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Compatible eeprom for Classic II ROM replacement
Posted by: Alexandre on 2020-11-22 06:47:24
Hi everyone

I wish to know if it possible to use some eeproms to replace my Macintosh Classic II 2 x ROM chip.

I connected one of thoses in a bad position and not the macintosh just do not see any scsi device... and i get stuck on the disk icon with a ? mark who make me think that my rom are now defective...

I have some 27C400 rom and a eeprom burner so i wonder if there a possibility to download the rom from internet then burn it back to a pinout compatible eeprom? and which type of eeprom would be compatible?

Thank you very much for your help
Posted by: dochilli on 2020-11-22 07:32:09
ROM download:

https://www.macintoshrepository.org/7038-all-macintosh-roms-68k-ppc-

Sometimes must be splitted up into 2 Files.
Posted by: Alexandre on 2020-11-22 07:35:13
Thank you. Yes i already have the 512k rom file now i need to know how it possible to split it in two file? and also there is it a eeprom pinout compatible for Macintosh Classic IIK rom?
Posted by: Bolle on 2020-11-22 08:32:40
When you make it to the flashing question mark your ROM is fine. It would have failed the checksum test if it wasn’t.

To verify you can read it with your programer and compare it to the ROM file you got from the internet.
Posted by: dochilli on 2020-11-22 08:33:11
Software:
Posted by: Alexandre on 2020-11-22 08:40:56
Thank you! I will have a look to your software... Also im wondering can i burn the 512k image to 1 x 27c400 for examble...then use only 1 chip on the board if i set the jumper to 512k?

And does someone know if 27c400 will be pine-out compatible?

Thank again 🙂
Posted by: 360alaska on 2020-11-23 09:10:40
This may be of some help: http://www.synack.net/~bbraun/classic2.html
Posted by: Alexandre on 2020-11-23 16:12:37
This may be of some help: http://www.synack.net/~bbraun/classic2.html
Thank you very much! I looked at this blog earlier but im not sure to understand if his modified rom could be used alone without Classic II FPU/ROM Card?

My main concern is about to know that if i split a mac classic II rom to get 2 x 256k rom file then i burn thoses files on 2 x 27c400 should it work as it? I just cant find any information on internet that can confirm this... so i wonder if someone already did this?

Thank for your help and sorry for my not so good english
Posted by: 360alaska on 2020-11-23 20:32:31
You should be able to use it without the rom card, just don't use the modified system rom. You can always email @bbraun.
Posted by: karrots on 2020-11-23 20:49:16
He specifically says you can:

The 2 ROM version of Classic II can use two 27c400 EPROMs of 100ns or faster (150ns won't work) to replace the system ROMs. The 4 ROM version can use four 27c010's. I did my development with the 2 ROM version because half the number of chips to remove, erase, reprogram, and reinstall seemed like a good thing.
Posted by: Bolle on 2020-11-23 21:13:43
Again, why not read the original ROM chips in your ROM burner set to 27C400 and compare the contents to the ROM file you got from the internet?

Still 99% certain your ROMs are not the problem here. There is a checksum test early in the boot process, if your ROMs were bad that test would fail and you would not make it to the flashing question mark.
Posted by: Alexandre on 2020-11-24 05:30:16
Again, why not read the original ROM chips in your ROM burner set to 27C400 and compare the contents to the ROM file you got from the internet?

Still 99% certain your ROMs are not the problem here. There is a checksum test early in the boot process, if your ROMs were bad that test would fail and you would not make it to the flashing question mark.
Sorry i did not answer on this... I compared my roms vs the original and the code isnt exactly the same... overall there is some similarity but not exactly the same and the compare test alway fail BUT... for testing my original rom i have to chose a "device" on my programmer software and i used the generic 27c400 to dump the rom but i am not even sure that this is the correct device for dumping thoses original roms. This is why im focusing asking if thoses 27c400 are the same pinout than the original roms
Posted by: Alexandre on 2020-11-24 05:32:02
You should be able to use it without the rom card, just don't use the modified system rom. You can always email @bbraun.
Thank! i ordererd some 27c400 as i only have 1 in stock yet... as soon i received it and test it i will let you know here if it working
Posted by: Alexandre on 2020-12-14 08:14:59
You should be able to use it without the rom card, just don't use the modified system rom. You can always email @bbraun.
Hi

I finally received my 27C400. While i was waiting my order i emailed bbraun but i think he is not active anymore here as i did not received any reply. But anyway i can confirm that following his directive and using his tools and original stock rom i was able to repair my mac. I can confirm too that i previously had the question mark on screen with the defective rom but the computer was not able to boot from any device... Soon i putted my new burned rom the computer was able to boot correctly. So thank everyone for your help
Posted by: cheesestraws on 2020-12-14 08:19:54
That's good news.  Glad it worked.  I didn't know a dodgy ROM could do that; now I do!
Posted by: Jockelill on 2022-12-27 11:28:17
Reviving Athis old thread since I have a similar problem. I accidentally destroyed the two original ROMs by putting them on pin left… so they are fried.

I do have a programmer, and it looks fairly straight forward to make new ones. However, It says here that you need “100ns and faster”. I have however not been able to locate 27C400 chips of 100ns. I can find 120 and 150, but not 100. So where can I get those?

And does anyone already have a spliced ROM for HI and LO?

Joakim
Posted by: MaCJaX on 2023-11-22 18:45:02
Hey @Jockelill. Did you ever fix your Mac? I am having an issue that points to my ROMs and looking to burn some replacements. I found 27C400-105DC ROMs that I would like to try as those are the fastest I can find. Anyone know if those will work? Thanks in advance.
Posted by: Jockelill on 2023-11-22 22:00:12
Hey @Jockelill. Did you ever fix your Mac? I am having an issue that points to my ROMs and looking to burn some replacements. I found 27C400-105DC ROMs that I would like to try as those are the fastest I can find. Anyone know if those will work? Thanks in advance.
Pretty sure those should work. I designed a PCB instead that uses modern chips (and covers both slots). With this I have 4MB ROM space. I haven't gotten to try anything else than stock ROM on it, but will when I get more time.

1700719118720.png
The major benefit is that this I can program in the normal ROM SIMM programmer. If you are in EU I can build you one, but if you are in the US or elsewhere, you can send a DM to @WillJac instead 🙂. He also has them.

Joakim
Posted by: neongod on 2024-03-18 02:17:02
My Classic II had faulty ROMs, so I had to make new ones. Earliere the cheapest EPROM programmer available in the EU was the TL866-II (most online guides and youtube videos are about this one), which was unfortunately discontinued. I ended up getting an XGecu T48 programmer, which is the new version of the TL866-II, but it's incompatible with the old adapters due to the socket facing the other way. Luckily there is now a compatible 27C400/800/160 adapter.

I used AM27C400-105DC DIP-40 EPROMs I bought on eBay. The ROM file found online can be splitted with the small C program linked above, but if you don't want to compile it, here are the two parts I splitted: 341-0257-mod.bin, 341-0261-mod.bin. I made a post about how to burn them with the XGecu Pro software on my site, hope this helps someone to revive their Classic II.
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