Amiga 3000 mysterious disappearing RAM trick

[Astral]

So I'm still tinkering with the couple of 3000's that I've got. One has a strange problem. There is 16mb of ZIP RAM installed. On first turn on, using various WB loading methods and so on, 16mb is shown. If I reset once, sometimes there is still 16mb, other times there is 4mb. Every reset after the second reset there is only 4mb. Turn off the machine and back on again, and 16mb is shown in all it's glory. I like magic tricks, but not this kind

Now, I have a theory. The 3000 came with the all the current RAM chips already installed, so you would assume that this setup was ok. But, let's not assume. Looking at the chips there is at least 5 different types of RAM. *EDIT* gees! I've just counted 6 different chips. They are all 80ns it appears.

Just how sensitive to mis-matched chips is the 3000, and is the mix/match chip likely to be the cause of the trouble? I'm thinking this is the problem, but just want to get a few opinions...

[Oldsmobile_Mike]

Not too familiar with how the A3000 manages memory, but I'm thinking that you've probably got a loose chip, or a failing chip somewhere in the bunch, which is causing the entire bank of memory to drop out.

I'd start by throwing every memory diagnostic utility you can find at the thing, and maybe contacting Mechware or another vendor, or looking on one of the 'bays for a matching set of chips.  I'd start by swapping these chips for a different set and see if the problem reoccurs, that would narrow it down to a chip issue or a MB issue.

Another thought - can you try running with 8MB, and then with the other 8MB of chips?  See if at either time it drops to 4MB?  At least by doing it this way you could narrow it down.

Could it be power supply related?  A weak or failing PSU not providing enough juice for all the chips?

Good luck!

[nicholas]

Could be the PSU on it's way out.

Is it a standard A3000 or do you have an accelerator or any Zorro cards attached?

[mechy]

So I'm still tinkering with the couple of 3000's that I've got. One has a strange problem. There is 16mb of ZIP RAM installed. On first turn on, using various WB loading methods and so on, 16mb is shown. If I reset once, sometimes there is still 16mb, other times there is 4mb. Every reset after the second reset there is only 4mb. Turn off the machine and back on again, and 16mb is shown in all it's glory. I like magic tricks, but not this kind

Now, I have a theory. The 3000 came with the all the current RAM chips already installed, so you would assume that this setup was ok. But, let's not assume. Looking at the chips there is at least 5 different types of RAM. *EDIT* gees! I've just counted 6 different chips. They are all 80ns it appears.

Just how sensitive to mis-matched chips is the 3000, and is the mix/match chip likely to be the cause of the trouble? I'm thinking this is the problem, but just want to get a few opinions...

sounds like a zip is not installed right or making good contact. a bent leg that makes intermittent contact with the socket could be causing this.
A zip that is on its way out could also cause this,but i'm guessing a bad connection. Reseat the custom chips(ramsey,dmac,etc) also. bad connection in the socket could act up.

Generally different brands of ram should live together fine..

If you are mixing page mode(part # ends in 400) with static column ram(part # ends in 402) be sure the static column is first in the zip sockets.

[matt3k]

sounds like a zip is not installed right or making good contact. a bent leg that makes intermittent contact with the socket could be causing this.
A zip that is on its way out could also cause this,but i'm guessing a bad connection. Reseat the custom chips(ramsey,dmac,etc) also. bad connection in the socket could act up.

Generally different brands of ram should live together fine..

If you are mixing page mode(part # ends in 400) with static column ram(part # ends in 402) be sure the static column is first in the zip sockets.

Agree it is probably not seated well, but I have seen 3000's give issues when certain brands are mixed.  This is going back almost 20 years and I don't remember the details.  Try using 8 megs at a time and see if it's stable.  Could run an intensive memory test over night to see if something comes up.

I think you would want Page Mode in the first socket and not Static, since you would want the all the zips to run in page mode.