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This problem has gotten progressively worse. It happens with and without the keyboard attached. I've tried reseating chips but nothing seems to have made a difference.
Basically it types a paragraph of random (but uniform) letters then seems to hit return all by itself.
All the time it's doing this, it's beeping an awful lot, like an Apple possessed!
I can interrupt the mayhem intermittently with keypresses, but it continues to repeat the letter e.g. QQQQQQQQQQQQQQWWWWWWWWWWWWWWWWWWWEEEEEEEEEERRRRRRRRRRRR... etc
Are there any ICs I should pay special attention to?
I've searched but couldn't find an example where someone has had this exact problem.
I don't know about the ii+ but if it were any other Apple ii then I would say that one of the contacts on the keys were making contact intermittently. The keyboard needs repair IMHO.
I thought that initially, but this happens even with the keyboard disconnected
Such behaviour is normally related to the strobe and the AKS ( Acknowledge Keystroke )
the related chips are located at the row B and at position B2 ( NE555 ) B3 ( 74LS00 ) and B4 ( 74LS00 )
on mainboard.
all 3 chips together would cost less than 2 Dollars in local electronic shop or electronic shop at ebay
... replace all 3 and the trouble should vanish...
sincerely speedyG
Thank you! I'll purchase those or see if I have some in another working machine and test it out
By the way, the "hitting return by itself" is simply reaching the 256 character limit and starting with a new prompt. Besides that I had no clue till Speedy gave you the lowdown!
Zan
Looks like Speedy has given instructions on how to banish a demon.
Related, the beeping is probably Applesoft telling you you are approaching the 255 character limit.
Thanks for all the help and suggestions guys, I got hold of the correct ICs as recommended by SpeedyG and sure enough, the madness has ceased!