11 Mar
2001
11 Mar
'01
1:33 a.m.
This was one of the few missing things in my CBM
collection until yesterday.
The system first appeared dead, showing just a blank screen. But then it
worked fine with any of my assorted game cartridges in the cartridge slot.
To test the disk drive, I pulled out a cartridge-based spreadsheet which had
load and save commands and the disk drive worked OK.
The big surprise was when I put in the Simons Basic cartridge and this heavy
old "portable" C64 came up with its normal opening screen "SX-64
Basic" etc
and it loaded and ran a variety of programs from disk without a problem. But
without a cartridge, or with a C64 Super Expander cartridge, just a blank
screen.
Differential diagnosis of a blank screen on a Commodore (I'm a med student :-)
------------------------------------------------------------------------------
If the screen is *black* your first suspects, in order, are the PLA and then
the VIC-II. Also, as always, check the fuse.
I'm guessing that the blank screen you get is a *white* screen and possibly
a cyan border?
If cartridges work, as they do in yours, the problem is clearly one of the
ROMs. Since the disk drive is operational my first guess is the BASIC ROM,
which is fortunate for you because the Kernal ROM is unique to the SX :-)
I don't remember the number on it, though, but the SX Kernal should be
labelled 251104 with possibly a revision number (-04?). DON'T swap that one
out. The BASIC ROM is probably labelled 901226 but that's in the breadbox
systems. You can take that from any regular C64, and it should work fine.
If both ROMs are shot, all is not lost if you have an EPROM burner -- see this
wonderful archive:
http://www.funet.fi/pub/cbm/firmware/computers/c64/index.html
Just my $0.02! (You adjust for AUS$.)
--
----------------------------- personal page: http://www.armory.com/~spectre/ --
Cameron Kaiser, Point Loma Nazarene University * ckaiser(a)stockholm.ptloma.edu
-- Mickey Mouse wears a Spiro Agnew watch. ------------------------------------