From: neufeld@helios.physics.utoronto.ca (Christopher Neufeld)
Subject: Re: Odd Hardware Question
Organization: University of Toronto Physics/Astronomy/CITA
Date: Wed, 27 Jan 1993 21:29:21 GMT

In article <1993Jan26.152555.25661@aio.jsc.nasa.gov> mark@pokey.jsc.nasa.gov (Mark Manning) writes:
>It is kind of hard to tell exactly what is going on from the diagram.
>However, if this is the kind of cable I am thinking it is (a ribbon
>cable) then taping it is not going to do much good.  The most likely
>reason the system is crashing is because the wires are touching in
>the ribbon cable.  This means that somehow you have to separate the
>wires with some kind of insulation.  And on a ribbon cable this is
>not an easy task.
>
   Because of the way those cables are designed, it's hard to imagine
the individual conductors touching each other. One thing about the end
connector, it makes pretty well no difference if the entire top plate
falls off, the conductors are all in good electrical contact with the
appropriate pins on the plug which fits in the 65816 socket on your ][GS
mother board. If the top plate is coming loose it is probably not the
cause of your intermittent failures. Still, it can't hurt to find out.
Just push the ends back together (see below).

>Actually, I would take the entire thing out, open it carefully (if
>possible) and see if you can replace the ribbon cable.  If this is
>possible, then Radio Shack or any number of other good electrical
>outlet stores could get you a replacement cable.
>
   If it is an intermittent short between the conductors, this is not
necessary. Merely cut off the last two centimetres of the cable (ie. the
part of the cable which is embedded in the plug; don't worry, there's
quite a bit of cable there) and buy a new plug. They cost $10, I know
since I broke one on my Zip. Once you have the new plug, put the cable
through it and stick a thick piece of wood against the bottom half of the
plug, between the pins, so that the wood projects out farther than the
pins. Now you can use a workbench vise to squeeze the connector shut.
This forces the pins knife-edges attached to the pins of the plug to go
through the insulator of the ribbon cable and attach to the wires inside.
I've done this a few times.
   You want to avoid having to replace the ribbon itself because the
other end of it, the end which plugs onto the Zip board, is much narrower
and so is more heavily stressed by the attachment procedure (smaller
contact area, same force required to push through the insulator). You'd
rather not have to attach that connector to a ribbon cable, if at all
possible. There are special vises and attachments to do this, but they're
ridiculously expensive.

   BTW, ribbon cables are very cheap, as are (plastic) end connectors. I
built a SCSI daisy-chaining cable for $14 in parts obtained at a surplus
store. It works very well.

>If, however, you can not find a cable and chip assembly, then you
>will have to get out your solder gun, call the manufacturer, and
>go over how to create the thing.  Again, you will be on your own
>when you create the new cable and there is always the possibility that
>you will do more damage than good - you just have to decide if that
>is what you want to try.
>
   You never solder these cables! That's why knife-clamp connectors were
made, so you didn't have to worry about getting all 24 wires soldered
properly with no shorts. The SCSI cable I made is a 50 pin ribbon and two
50 pin connectors. It took me less than three minutes to make all 100
electrical connections with a vise and some padding (to protect the
connectors from the corrugated metal faces of the vise).


-- 
 Christopher Neufeld....Just a graduate student  | Everyone talks about
 neufeld@helios.physics.utoronto.ca    Ad astra  | apathy, but no one does
 utzoo.utoronto.ca!generic!cneufeld              | anything about it.
 "Don't edit reality for the sake of simplicity" |