[rescue] Sun 3/50 memory error

[Curtis H. Wilbar Jr.]

Hi all... I'm trying to rescue a Sun 3/50... actually I have two of them
and at this point I think I'll be lucky if I can rescue one out of the two...

One unit had the internal fuse of the power supply spark/crackle when I
applied power... and something smells in the PS, but I don't see a visible
problem... but that PS is definately gone bye bye...

The other unit I could not get a console on with a terminal... in diag
mode it seems to test fine then when prompted for extra testing, when
I type (faster than a key or so per second) I get DVMA errors from the
OBP... I think I have flow control on on the terminal and have not tried
turning that off yet.  Other than this error I think this mainboard may
work OK.

The other mainboard which I really want to fix has a Parity Systems
memory expansion on it with 4 one meg SIMMS, and slots for 4 more.
So, currently it has 8 meg and is capable of 12.... however here is
the fun... diagnostic aborts on a parity test... here is the error:

Parity error at Addr 0x00001000, Data 0x00000001, Status Exp 0x00000040,
Obs 0x000000F0

So, I'm guessing one of two things... either bad MMU or a bad 
MCM6256BP12 RAM chip (which I think is more likely).  Sun does not
seem to provide a memory map to determine which of the (soldered on
dammit!) memory chips is likely the culprit.

Other then getting the pinout of the chips and pulling output lines
low to try to get the same/different errors to locate the chip (tedious)
I'm unsure as to how to go about determining what to replace.

I did pull the 30 pin simms from the Parity Systems expansion board and
the error occured in the same place.

This is the parity test that preceeds the actual memory test, so maybe
it is the MMU or something else in the parity logic.

So, any ideas ?

I suppose I could remove the parity systems board (as it plugs into the
MMU slot and the MMU plugs into this board)... I could try the MMU from
the working? board... 

Suggestions...

-- Curt