3 Oct
2015
3 Oct
'15
1:44 p.m.
Make/model? (Just in case anyone knows it and knows if
it has any
quirks).
Yamaha C1, one of these:
That would worry me. If one bit of the BIOS program
(as opposed to
copyright messages)
is wrong then the machine could well behave very oddly. Having found
that I would want toget a known-good dump of the BIOS into EPROMs.
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.
That's an odd failure too. Most times true bit-rot
turns 0's into 1's.
Now assuming that first character should be 'C' (or 0x43), then in one
case it becomes 'P' (0x50) and in the other it becomes 0x9A. In neither
case is that simply setting bits that should be cleared. So perhaps
not bit-rot but some other failure of the memory device.
Hmm yea I just looked. I pulled a chip and put it in the reader. The first
read looked similar, then it seems to be going downhill. The reader I have
supports the device directly (ATMEL 27C256), and it's a Needham EMP-100.
Just tried setting it to AMD and a few other brands but I don't think that
changes the read speed or power or anything.
OE/ might be something as simple and MemRd/ (Memory
Read). Is it
bringing CS/ (chip select)
low that often?
Yea the CS is staying active. Since it never really POSTS or brings up the
LCD backlight, it never does a floppy seek. I'm guessing the CPU is stuck
in an instruction loop or something, possibly because BIOS is damaged?
A machine of that vintage may or may not
'shadow' the BIOS ROM -- that
is copy it into RAM for faster access. If it does, then it probably
won't access the ROM once the copy is complete (but is
it completing the copy -- and detecting it has gone through all the
locations ?). If it doesn't (which
is actually quite likely) then it will be running a program from ROM to
set up I/O devices and attempt
to read the boot disk. Which means much of the processor activity _will_
be reading the BIOS ROM.
I'll look through the manual to see if it has an option to shadow ROM
BIOS. I remember that options on the later computers!
When you drop into BIOS, is anything actually set?
Can you set the time, and get it to stick?
Never gets this far unfortunately.
I have a Twinhead 386sx/16 I bought new, the only thing I've used it for in the past
20 years
is a serial terminal, and every time I go to boot it, I have to drop into BIOS, and
configure
things, as the BIOS battery is long dead.
Yup, I've seen that. This machine has a rechargable battery set of 3 coin
looking things in a nice pack that is separated from the motherboard and
everything. Great design. It's a strange laptop format computer that has
no battery option.
Are you getting confused between the BIOS (the I/O
drivers and bootstrap
in EPROM) and the
BIOS parameter table (often called the 'BIOS' or 'CMOS' (as it is stored
in battery-backed CMOS RAM) by the PC crowd)? I was under the impression
that the OP's machine didn't produce any display (does it? If so, what?)
and doesn't respond to the keyboard.
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.
Thanks for the replies!
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.
There is a 3rd Eprom in the machine, it's not a bios and it won't be
readable by the bios dump util I found so another potential issue.
--
Ethan O'Toole