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

[Gene Heskett]

On Tuesday 31 March 2015 23:36:38 K. Pruitt wrote:
> ----- 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.

Well, its not as if it was magic. One usually figures out which end of 
the soldering iron gets hot from the first touch. ;-)

Soldering unfortunately is not always an easy thing to teach, because its 
welding without all the fireworks.  The trick is the right iron temp to 
bring the solder to a molten state, somewhere between 550F and 800F 
depending on the solder alloy, good solder needs only 600F, where its 
natural tendency to "wet" the joint is obvious, and use just enough 
solder applied between the tip and the joint to cover the joint.  Get 
back out and don't move a thing for 10 seconds or so for it to fully 
solidify.  It should still have a shine.  Too hot, or something moved 
just as it was solidifying and you'll have a "grainy" appearance to the 
joint, reheat and maybe add just a touch of fresh solder in order to get 
the resin restored & let cool again.  Good eyesight is obviously an 
advantage too.

One of the two young men I had at the tv station when I went in in '84, 
wanted to be my assistant, simply never got the hang of soldering, but 
he had other talents, and has now been the video (commercials mainly) 
production manager for about 20 years, turned out he had a knack for 
that. Him, and a cousin who is now our IT Manager are both badly color 
blind, but a couple demos of what a human face looked like on a 
vectorscope & they had that down pat and forever.

Amazingly, what we perceive as a non-white face, is exactly the same 
color angle on the vectorscope.  The difference between a caucasion 
face, and the blackest african face is all in the brightness levels, the 
peak angle of the color does not change.  That is a hard concept to get 
thru sometimes, to the possessor of said dark face.  They want to insist 
they are different somehow.

Your trivia fact for the day. ;-)

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>