Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: Cheap (inexpensive) hard drives
Message-ID: <79342@sun.uucp>
Date: 30 Nov 88 01:58:29 GMT
References: <2570@m2-net.UUCP> <6080009@hpcupt1.HP.COM>
Sender: news@sun.uucp
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 78

In article <6080009@hpcupt1.HP.COM> (Paul Gootherts) writes:
>>	$20  2 Cables              (Some handiwork required)
>
>Please elaborate.  I need to get/make a cable to go from the back of an
>ST-225N (50 pin ribbon) to either a 50 pin SCSI connector or a 25 pin
>MAC connector.
>
>What kind of cable do you run from your drive to your controller?  If
>you built it from scratch, how did you find out what the pin connections
>are?
>- Paul Gootherts, Hewlett-Packard Co, hplabs!hpda!pdg

Building a SCSI cable is fairly straight forward, yet it requires some
manual dexterity and a good vice (smoking won't do :-)). The connector
on the back of nearly every SCSI *device* known to man is a 50 pin
parallel connector (2 rows of 25 pins) with a .1" pin spacing. The 
device will have a male plug the cable will require a female socket.
An "insulation displacement" version of this connector will cost about
$6 list at Active electronics or an equivalent. The "external" connector
is specified by the SCSI standard to be a 50 pin "centronics type" 
connector. These are both a bit more expensive and a bit tougher to 
find. The local sales office of AMP sent me one as a sample, you 
may have to go through Hamilton-Avnet or an equivalent electronics
distributor to get one. The single piece price of these varies, I
was quoted $10. Since there is often a minimum purchase from a distributor
you may end up buying more than one. (Arrow has a minimum purchase of 
$25, the salesperson offered to put one, two or three connectors in the
box :-)) This connector will be a female I believe, since I don't have a 
Mac cable handy I'm guessing. The final piece of the mystery is some
50 conductor flat cable. This stuff is usually gray with a red stripe 
along one side of it. It will cost between $.50 and $1.50 a foot 
depending on your supplier, often, from a surplus store,  you can buy a 
"scrap" cable that uses 50 conductor ribbon cable, cut the ends off
and use the resulting length of cable in your new cable. If you use 
this method you should check for "missing" conductors or damage to the 
ribbon cable. 

Now you have your three pieces, two connectors and a section of ribbon
cable. Carefully disassemble the 50 pin parallel connector and insert
the cable between the "back" and the sharp "spines" on the connector.
Note that the connector has an arrow or dot or the number 1 on the side
where the red stripe should go. Let some of the cable pass through so
that you have about 1/2" of cable on one side of the connector and the
rest on the other side. Now place the whole deal into the vice so that
closing the vice will squeeze the cable between the spines and the "back".
MAKE SURE that the cable is perpindicular to the connector and that the 
spines all line up with conductors in the cable. Then, while keeping the
various parts in place, clamp the vice down on the connector. It will 
"give" slightly when the spines displace the insulation, and the back of
the connector will "snap" into a holding position. When there is no 
gap between the connector pieces and the cable give the vice an additional
quarter turn and count to ten. This will insure the connection. Now
remove the whole assembly and you will have something that from the
side looks like this :
			  
			XXX      <- Connector back
------------------------XXX----- <- Excess Ribbon cable
			XXX      <-- Connector front. 
			XXX

Using a pair of sharp scissors or an exacto knife cut off the excess cable,
fold the remaining cable over the back and attach the strain relief.

Do the exact same thing for the other connector on the other end. 

Now you can connect this cable to your disk drive or what ever inside
the case and leave the 50 pin "centronics" type connector outside of
the case. If you need to go from this connector to a 25 pin Mac type
connector then by a Macintosh SCSI cable (off the shelf at about $19.95)
if you need to go from this connector to another 50 pin centronics 
connector you can get a Macintosh SCSI "extension" cable off the shelf
and use it. I don't reccomend you build your own 25 pin -> 50 pin cable. 

Good luck, 

--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.