amiga 4000 simm slots only addressing 1 meg per slot

[mechy]

this is just a shot in the dark,but i had a similar issue long ago on a 4000 that someone had stuck A1200 roms in for some unknown reason,it will boot with 1200 roms but you will get trouble like you describe. if memory serves the chip ram showed up fine but fast always had a problem.Just something to check.

i would suspect the simms you are using off hand otherwise.Can you try it with 2-8MB simms instead of the 4-4MB simms?

dirty/tarnished simm slots could do this,but i would suspect you would be getting odd size ram reports.

Has the board you are working on been battery damaged in any way?
mech

[mechy]

Thanks for the ideas.  the roms appear to be a4000 3.1  40.68
I tried your idea of the 2-8mb simms.  One in bank 1 (slot 2) and one in bank 3 (slot 4), I get 4mb of fast ram.  If I put in one 8mg simm into bank 1 (or the 2nd slot) I get 2megs of fast ram.  So the problem is unfortunately consistent.

As for the battery damage it is very minor.  I did check the U891 74LS245.  it appears to be working.  It appears to have been cleaned.  Just in case I cleaned it more.  All the simm slots seem to be ok.

There are only a couple of socketed things on the motherboard.  One is the cpu slot.  I put in a A3640 from one of my A3000, to see if that was the problem.  I had the same issue.

The A4000 came with a -09 buster.  I put an -11 in it.  Again same problem.

Arrggg.  
It appears be something annoying minor.  I have to admit this is frustrating.

I am going to hook it up to an Oscilloscope after work tomorrow.  If I only knew which look for.  I found the A4000 Rev B schematics on line.  I wonder if the problem is somehow the ramsey?  or a single simm slot line?

Its sounding more and more like a broken/bad trace somewhere. can u ohm them out from ram slots to chips and see? or u mentioned a scope,may be the ticket there.

please let us know what you find!

mech