.  This is a mistake that shouldn't be repeated if someone decides to design a replacement.
>>>>> Dave
>>>>> On 3/15/2016 6:28 PM, RETRO Innovations wrote:
>>>>>> It'd be interesting to see how small one could make the interface. If one used a flash ROM IC and a CPLD, I think one could put an IDE controller with IDE and CF into a 2.2"x2" form factor.  That's be small enough for any use, no?
>>>>>> JIm
>>>>>> On 3/15/2016 12:51 PM, Tormod Volden wrote:
>>>>>>> On Tue, Mar 15, 2016 at 5:29 PM, Bill Pierce wrote:
>>>>>>>> Some of the Brazillian Coco guys used the schematic from the Glenside unit and made a more "modern" solution that was smaller wih less parts (and fit the slot better). Maybe we could talk them into letting go of the schematic and get Ed to whip some up :-)
>>>>>>> Here are some pictures of both the original Glenside board and the
>>>>>>> Brazilian "MiniIDE": http://amxproject.com/?p=2585
>>>>>>> Some people would probably prefer the big original with "integrated
>>>>>>> MPI" and DIP40 chips, but I'd also be interested in the MiniIDE. Or
>>>>>>> even a CPLD-based remake...
>>>>>>> Tormod
>>>>> -- 
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>> -- 
>> John W. Linville		Someday the world will need a hero, and you
>> linville at tuxdriver.com			might be all we have.  Be ready.
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