Finding bad RAM chip on PDP11 M7551?

[Jerome H. Fine]

 >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?
>
> Thanks,
> Josh

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.

Sincerely yours,

Jerome Fine
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