The problem that I'm having seems to be very similar to another active issue on Applefritter (http://www.applefritter.com/content/apple-ii-bad-memoryrom) so I wasn't sure if I should add mine onto that thread or start a new one.
I've got a Europlus which has been sitting neglected in the loft for about 20 years, but which I've finally decided to rehabilitate.
When I start it, either from floppy or with the disk controller disconnected, it drops into the monitor at address D44E.
From this document (http://www.textfiles.com/apple/ANATOMY/doswarmstart.txt) I can see that this is in the BASIC warmstart routine which starts at D43C. Comparing the listing there to what I have in my ROM I can see that there are a few significant differences, which I've marked with asterisks below:
Should be
D441: *20* *2E* D5 86 B8 *84* B9 46 D8 *20* B1 00
Mine
D441: *A0* *AE* D5 86 B8 *C4* B9 46 D8 *A0* B1 00
This makes a mockery of the code and so it's no surprise that it conks out!
To simplify things, right at the start I removed the language card (and plugged the gap with one of the RAM chips from the card). The RAM test from that other thread ran ok, although I got question marks rather than little square blocks, which seems to match the description but not the screenshots.
I've 'see-sawed' all the chips on the board to reseat them. I also completely removed ROM D0 and the address decoding chips at F16 and H1 and cleaned their pins with a pencil rubber, a trick that I picked up from another forum post.
Chips replaced and...no difference. I then tried swapping the 74LS138 at F12 with another from elsewhere. Ditto.
I also checked to see if any of the chips on the board are getting particularly hot, which they're not.
The thing is, when it first came down from the loft it didn't work but then, when I turned it on a couple of days later, it was as right as ninepence. The day after that it failed again and hasn't worked since. Unfortunately I didn't take note of how it failed that first time, but its failures have been absolutely consistent since then.
Do ROMS go bad in this way? If it's likely to be one of the support chips, where should I be looking? Unfortunately I don't have an oscilloscope.
Thanks in advance,
Rob
Hello Rob,
Based on your description, the RAM test is successful.
There is apparently a flaw in the ROM. You can try the following things :
1- According to this troubleshooting guide, replace the 74LS08 located at H1
2- Swap D0 and D8 ROMs and look at DC41. If the hexa code is the same that you've already posted, there is a big chance the ROM is bad.
3- If you have a Disk II controller and drive, boot by typing 6P at the monitor prompt (assuming the controller is in slot #6). Then insert a disk into the drive and see what happenned (normally, the Apple will boot the disk). As long as the program doesn't use the BASIC, it will run normally. I suggest a game which relies heavily on assembler.
If you have the ability to recreate a disk using ADT pro, try to boot the II+ diagnostic disk which contains the ROM test.
Hi Antony,
Many thanks for the reply. I've spent the last couple of weeks hunting down a Super Serial Card to use with ADT Pro.
I'll try your suggestions and let you know the outcome!
Thanks again,
Rob