Problem with memory expansion?

[mrknight]

Hi,

I bought an Amiga 500 a couple of weeks ago which included a memory expansion in the expansion slot underneath. While running the computer, I got a couple of Guru Meditation errors. Not always, but often enough to become paranoid. I removed the memory expansion and did not get any errors at all. I inserted the memory again and I started getting errors again.

Some of the errors I got:

I got this error when I booted the computer without a floppy in the drive. Not sure, but it might be 'illegal instruction'.
00000004.OOCO1570

And I got this when I was loading a game. The code indicates 'free twice'.
81000009.265F48F1

The memory expansion is of model HE500 and appears to include a clock.

Is this an indication of faulty expansion memory, and if so, how can I do a memory check to verify the integrity of the memory?

Thank you for your help.

[mrknight]

Your clock battery is leaking acid everywhere and destroying the molecular cohesion.

Spot on. The battery did leak and is dead. I thought the clock would be usable anyway since I assumed it would be powered from the bus connector when the computer is on. I had a closer look today and it seems like one of the copper lanes is broken due to the battery acid. So I have to fix that and find a replacement battery. But it seems like a PCB mounted battery is expensive compared to what is cost to buy a new memory expansion...

Does anyone know where I can find the specifications and pin layouts for the expansion port? This would help me with further trouble shooting.

Edit: I also tested once more with the memory installed and tried to load a game from an Amiga Power cover disk that requires 1Mb of RAM. I got the following two Guru Meditation (I rebooted between each message):
00000003.00C08510
00000003.00C084F8

[mrknight]

Thank you for the link, I found a lot of useful information!

And thanks for the heads up regarding the battery. I assumed it was a non-rechargable battery on the board and was going to replace it with a non-rechargable one. That would have been bad! I will head over to the component shop later today and see what I find. Thanks!

[mrknight]

I changed the battery and checked the copper lanes but I still get these errors. The error seems to be in the expansion RAM range (is it correct that it starts at 0xC00000?) so I have decided to take it out for now.

I have bought a new RAM expansion from UK but this one is without a clock. If everything works with this new board, then I'm happy. If not, then I have to investigate the motherboard for the error. We will see in a couple of weeks...

Thank you all for your help!

[mrknight]

I should run a RAM test but I do not know what program to use, or where to get it. Maybe SysInfo will work? If not, what program do you recommend?

Problem is that I haven't figured out a good way to get files from the PC to the Amiga. I have heard that Amiga Explorer can be installed remotely from the PC onto the Amiga using a serial cable. This is something I need to investigate further.

[mrknight]

Sorry for ressurrecting this old thread but I still have problem with this.

I have been unable to run a RAM test since I don't have the Workbench floppies, and as such, I can not transfer files to the Amiga. I have ordered WB 1.3 floppies from overseas but I haven't received them yet and it has been a month now. If I do not receive them this week I will bring this up with the seller.

The problem only occurs when I am using the memory expansion. If I switch it off or not not plug it in I have no problem. I bought another memory expansion and I still got the same problem. This indicate that something else is not right. How likely is it that two memory expansions have the same problem? The second expansion board does not have a clock.

I did some more research and found out that these Guru Meditation Errors I got is in fact CPU exceptions, where the 0x3 is Address Error and 0x4 is Illegal Instruction.
On Address Error: "An address error exception occurs when the processor attempts to access a word or longword
operand or an instruction at an odd address"
On Illegal Instruction: "Illegal instruction is the term used to refer to any of the word bit patterns that do not match
the bit pattern of the first word of a legal M68000 instruction"

This shouldn't happen unless the software is poorly written. My working theory is that due to a faulty address or data bus line, wrong data is being fetched from the expansion RAM, either by reading from the wrong address or by misreading at the correct address. Maybe I should check the wiring inside the computer? The computer is still sealed so I'm a bit reluctant to open it.

Does all the addressing (from the CPU) to the RAM banks go via Agnus? What about the data bus? Unfortunately, since this problem only occurs "sometimes" it won't be a line that can easily be found. If this is the problem that is. I'd hate to find out that Agnus or the CPU is not working properly=/

scuzzb494, thanks for the schematics! This is so much better to look at than that tiny print in the A500 User's Manual. Thanks!