3 Oct
2015
3 Oct
'15
2:05 p.m.
On Sat, 3 Oct 2015, ethan at 757.org wrote:
Yamaha C1, one of these:
It doesn't behave at all. The LCD backlight never comes on, and it always
thinks that it's in external video mode. There is a dip switch on the back to
set this between internal and external display, and it never switches to
internal. I don't have a CGA monitor, but I tried to cross wire a Commodore
1084S over to it and nothing.
Using your oscilloscope, does the external video connector show anythings
resembling a video signal?
BTW, SOME after-market "CGA" connectors added a signal for composite
video, which would be relatively easy to interface to. Does your manual
have connector pinout?
Yea the CS is staying active. Since it never really
POSTS or brings up the
LCD backlight, it never does a floppy seek.
Do you have a floppy in the drive? Some "smart" systems won't try to seek
the floppy if they already figured out that there's no disk in it.
I'm guessing the CPU is stuck in
an instruction loop or something, possibly because BIOS is damaged?
That, unfortunately seems likely. On a 286 machine with internal/external
video, the BIOS is likely to be farily unique, unlike most desktops, where
many other BIOSs would work.
No display, the LCD actually never lights up. There is
an option to switch
between external CGA or internal LCD, no matter what setting the dip switch
is set to it always says external display -- another hint that something is
very wrong.
"SAYS external display"? how? by lighting an LED?
I'm trying to find someone with a working machine
and going to ask them to
run a bios dump utility. Not sure if it will work but short of finding a
working specimin it's my next hope.
If you can find a duplicate machine, that can confirm/solve bad BIOS.
--
Grumpy Ol' Fred cisin at xenosoft.com