Hello!
I've had several reactions on the mail about my broken MSX (Thank you all
who reacted). But I haven't had a reaction that explaines all of the
problems. So I will discuss the reaction and my opion on them...
The first thing I heard was a broken VRAM chip. But if one of those is
really broken, I can't understand the problem the computer has. I thought
the screen with the MSX logo is screen 5, but please correct me if it
isn't. To get the problems described, the screen must be stored in two VRAM
chips of which one is broken. That means the first pixel (4 bits) goes to
chip 1, the second to chip 2, the third to chip 1 etc.
Let's suppose one of those is broken, then the screen will show vertical
black lines. And because the screen is showing them, it is easy to think
this is the problem. But now something I don't understand. Why is the
screen crapped in screen 0? If it is stored in a broken VRAM chip it
schould be completely black, if it is stored in a working VRAM chip it
would be ok and if it is stored in two VRAM chips as described before it
would be partially readable, but even that is not true.
At the opening screen part of the VRAM has been filled with zeros, but in
screen 0 it has been filled with crap. So I don't think it to be likely to
have a broken VRAM chip, but I think there is a problem with sending data
towards the VRAM.
The second problem is the basic problem. Tim Brugman wrote the BIOS reads
from VRAM when interpreting a line. And when it reads crap it will not know
how to process it. But in that case an error message would be displayed,
but that doesn't happen. Instead the two crap characters that appear when I
type 'ok' are displayed. So this explanation is also not quite logical...
Furthermore I've received some reactions that the ROM is not causing the
problems. I can agree on this one, because if there is a mistake in the ROM
it would be very likely for the computer to crash. But this doesn't happen.
The computer doesn't write text to the screen on its own and it still
reacts on the keyboard. Even the return-key is interpreted correctly. So
the ROM will still be ok I think.
Everybody that reacted thought the drive was a separate problem. But I
don't think this is. I've quickly tested it on my 8235 and it worked. That
means, not only the led was working, but so was the drive itself. I only
got an error 'Disk offline', but this can be caused by the problem
mentioned by some people: the rubber snare is not strong enough anymore to
get the disk turning on the right speed. But this won't be a big problem.
The real problem is the 8245 that doesn't send (correct) data to the drive.
Because of this I thought of problems with the I/O. But on the other hand I
had no problems with the sound, so not all I/O is wrong.
The last reaction I received was from Corne Beerse who thought of a power
problem. When the power supply has problems with the 12V the diskdrive
won't run. On the other hand when the 5V is ok, the electronic part of the
computer will run. But if this is the problem, why does the 12V problem
influence the 5V part of the computer. I can't really understand, but then
again I'm not an expert with hardware.
I hope this gives some extra information to everybody who reacted. Again I
want to say I'm no expert with hardware so I can be completely wrong. Don't
get mad at me when I am. I understand it is very difficult to say what is
wrong with my computer when you only have a list of complaints and not the
computer itself and therefore it would be better if I would take the
computer with me when I go to the Zandvoort fare and show what the problems
really are. If somebody want to take a look at it, that is...
Again thanks to all of you that gave me a reaction and I will check some
more things out this weekend. I've left the computer at my parents' home
and I won't be there until friday night. When I find out something more I
will send this to the mailinglist and when somebody suddenly understands
whats wrong with my 8245 please let me know.
Greetings,
Jasper.
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