mark@shorty.CS.WISC.EDU (Mark Spankus) (09/16/89)
Greets. I have a friend with a problem with his 128's cartridge port not
working, and I was wondering if anyone else has ever encountered this situation.
Symptoms: Apparently cartridge port was working until one day *poof*. The
machine fails to boot whenever a cartridge is installed. All the cartridges
in question are C64 type. The machine will reset, and depending on the
cartridge, will either come up with a black screen, or the familiar blue C64
screen. The connector itself is clean & has been cleaned since the failure with
the usual Kepro Contact Cleaner. All the address and data lines appear to fine,
as well as IO/1 & IO/2. The EXROM and ???? inputs have been traced back to the
MMU (or was that the PLA? -don't have the schematic with me) and are being
asserted correctly. The machine boots CPM okay, so the Z80 seems to work.
C64 mode and 128 mode also work fine. The only other problem is that the
80 col VDC fails to show the leftmost character and shows random garbage in the
rightmost column (using DESTERM). The cartridges in question work fine on other
computers.
So here I sit. I have tried everyting I can think of, short of replacing chips.
I was hoping someone else has had this problem before & could offer a solution.
Thanks in advance!
-Mark
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Mark Spankus University of Wisconsin - Madison
path: ...!{allegra,heurikon,ihnp4,seismo,ucbvax,uwm-evax}!uwvax!mark
arpa: mark@shorty.cs.wisc.edu
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