Hi Folks......
Welcome to the simplest logical solution to the dilemma of the A1200 tower
keyboard.
This project was first researched in May 1993, due to the requirements of
fitting an A1200 into a tower at the minimal cost to the client/customer.
It was discovered by myself (Jeff Rose) that most models of A500 keyboard
could in fact be utilised in the same way as the A1200 keyboard connects to
the A1200 motherboard.
The connectors are the same width, 31 connections, so if it worked on a
A500, it was expected that the Commodore engineers would use logic and
simply have moved the connectiom to the centre of the A1200 keyboard, thus
connecting to the A1200 motherboard.
After carefully studying the circuit diagrams of both keyboards, with
confidence, I wired up the keyboard as per these attached diagrams and it
worked first go, complete with reset.
This was then tested on and it worked on Rev 1D4 up to Rev 2B A22200
Motherboards. A logical solution was born to solve the A1200 tower
conversion problem. This information was classified up till now by myself.
Making the small circuit sitting over the ram is simple.
Cut a small copper clad circuit board to fit just over the 4 chips, score
out teh five dividing spaces witha small sharp knife. heat up the small
cut out pieces and they will lift off the printed circuit board leaving
five solder rectangular pads on which to connect via soldering, do not
overheat as they too will lift.
Parts Required:
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the small copper clad board, a ferrite bead, (A500 has many)
a 15µF ~ 22µF capacitor and some colored wires per the drawings.
Doing it:
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The most complex part is the lifting of pins 12 & 13 of the keyboard chip.
this will require an amount of skill, not to get it too hot and not to
overheat
the pads on the 12 & 13 chip legs pads.
I would suggest using a very thin rigid knife sliding it under just as the
solder melts, this will do three things,
(1) this will separate the leg from the pad.
(2) it will lift the leg off the pad due to the thickness of the knife.
(3) finally it will assist in cooling the pad and legs after heating.
Follow the pictures (in color) no black & white diagrams to confuse.
Try to stick to the color wiring patterns I have outlined, this will
aid fault finding.
Be sure to check your work before you power it up, a good digital multimeter
is a good start, the range in price from el-cheapo to really expensive.
The el-cheapo as long as it has a continuity piezo buzzer or similar in it is
fine to use.
It is now for everyone to enjoy !
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Comments to me, Jeff Rose, Managing Director CEO, Unitech Electronics
Pty.Ltd. Est. 1978.
email: jeff@unitechelectronics.com web: http://www.unitechelectronics.com
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Cheers, Jeff
Kindest Regards, Jeffrey. G. Rose. JP C.E.O. and President.
Unitech Electronics P.L. 1978-2002 Dare to be different ! Just do it!
Designers and Manufacturers of Hi-Standard Quality Electronic Equipment
jeff@unitechelectronics.com http://www.unitechelectronics.com 195 Pages
Showroom: 9am-5pm. 8B Tummul Place, St Andrews. Sydney. Australia. 2566
Fax : +61 2 9603 8685 Phone : +61 2 9820 3555
"There is one thing stronger than all the armies of the world,
and that is an idea whose time has come...Neways"
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