Reviving one of these Apple II or II+ boards

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Ameobob's picture
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Reviving one of these Apple II or II+ boards

I've got an Apple II that I'd like to get working again, and an Apple II+ that is in pretty poor condidion that also would be cool to get working again. I don't trust the II+ board as several of the RAM chips had legs that corroded away and one of the 74 series chip sockets had a corroded away contact as well. All pins on both sets of ROMs (One set of Integer and one set of Applesoft) are intact however, yet neither set will boot past assembly in the II. I did have to repopulate the RAM in the II with new chips from (insert online retailer here), and I did swap over one of the 74 series chips from the II+, yet I still got nothing more than a RAM dump on the II.

My questions to the group: Do you think it's worth looking into the II+, or should I focus first on the II? Which chips are and aren't swappable between the two units? Do you think the issues I'm seeing on the II are due to bad ROMs, bad/incompatible RAM, or something else gone awry? Given the symptoms in the attached videos, what should be my next steps? Is there a good service manual I should be referencing, or some specialist tools that would be useful? Edit: Also, what is the minimum required RAM to get the Apple II to boot up, and given that I have three of the 16k selector blocks (and no others) how can I set that up?

II+ Board: 

https://drive.google.com/file/d/1vn5QGGnN0VX46V1UrcNnP3cb3oZ0-ZX9/view?usp=sharing

II Board (still in case):

https://drive.google.com/file/d/1154uBUzWDDMeSCDF_2YbGdIFLpcRUfk6/view?usp=sharing

Apple II with one set of ROMs:

https://youtu.be/Ki1Obmprzg0

Apple II with the other set of ROMs:

https://youtu.be/juFWQoX2t0w

 

I've also recently acquired three Apple III units and will have a go at them before long.

TIA!

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Your Apple II is probably the

Your Apple II is probably the easier one to fix. Personally I wouldn't give up the corroded one though...

The Apple II basically boots, but then crashes to the monitor since the CPU executes an invalid instruction. This could be caused by a bad ROM. It could just as well be a bad RAM, causing the program flow to go wild. It could also be an issue with the address decoding logic, so the RAM/ROM devices are not properly controlled. It's impossible to tell the difference just from the symptom.

The service manual contains a few tips for such boot symptoms. If you want to try your luck by swapping chips, you can follow the list of suggested chips first. Also check the symptoms when running the built-in diagnostics (press both apple keys when switching on):

https://apple2online.com/web_documents/Apple%20II%20Level%20II%20Service%20Manual%201981.pdf

 

Before anything else I would first check the power-supply though. Make sure the supply voltages are stable, even under load. Checking with an oscilloscope to exclude any significant ripple would be wise. You could keep swapping chips forever, when the issue was caused by a weak supply.

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A couple of answers that
A couple of answers that might help you along. I would probably start with the Apple II as that will give you the best chance of getting a working machine without the need to replace sockets etc. Practically all the chips are interchangeable between those 2 boards From memory those that are not are the character ROM.and the two on the right of the CPU labelled 8T28 which were replaced on the later board with a single 8304 Based on your videos it looks like your close, the 1st one you can see the apple ][ as expected and the 2nd is what you would expect with integer ROMS (At the prompt your should be able to hit control v and that will take you the integer basic prompt '>') If you haven't already done so, raise each chip from the socket and press it in again - it can help with poor connections which is common issue. You only need one ROW of ram (in row C) to start the computer - you can just remove the other rows. The 16K block just indicates how the amount of RAM expected IF the row is populated. Cheers!
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