Re: D9090 repair help

From: Ruud Baltissen (
Date: 2001-08-24 09:49:33

Hallo Ian and others,

I have no experience with a C= harddisk at all but enough experiences in
repairing 6502 based systems. The first question is: is there a schematic
available at all???
If there isn't, then one thing that you, Ian, can do is making one by
re-engeneering the boards you have. Drawing one by hand is enough as I'm
willing to convert it using a schematic-program.

Without a SCH you still can do a lot. At you find a debugger (SCH is
missing for the moment). The core of the design is a flipflop that enables
you to step the processor. This little gadget alone enables you to see if
the 6502 does a proper reset. If it does the addressbus must show $FFFC plus
a byte on the addressbus. You need a multimeter to read the individual bits
from the databus. Step the 6502 and read the next byte.
The two read bytes nust give a valid address. If you read $FFFF for example,
the ROM never has been accessed and you know that something is wrong with
the addressdecoder.

About the cut wires: find out what they connected. This info alone could
give you a clue. If it is a clocksignal, address- or dataline, you can
suspect sabotage. In other cases you simply need the SCH.

  / __|__
 / /  |_/     Groetjes, Ruud
 \ \__|_\

       Message was sent through the cbm-hackers mailing list

Archive generated by hypermail 2.1.1.