Finding bad RAM chip on PDP11 M7551?
Jerome H. Fine
jhfinedp3k at compsys.to
Mon Oct 16 16:32:12 CDT 2006
>Josh Dersch wrote:
> I have a MicroPDP 11/73 I'm trying to get running again; it has a
> single M7551-AP memory board (1MB) which appears to have a stuck bit;
> the startup memory test fails with:
> Expected Data = 125252
> Bad Data = 125253
> Address = 01400010
> Any ideas how to determine which RAM chip needs to be replaced based
> on the failing address?
Jerome Fine replies:
I don't have an installation guide, but I suspect that
it might be possible to reduce the available memory
until you are able to replace the stuck bit.
Based on the bad memory address, I think that the first
256 KBytes of memory are OK. If you set the end address
jumpers at 256 KBytes, then the start-up diagnostic should
ignore the rest of the memory. If you are able to get by
on 256 KBytes of memory for a while, that might solve the
problem for the moment.
If you attempted to send a reply and the original e-mail
address has been discontinued due a high volume of junk
e-mail, then the semi-permanent e-mail address can be
obtained by replacing the four characters preceding the
'at' with the four digits of the current year.
More information about the cctech