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Old 22nd Sep 2020, 11:12 pm   #52
Buzby123's Avatar
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
Posts: 383
Default Re: I found it !. A very sorry looking MK14

I just thought I'd keep you updated on my progress with Micky.

First I traced the ribbon cables to the 32 pin plug, then lots of continuity testing to determine what the daughter board is doing.

It looks like the daughter board does the address decoding for :
0000-01FF : SCIOS ROM on main board ( which I'm fairly certain is the 'new' version. )
0200-05FF : 1K of battery-backed RAM on the daughter board.
0600-07FF : SCIOS ROM on daughter board ( probably the original version. )
? ?? ? : Optional RAM on main board.
? ?? ? : 8154 on main board.

The ? are because I think I've found the reason Micky was abandoned all those years ago. One of the signals for these decodes just connects to fresh air.

Don't laugh, this was my first experience with a microprocessor. I remember having the daughter board working completely ( even though the decode logic is nothing to be proud of ), but I must have done some more mods on the main board and didn't realise that a track cut left a wire floating.

Next job is to find where the floating wire should go, then fix some switches to wiggle the address lines and check the decoding.

A few more hours work, and Micky should be running again.


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