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Question about splitting / swapping byte order to replace ROMs in a Classic II
Posted by: stevenrun34 on 2023-08-22 10:04:20
I have a Classic II Rev B I have been working on where I very unfortunately inserted at least one (maybe both) of the ROM chips the wrong way and nuked it. I had not realized the sockets are 42 pin while the chips are 40--- and stupidly put pin 1 in the hole for what I thought was pin 1 not realizing the pin count mismatch until it was too late.

Anyway-- I have a programmer and some 100ns AM27C400 coming-- and I have a 512KB rom image-- but I am stuck on if I need to byte swap this image BEFORE or AFTER de-interleaving it into Hi / Lo.

I am hoping that one of my chips is still good and I can dump it and compare to see which order of operations I need to do.

I am trying to research for this information, but if anyone has experience or knows the correct answer, I would certainly appreciate it.

Thanks very much!
Posted by: stevenrun34 on 2023-08-25 08:20:23
Replying to myself because I seem to have found my answer and I hope this info can help someone else.

As it turns out, my ROMs are ok, I was able to dump them both and compare to the rom file I had downloaded.

I had been taking the classic II rom I downloaded from the Macintosh Repository and deinterleaving it by one byte-- which was incorrect.

If I had the 4-chip ROM, I would first have to deinterleave the 512KB file every 2 bytes, giving me H and L files. Then I would deinterleave those H and L files by one byte resulting in LL, LH, HL, HH files of 128KB each. Then Byte-swap the split files before burning.

For the 2-chip ROM, I had to split by every 2 bytes first, and then byte swap my hi and lo files. When I did this, the resulting files perfectly matched my dumps.

The tool I use for deinterleaving / byte swapping files is called BINman 4.6.8 which I found on jammarcade.net.
To split by every 2 bytes, you choose the 32-bit option under interleave; and to split by every other byte, you choose the 16 bit option. This wasn't really clear to me until I chose the 8-bit option and got an empty file 😉

Anyway-- back to zero, as I have now made my classic II board (which was booting before and after my recap) dim slightly corrupted vertical bars.

I only tried cleaning the board again because I was getting the wailing / bomb dropping sound from the audio.

I did notice some corrosion around the onboard RAM-- so I will likely try popping off the chips, cleaning underneath, and resoldering. Same goes for the audio chip, and EGRET. Will also recap and clean the analog board.

Anyway-- I've really learned a lot browsing these forums, and I'll be around as I try to resurrect not one, but two Classic IIs I found collecting dust at work.
Posted by: imactheknife on 2023-08-25 19:49:00
Replying to myself because I seem to have found my answer and I hope this info can help someone else.

As it turns out, my ROMs are ok, I was able to dump them both and compare to the rom file I had downloaded.

I had been taking the classic II rom I downloaded from the Macintosh Repository and deinterleaving it by one byte-- which was incorrect.

If I had the 4-chip ROM, I would first have to deinterleave the 512KB file every 2 bytes, giving me H and L files. Then I would deinterleave those H and L files by one byte resulting in LL, LH, HL, HH files of 128KB each. Then Byte-swap the split files before burning.

For the 2-chip ROM, I had to split by every 2 bytes first, and then byte swap my hi and lo files. When I did this, the resulting files perfectly matched my dumps.

The tool I use for deinterleaving / byte swapping files is called BINman 4.6.8 which I found on jammarcade.net.
To split by every 2 bytes, you choose the 32-bit option under interleave; and to split by every other byte, you choose the 16 bit option. This wasn't really clear to me until I chose the 8-bit option and got an empty file 😉

Anyway-- back to zero, as I have now made my classic II board (which was booting before and after my recap) dim slightly corrupted vertical bars.

I only tried cleaning the board again because I was getting the wailing / bomb dropping sound from the audio.

I did notice some corrosion around the onboard RAM-- so I will likely try popping off the chips, cleaning underneath, and resoldering. Same goes for the audio chip, and EGRET. Will also recap and clean the analog board.

Anyway-- I've really learned a lot browsing these forums, and I'll be around as I try to resurrect not one, but two Classic IIs I found collecting dust at work.
Definitely remove egret and sound chip. I pulled all memory chips off too. I ended up having to dremal into the egret as some legs literally turned to dust or close too it when removing it
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