HP-7900A Disc Drives

We have 7900's (about 20) in use on test systems still. We also have 7905's and 7906's. I maintain them. The platter package that goes in the 7900 is not the same as for the 7905/6 models. The outside casing looks the same, but the platter for the 7905/6 is about twice as thick as the one for the 7900 drive. Plus, the disk pack for the 7900 Drive has 24 hard sectors as indicated on the bottom of the platter. The 7905/6 disc pack has one notch on the center hub which is used for a soft sector configuration. Do not put the 7900 disc pack in the 7905/6 or vice versa. Michael Morar PS - I need some info on the A2 board of the HP-7900A disc drive. The A2 board has special solder terminals mounted on the board for connectors J1 and J4 thru J7. I need to find out who makes them. HP no longer has any info on the drive, and our service manual does not have a break down of these pins.