Resources
Wiki
Mac GUI – excellent description and some repair hints
Firmware, HD Diag tools, documentation
Hard Disk 20 was the first hard drive from Apple. It communicated over floppy disk drive interface and was quickly replaced by SCSI standard disks, like SC20 HDD.
Documents
Internals
Controller Board
Hard Drive
Rodime RO552 – thanks to the proprietary communication interface, this drive was manufactured for Apple only. This makes finding replacement drives extremely hard, as they don’t exist outside of full Hard Disk 20 devices.
HDD Board
Disassembled HDD Mechanics. Unfortunately the drive was in such a bad condition, that it was not possible to make it work.
Power Supply
Reassembly
Some Dirt
This drive was in a very bad condition, probably submerged in water for a long time. The electronic boards seem to be restored fine, but the disk drive could not be revived.
I actually work on retrieving a HD20 with platters removal.
So the workaround would be :
– head alignement using optical sensor arm position
– formating using Nisha Diag all tracks of Head 0
– writing / creating a spare table from working hard disk RO552
– checkin the self test
I cleaned up one of these photos to make an HD Icon (due to Apple’s recent failure). Is that OK?
https://froods.ca/MacintoshHardDisk20.png
One more cleaned up “icon”, if it is OK:
https://froods.ca/MacintoshHardDisk20_front.png
Let me know if you want it taken down.