🚀 go-pugleaf

Since I got my brother's Olivetti M21 Personal Computer while
he's enjoying himself in Australia, this terrible "parity error
on system board" message is haunting me in my dreams. Not that
it would be seriously interfering with the overall performance
of that poor thing, but I can hardly tolerate it.
After startup, the computer displays the following messages, (in
80 char mode) which are coming from the diagnostic routines, I
hope:
 
Resident Diagnostics
Rev. 1.43
 
CPU (i8086) Pass
ROM Module  Pass
DMA Timer   Pass
DMA Control Pass
Interrupts  Pass
640 K RAM   Pass
RT Clock    Pass
Optional ROM at C800:0000
Floppy (A:) Not Ready
 
So far, everything is fine. Now the screen clears and in a
different font (40 char) this disgusting message appears:
 
Parity error on system boardMicrosoft MS-Dos Version 3.20...
 
There is no space between the two messages, the error message
comes right before the DOS Version message. The rest is normal,
if not for date / time:
 
As the date and time were lost each time I turned the computer
off, I thougt that it was just a matter of an exhausted backup
battery for the real-time clock. Indeed the Ni-Cd battery was
dead, so I replaced it with a new and previously loaded one.
Now I got another interesting phenomenon: The computer can keep
track of month and day, but it looses the year information each
time it is turned off, meaning that it always likes to be in
1984, which I find another disgusting thing. The time of day is
correct.
I suspected a faulty real-time clock chip and opened the bastard
again, finding a National Semiconductor MM58174AN, being backed
up by the battery.
I invested about $33 to get this chip from the local dealer,
replaced it and cried out in agony as there is still the same
Parity-error-on-system-board message, the month, day and time
correctly held while losing year information.
Is it because my brother has replaced the CPU with a V30 CPU ?
(what is a V30 anyway ?) Is it because he's got a coprocessor
installed (8087), or is it because of his hard-disk controller
(added later). Is it a hardware or a software problem ? (a
program like CheckIt does find no RAM or ROM problems, however
it says, it "cannot read the AT&T / Olivetti Clock"). If I had
an original 8086, I would try downgrading, but first : HAS
ANYBODY GOT ANY SUGGESTIONS FOR STUPID ME ?
 
Thank you for your replies.