GUBBINS@RADC-TOPS20.ARPA (Gern) (06/08/88)
Zenith H/Z-100 Upgrade Series Part 5 06-JUN-88
Gern
All the world's an analog stage, and digital circuits play only bit parts.
Z-100 Old Motherboard Winchester Modifications
Z-100 Motherboards
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There are two different versions of the Z-100 motherboard. The 'old'
motherboard (Part #85-2653-1) was designed for 192K and 5MHz operation.
The 'new' motherboard (Part #85-2806-1) included design improvements, and
support of 768K and 8MHz operation. The part number of the motherboard is
indicated in the center of the component side (under the video board).
The new motherboard incorporates corrections of the parallel port traces
(all old motherboards had this factory performed). The pizzo-electric
beeper/clicker was moved inward slightly to give the keyboard better
clearance. The new motherboard includes circuit improvements to the memory
timing and addressing logic, refresh clock logic, ready logic, swap logic,
256K RAM support, and wait state logic. The complete text to perform all
the modifications and upgrades to the old motherboard to convert it to the
functional equivalent of a new motherboard is documented in the JUL-85
issue of REMark magazine.
Refresh Clock Modification
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[[[ WARNING: The following modifications should only be done by persons
experienced (or courageous) to make changes to printed circuit boards. The
possiblity exists of permanently damaging the system if a mistake is made.
You make these modifications totally at your own risk. ]]]
Use standard solid conductor wire-wrap wire (#30-#32 gauge).
A soldering iron that is no greater than 25 Watts is recommended.
IC pins when referenced from the bottom (Solder side) of the board appear
in reverse order.
This modification reverses the polarity of the refresh clock. It may have
already been done to your computer, since it is necessary for proper
operation of the Winchester controller. If there are jumper wires
connected to pins 8, 9, and 10 of U130, this modification has already been
done, and the next 5 steps should not be performed.
1. Position the main circuit board so that the solder side is up.
2. Cut the trace coming from U168 pin 11. Make the cut right next to the
pad. [ This is a very small trace from the pad to a perpendicular trace. ]
3. Jumper U130 pin 5 to U130 pin 10.
4. Jumper U130 pin 8 to U152 pin 1.
5. Jumper U130 pin 9 to U225 pin 3.
This completes the refresh clock modification. Power up the system and
test.
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Next: Z-100 new motherboard 768K RAM and 8MHz upgrade.
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