Mac Plus strange boot up issue

[CharlieFrown]

Hi I bought this Mac Plus with ROM error ( probably needs freshly burnt eeprom ), but I tried to swap ROM chips from 512Ke (seated inside MacSnap scsi card). They should be compatible with Plus. 

When booted it with new ROM it showed happy Mac and started to load from floppy, but it stops after several seconds of disk reading (I can hear normal floppy reading sound). 

I thought the internal floppy drive was broken, so I tried external drive, but it was the same thing - chug, chug for several seconds, then nothing on screen. No clicking floppy sound, no error. Same thing with different floppies with System 6.0.8.

When I used the same ROM with 512Ke, the same external floppy it booted System 6.0.8. smoothly with each floppy I prepared.  I am completely confused. What do you think?

 

[tjjq44]

Maybe something else in the hardware of your mac plus, broken trace or component?

What happens if you put the original roms of your plus in your 512ke? If it boots fine with them your plus mainboard may have a problem... Try it with different ram simms too

 

[CharlieFrown]

tjjq4: Mac512ke shows sad MAc 01Exxx error with swapped ROM chips from Plus. 

Is it worth trying to dump original ROMs from Plus and write them to 27c512 chips? I think I've heard about this solution, but seems dubious in my case.

 

[tjjq44]

Ok, Rom is surely the disease... try to borrow "known good" plus roms from a friend and try them in your macs, if everything goes well then you'll just have to either dump them or buy one from BMOW

 

[Elfen]

The Mac Plus and the Mac 512Ke are the same ROM image.

Given that, if you can copy the ROM to fix the Plus, then by all means, do it. If I am correct, they are 64K ROMs so a 2564 or 2764 should work (I remember doing this with Dr. Levinson on upgrading old Macs long ago)...

As for the floppy, I suspect the Bournes Filter at the floppy ports or the IWM Chip. Compare the IWM Chip on the Plus with the IWM on the 512Ke, they should have the same chip number.

 

[CharlieFrown]

thank you Elfen and tjjq, I will have another Plus (labeled Plus ED), so I can check those things. Will give you an update.