[Coco] Zap 0.0.4 Beta has been uploaded to my drop box

[K. Pruitt]

----- Original Message ----- 
From: "Gene Heskett"
To: <coco at maltedmedia.com>
Sent: Tuesday, March 31, 2015 8:12 PM
Subject: Re: [Coco] Zap 0.0.4 Beta has been uploaded to my drop box


<snip>

> The buffers used to translate the 6551's ttl signals up to the +-12 volt
> levels to drive the port to rs-232 specs,  have been rather a nuisance
> to maintain, anyplace they are used, not just with the rs-232 packs, in
> fact I've had less troubles with them there than in most of the other
> places I have found in my life as a broadcast engineer/CET.  Those are
> the mc1488 and mc1489 chips in the rs-232 pack.  The firecracker I
> believe, actually gets its power from the logic levels its being fed
> with and has to make very frugal of that limited power resource.
>
> One of the two is the receiver buffer, converting the incoming line
> signals back to ttl levels for the 6551, and that should not be
> critical, but the transmit buffer is the one I'd replace on general
> principles, it may have lost part of its output stage from an EMP
> (nearby lightning strike, atom bomb...) and can no longer deliver full
> power in one or both directions from ground.  At this late date I do not
> recall which of the two is which, but in the absense of a calibrated
> oscilloscope to confirm its output levels, I would clip the chip out,
> clean up the pin  holes, put in a socket and a fresh chip.
>
> Our rs-232 pack also has another achilles heel, that little tin cased
> Aztec 5 volt to +-12 volt invertor supply.  Mine went away nearly 20
> years back so my pack has been patched to get its +-12 volt power from
> the MPI.  Those 2 voltages should also be checked while its powered up
> and if either of those voltages is under 10 volts, you will probably
> find the tin case is way too hot.  There are electrolytic capacitors
> sealed into it, and if they are failed or in the process (heat is rifle
> bullet deadly to them), it will get hot.  Best bet, which will stop the
> potential for the smoke escapeing is to just unsolder it & remove it,
> bin it, then add some wire wrapping wire to connect from the pins at the
> packs card edge connector to get the +-12 volts it needs from the MPI,
> which can supply it without a struggle.  A cheap digital meter, hot 40
> watt or so soldering iron, wet sponge for wiping iron tip clean, a
> solder sucker, and a small roll of ROSIN cored solder should get you
> going.  And of course a schematic of the rs-232 pack, which ought to be
> available several places on the web.
>
> Good luck & report back with results please.
>
> Cheers, Gene Heskett
> -- 
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>

Wow, thanks Gene.  That was very informative.  And yeah, the CM17A just uses 
logic levels.  I can check the various voltages as suggested which should at 
least tell me if my RS232 pak is working properly or not.  Soldering in my 
MPI or even the RS232 pak honestly just frightens me.  But this definitely 
brings me back to thinking about turning a DC Modem Pak in to a RS232 port 
per Marty Goodman's instructions. One of those I would feel comfortable 
destroying, uh, I mean working on.