Apple III, only Apple II emulation works

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Apple III, only Apple II emulation works

I need some help with my Apple III. Apple III disks don't start, only a very few work actually.

Strangely the Emulations of Apple II work, The Confidence Program works, and Atomic Defense works, but none of the other disks.

The Machine is futher in working order, with the keyboard diconnected the RAM looks to be OK.

 

The Confidence Program gives a Machine Status:

Memory Map good for 128K, although it's a 256K machine and has 256K installed.

Disk drives all checked and the Interrupt System all checked as well.

So something is not working with the memory...

 

Than on the memory test of the confidence program it does show the 256K and all 7 banks and the extension bar.

It passes the Zpage/Alt Stack Page test

and the RAM test stops with the following message:

RAM: BNK 83, ADR 20XX, EXP 20, GOT 22

I have swapped RAM around on the RAM board and it did change the expected and got message sometimes.

I have gotten EXP DD, GOT FD and EXP and EXP 22, GOT 23

 

So I haven´t been able to identify a bad RAM chip.

So my guess is that some of the logic that drives the RAM is faulty. That´s why it sees only the 128K. (shouldn´t SOS run on those 128K?)

Does anybody have a suggestion to identity the chip that is causing this behaviour.

 

Thanks (and Merry Christamas)

Achim

 

 

 

 

 

 

 

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> EXP 20, GOT 22This looks

> EXP 20, GOT 22

This looks like an error with bit 1...

> I have swapped RAM around on the RAM board and it did change the expected and got message sometimes.

> I have gotten EXP DD, GOT FD

0xdd vs 0xfd is an error with bit 5...

> EXP 22, GOT 23

0x22 vs 0x23 is an error with bit 0.

 

Seems that swapping the RAM chips around actually does move the affected RAM bit (each chip holds just one bit of a byte). So, this suggests it could indeed just be a faulty RAM chip and you could probably narrow down the issue? Or have you tried that but the reported faulty bit is completely random and inconsistent with the RAM chips you have swapped?

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Hello Macfly, thanks for you

Hello Macfly, thanks for you input. 

I will keep on swapping a bit and I did just buy another 5V board on eBay.

Haven´t found any good documentation on how the chips on that 5V board are actually positioned.

I tried to guesstimate which chip is which bit and swapping them out inteligently to identify a pattern, I couldn´t...

That´s why I was think it could be a chip that drives the logic, although you are right that in that case it should be independent of swapping.

I´ll give it another go...

 

Also, some of the chips on the board are getting really hot (hotter than in an Apple II) 

Is that normal?

 

 

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achim_boers@mac.com wrote
achim_boers@mac.com wrote:

Haven´t found any good documentation on how the chips on that 5V board are actually positioned.

Also, some of the chips on the board are getting really hot (hotter than in an Apple II) 

Is that normal?

 

The Apple /// Service Reference Manual contains an image showing how the addresses and banks are mapped to the RAM chips of the 5V board and includes a lengthy description of how to decode the error message to an individual RAM bank/chip. See page 13.20 "TRANSLATING ERROR MESSAGES INTO PHYSICAL RAM LOCATIONS" and following pages.

I haven't compared to an Apple II. But if some RAM chips on the same board are hotter than others, than that's a red flag. 

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Macfly, Tried swapping again,

Macfly, 

Tried swapping again, but know with help of the Reference manual, which actually describes exactly this problem in the chapter you mentioned indeed.

With the bad ram chip now identified and by swapping it around in the same bank, the error message is consistent and predictable.

Now just need to get a new RAM chip....

Thanks for pointing me to that part of the reference manual!!

Merry Christmas,

Achim

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Afterall there were 3 bad

Afterall there were 3 bad chips on the board. That would explain why swapping around in the beginning was inconsitent since I was assumin only one chip would be bad. The chips on the 5V board are 4264 DRAMs, I found the same on an early macintosh motherboard (1983), swapped them out and yes! Fiannly can use the Apple ///.

Thanks again!

Achim

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Nice, another happy Apple ///

Nice, another happy Apple /// then (and a happy owner).

Yes, I really like this Apple /// service reference manual. It's so detailed and well done. You can actually narrow down a lot of issues even without looking at the schematics. Amazing times, when they still made manuals like these...

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