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!