A3000 memory issues

[Motormouth]

I cannot get the last 4 megs of my A3000's 16 megs of on board memory to work.  

The first 12 megs of memory work flawlessly.  However, when I put in the last 4 megs (8 chips) I get the infamous yellow screen on boot.

I have been using 60 ns Page Mode Zips.  I have verified that all 8 chips work (both in this a3000 and in another a3000).  I even went as far as testing each memory chip in the first zip socket of the a3000, all the chip test successfully.  

I tried other page mode zips with the same issue.

I checked all the solder joints of the sockets.  They all seem fine.

Any ideas of what to test next?  I have my o-scope ready at a moments notice.
any addressing line, termination, or signal form the ramsey I should check?

[matt3k]

Hi Motor,

Are there any leaking caps on the mb?

[Zac67]

My 3k had two completely missing (!) solder points on the ZIP sockets. They were so clean that it was very hard to see. I used a fingernail to check if they'd move - two did.

If you're good at soldering and it's pretty sure that one of the banks doesn't work I'd resolder all the bank's sockets. Don't forget to check Ramsey's socket as well...

[Motormouth]

My 3k had two completely missing (!) solder points on the ZIP sockets. They were so clean that it was very hard to see. I used a fingernail to check if they'd move - two did.

If you're good at soldering and it's pretty sure that one of the banks doesn't work I'd resolder all the bank's sockets. Don't forget to check Ramsey's socket as well...

I will attempt to resolder, and report back.  The solder pins are relatively large and should be no problem.

[MinTerm]

Hi Motor,

Did the A3000D boot up properly before you started adding RAM? Or did it go to a yellow screen for no apparent reason one day?

I assume the 8 20-pin DIP sockets (U850D-U857D) are empty and that the 8 ZIP sockets at U850-U857 have the 1Mx4 ZIPs? Both these groups are considered Bank 0 and you won't be able to power up properly if they're both populated. Also, it is important that one does not mix ZIP RAM densities.

You also have to populate the following banks in sequence, starting from Bank 0 or it won't work:

Bank 0 (8 ZIPs) U850-U857
Bank 1 (8 ZIPs) U858-U865
Bank 2 (8 ZIPs) U866-U873
Bank 3 (8 ZIPs) U874-U881

This might be of further use to you (A3000D User Manual, quite detailed for a "User" manual):
http://oldcomputers.net/Amiga_3000_manual.pdf

[Motormouth]

I will attempt to resolder, and report back.  The solder pins are relatively large and should be no problem.

Darn

I did resolder the sockets,  and unfortunately the same symptoms.  I did recheck, all the solder joins and they did look ok.

It is possible that the buffer caps, next to the memory sockets are bad.  These are not electrolytic and should not be prone to leaking however, it fits the symptoms.  Has anyone ever seen these go bad?

Hi Motor,

Did the A3000D boot up properly before you started adding RAM? Or did it go to a yellow screen for no apparent reason one day?

I assume the 8 20-pin DIP sockets (U850D-U857D) are empty and that the 8 ZIP sockets at U850-U857 have the 1Mx4 ZIPs? Both these groups are considered Bank 0 and you won't be able to power up properly if they're both populated. Also, it is important that one does not mix ZIP RAM densities.

You also have to populate the following banks in sequence, starting from Bank 0 or it won't work:

Bank 0 (8 ZIPs) U850-U857
Bank 1 (8 ZIPs) U858-U865
Bank 2 (8 ZIPs) U866-U873
Bank 3 (8 ZIPs) U874-U881

This might be of further use to you (A3000D User Manual, quite detailed for a "User" manual):
http://oldcomputers.net/Amiga_3000_manual.pdf

@MinTerm,

Thanks for the reply, this did happen when adding memory,  This particular A3000 was on the shelf for a while and had 8 megs in it.

Your advise about the memory banks is good one, however in this particular case is not the problem.  I know about the screwy zip bank configuration of the A3000, but it still was a great question to ask.




Also as for the memory, it is all 60ns page mode.  No issues here mixing static and page mode, or speeds.

[mechy]

Pull ramsey chip and check for any bent/corroded pins on it as well as in the socket.May be bad contact at work here.

Also check all motherboard jumpers to be correct and physically disturb each jumper so its making good contact.

mech