16 Jun
2006
16 Jun
'06
1:43 a.m.
On 6/16/06, David Vohs <netsurfer_x1 at fastmailbox.net> wrote:
I have an SX-64 that has (apparently) a serious
problem. On powerup it
shows nothing on the screen (checked the settings and and also hooked up
an external monitor) along with an occasional crackling sound from the
speaker. Keypresses are not registered by the machine.
Anyone got any ideas as to what the problem could be?
If the power supply is working (check for +5V at the corner of a TTL
chip if you can't find it anywhere else, and see if you can see the
glow of the CRT filament), the next thing to check is the PLA. It's
identical with the one in the C-64, so you can borrow one there. If
it's not either of those, you'll have to start chip-level debugging
(unless you happen to have a C-64 diagnostic cartridge and cable
harness, a tool sometimes used by C= dealers for debugging _mostly_
dead machines). If any of the DRAMs feel _really_ hot (too hot to
keep your finger on), that's a symptom of fried RAM, an occasional
cause of inertness.
The ROMs are different from a C=64, but the only changes to the kernel
are to remove the tape routines (no cassette connector), and change
the default color scheme and startup message.
So... power first, then PLA, then start hunting.
-ethan