High Reliability Zip and TWGS Cables

by Bill Shuff


The Zip GS and TransWarp GS accelerator cards which greatly improve the 
performance of the IIgs often have a common weak link.  Both of these 
cards have similar cables that go from the card to the 40-pin CPU 
socket.  These cables can fail due to corrosion of the pins on the CPU 
connector or can fail due to damage to one or more of the solderless 
connections at either end of the cable.  Frequently the failure is due 
to the breakage of the wires of the cable at the point where they are 
pinched by the metal ³forks² in the solderless connectors.  The symptoms 
of cable failure are:

 Intermittent crashing or failure to boot

 Odd characters on the screen

 Problems that sometimes go away for a while when the card is moved or 
 when the CPU socket is moved or pressed upon. 

A replacement cable can be made fairly inexpensively, but it is far 
better to make a replacement with highest quality gold-finished 
connectors.  The connectors I use have longer, wider, and more sturdy 
pins than the original cables.  The gold finish on the metal components 
makes for a very long lasting, reliable, connection both within the 
cable itself and at the CPU and card connections. 

To make a cable it is only necessary to buy the components (connectors, 
and 40 conductor ribbon cable), cut the cable to the correct length, and 
then press the connectors onto the ribbon cable.  The components I use 
are ordered from Digi-Key corporation. Their telephone number is
800-344-4539.  The parts are as follows:

 40 Pin Gold DIP Connector         	Part #CDP40G    	$3.82
 40 Pin Gold Socket Connector		Part #CSC40G	$3.08
 40 Conductor 3M Color Ribbon Cable	Part #MC40M-5    $12.22 for 5 feet

The last item is sold in minimum lengths of 5 feet but the same length 
of 10-conductor cable costing far less could be substituted.  Four 
pieces of that cable placed side by side will work quite well in place 
of a single length of 40-wire cable.  The instructions that follow are 
for a slightly longer than standard ZIP cable only; a TransWarp cable 
requires one modification which will be discussed below.  

Cut a length of ribbon cable to 2 1/4² long and place one end into the 
CPU connector with a bit hanging out of the opposite end of the 
connector.  Be sure the cable is centered in the width of the connector. 
Lock the cable in place by pressing the connector halves with finger 
pressure until it latches and captures tha cable.  Using a clamp or 
vise, press the connector onto the cable.  A piece of wood that is 
thicker than the length of the pins and which fits closely between the 
rows of pins,will allow the connector to be pressed without damaging the 
pins.  Better yet, use a piece of wood that has narrow saw cuts that are 
spaced properly and are deep enough to capture and not touch the pins.  
This will allow the clamping pressure to be placed evenly over the 
entire surface of the connector.  Although the pins and holes of the 
connectors are numbered, the positioning of those numbers relative to 
the construction of the cable can be ignored. The connectors are 
symmetric, and flipping them end for end has no effect on the final 
wiring.

Next, place the smaller connector over the cable with the holes facing 
away from the direction the pins on the CPU connector are pointing.  Be 
sure that it too is centered on the cable and is parallel to the CPU 
connector with 28 mm (1 1/8²) of cable between the connectors.  When the 
connector is positioned correctly, crimp it in place.  Trim the excess 
cable close to the connector edges with a razor blade or sharp knife.  

To make a TransWarp GS cable it is necessary to slit one end of the 
cable into adjacent pairs of wires for a length of about 3/4² using a 
razor blade.  Twist each pair with a needle nose pliers or tweezers or 
your fingers so that each pair of wires will be reversed when the pairs 
are slipped into the thinner socket connecter.  Push the wires from side 
to side to set each one under the appropriate connection point and crimp 
the connector over the wires.  This is a tricky operation, a misplaced 
or un-twisted wire will result in a non-functional cable.  A pair of ice 
cream pop sticks cut to half-width and held together at one end with a 
rubber band serves as a handy tool to hold the twisted pairs in position 
as they are slipped into the connector.  

To make a cable that will allow the accelerator card to go in a slot 
other than #3, add 3/4² to the cable for each slot beyond #3 and add the 
same multiples of 3/4² to the space between connectors as the cable is 
assembled.  

A useful, but non-critical step is to confirm that all connections were 
properly formed using a continuity tester or a multi-meter.  Confirm 
that every pin is connected and confirm that no pin is shorted to 
another pin.  Pins on opposite rows are more likely to be shorted than 
are adjacent pins. If such equipment is unavailable,  it can usually be 
assumed that all went well and prove the correctness of the construction 
by installing the cable and finding that the GS boots and runs properly.