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Damn Upgrades!
- Thread starter oldpcguy
- Start date
Caluser2000
Banned
If the previous owne/sr where happy what exactly is the issue?
cryu
Member
I think he was expecting the original Integer BASIC ROMs. That's an Applesoft ROM prompt.
VERAULT
Veteran Member
Origininal Integer ROMS? They show up but they will cost a ton. There are reproduction integer ROMS, I bought one.. Reactive Micro I think. OR you can do ROMX if you just want the ROMS but arent looking for originality.
The system was non-functional and I was asked to repair it. The 555 timer which controls the reset signal was in backwards holding the processor (and the rest of the system) in perpetual reset and one of the DRAM chips was bad. After correcting those issues the system powered on to the screen shown in the picture. Cryu is correct in that I was expecting the integer ROMs so I was disappointed it has the auto start ROMs. I know certain logic boards which have the memory jumper blocks were actually sold as Plus systems however the serial number on the underside of the system begins with "A2S1" which I believe designates it as an non-Plus system.
The problem I am working on now is the keyboard is not functioning at all. No keys register when pressed. I connected my Apple II Plus keyboard and get random characters. Checking the character ROM part numbers the non-Plus system has part number R0-3-2513 whereas the Plus system has part number 341-0036. I suspect this is the reason for the random characters. Does anyone know if I can substitute the Plus character ROM into the non-Plus logic board and then connect the Plus keyboard and have it work? I'm willing to give it a try but wanted to check to see if anyone knew off hand. This would be for testing purposes to ensure the non-Plus logic board is properly functioning. I hear the non-Pls keyboards can be a PITA to repair.
The problem I am working on now is the keyboard is not functioning at all. No keys register when pressed. I connected my Apple II Plus keyboard and get random characters. Checking the character ROM part numbers the non-Plus system has part number R0-3-2513 whereas the Plus system has part number 341-0036. I suspect this is the reason for the random characters. Does anyone know if I can substitute the Plus character ROM into the non-Plus logic board and then connect the Plus keyboard and have it work? I'm willing to give it a try but wanted to check to see if anyone knew off hand. This would be for testing purposes to ensure the non-Plus logic board is properly functioning. I hear the non-Pls keyboards can be a PITA to repair.
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VERAULT
Veteran Member
As far as I know the original II and II plus use the same character ROM interchangeably.
VERAULT
Veteran Member
You dont mean keyboard ROM correct? The character ROM was interchangeable on my Apple II and II plus when I was repairing my original II.
Wayne Stewart
Experienced Member
The Rev 4 was the last Apple II to use the 2513 ROM. The later 341-0036 was not compatible with the Rev 4 and earlier Apple II motherboards. The 341-0036 is a 2716 compatible ROM
The keyboard cable was installed backwards on the keyboard logic board. Installing it correctly brought some life to it (power light and reset key now work) but every key I press results in a dash appearing on the screen. So something is still not working.
I checked the outputs of the U1 and U4 (NAND gates) and the outputs of each gate agree with the inputs (at least the state they were in at the time, I did not pull the chips and perform a full combination test of inputs to output) and I think they're OK. U3, the 555 timer chip, does not appear to be outputting the 10Hz clock signal so it may be bad (I tested with U5 installed and removed). However, I do not feel this is the problem as it appears to be an isolated circuit providing a clock for the repeat key.
Next step is to swap out U5, the keyboard decoder, with one from my Apple II Plus (assuming the Plus keyboard has one. I figure it's easier than scoping out U5. I am also considering that the -12 volts may have been sent back through the keyboard cable and possibly damaged chips on the logic board. If replacing U5 doesn't address the problem that's where I'll look next.
The good news is it appears the keys themselves are all OK. The print a dash on the screen when pressed so that suggests they're operating properly. But I won't be able to confirm until I've solved the keyboard issue.
EDIT: The Apple II Plus keyboard is different from the Apple II keyboard and does not contain 5740 keyboard encoder so I won't be able to troubleshoot by swapping this part.
I checked the outputs of the U1 and U4 (NAND gates) and the outputs of each gate agree with the inputs (at least the state they were in at the time, I did not pull the chips and perform a full combination test of inputs to output) and I think they're OK. U3, the 555 timer chip, does not appear to be outputting the 10Hz clock signal so it may be bad (I tested with U5 installed and removed). However, I do not feel this is the problem as it appears to be an isolated circuit providing a clock for the repeat key.
Next step is to swap out U5, the keyboard decoder, with one from my Apple II Plus (assuming the Plus keyboard has one. I figure it's easier than scoping out U5. I am also considering that the -12 volts may have been sent back through the keyboard cable and possibly damaged chips on the logic board. If replacing U5 doesn't address the problem that's where I'll look next.
The good news is it appears the keys themselves are all OK. The print a dash on the screen when pressed so that suggests they're operating properly. But I won't be able to confirm until I've solved the keyboard issue.
EDIT: The Apple II Plus keyboard is different from the Apple II keyboard and does not contain 5740 keyboard encoder so I won't be able to troubleshoot by swapping this part.
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Wayne Stewart
Experienced Member
The Keyboard encoder is different but you can swap in a complete keyboard with encoder. That’d tell you if the issue is on the motherboard or not
VERAULT
Veteran Member
I dont think thats accurate. I have seen many of the same keyboards on both the II and II plus. IF you speaking of the original (larger of the two datanetics keyboards) Datanetics keyboard (which is NOT the only keyboard used on the original II) yes its proprietary.
You can see this just by perusing the Apple II registry: https://diskpreservation.com/?pg=apple_registry
Thank you for this information as the first thing I did was swap the entire keyboard assembly for my known working Apple II Plus keyboard. It worked better than the original keyboard but there were still issues. If they're interchangeable then this would suggest a problem on the motherboard. I'll try the reverse of swapping the Apple II keyboard into the Apple II Plus.
EDIT: Currently I am suspecting problems with the motherboard and the keyboard. When I plug the known working Apple II Plus keyboard into the Apple II I get different characters when I press keys. When I plug the Apple II keyboard into the Apple II Plus I get the underscore character (as I observed when it was plugged into the Apple II motherboard). If these two keyboard assemblies are interchangeable then there's definitely a problem with both the Apple II keyboard and motherboard.
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The logic board issue was the result of a bad 74LS257 multiplexor (B7) which just happens to be the one (there are two, B6 is the other one) which would have received the -12 volts from the keyboard connector being improperly connected. It now works with my Apple II Plus keyboard. Next up is to troubleshoot the keyboard. I do have to say the keyboard used in the Apple II is really easy to work on (at least for scoping the signals) as the chips, except for one, are easy to access.
I need to order a new 74LS257 so I'll use one out of the Apple II Plus along with the Apple II Plus keyboard to run a diagnostics program on the logic board.
I need to order a new 74LS257 so I'll use one out of the Apple II Plus along with the Apple II Plus keyboard to run a diagnostics program on the logic board.