Disk heads cleaned and reinstalled on the IBM 1130 internal disk drive, but too rough to be used

CLEANING HEAD SURFACES IN PREPARATION FOR FIRST ATTEMPT TO FLY ON PLATTER

The heads must be completely clean, free of any oxide or other buildups on the surface. These will be pushed down onto the spinning surface but will fly above it on a cushion of air about 125 microinches thick. That is produced by the air being dragged by the disk surface as it speeds under the head at around 45 miles per hour. 

Any imperfections on the disk surface will affect the air cushion and potentially apply a torque on the head which causes a portion to ride lower than the target height. Worse, if the oxide or other foreign objects on the head are larger than .125 mils they will touch the disk platter surface. 

This is in addition to the need to avoid dust, smoke or other particles in the air inside the cartridge that are on the large enough to jam between the head and disk platter, driving it down onto the surface. In mild cases this causes short light scratches on the surface and the head resumes flying. However, it can dig into the oxide surface and result in the head scraping along producing serious platter and head damage. 

I use 99% isopropyl alcohol (which of course has absorbed atmospheric moisture and is not really that pure when applied) with wipes that don't shed lint. The goal is a really clean head surface with no particles at all on the face, as verified under the microscope. 

Once I finished, the heads are just too scraped up to safely be lowered onto the disk surface. This drive will have to run with my virtual 2315 emulation facility which keeps the heads from touching the unused disk cartridge but otherwise spins the cartridge and moves the arms in and out, while serving data from the emulator instead of the disk heads. 

MAKING SURE LOWER ARM HAS THE PROPER SPRING BEND FOR INITIAL POSITION

The disk head is attached to a thin springy metal which allows the head to pivot in two directions. That springy metal is welded to a somewhat heavier springy metal piece that is screwed onto a thicker sturdy aluminum holder. 

The springy piece that screws to the holder should be pre-bent to hold the head up and away from the disk surface when the drive is stopped. A mechanism in the drive will push on the rear of the disk head to load it down to the surface, bending the springy piece. 

The lower head appeared to sit very close to the disk platter when it was stopped, which introduces some risk that it could be hit by a platter as a cartridge is pushed into the drive. Also, when the heads are unloaded they shouldn't be near the platter in case of vibration of the machine or other events. 

I got everything put together and sitting at the correct spacing. I spun up a cartridge with the drive modified only so that the two pivots that push the heads down on the platter are removed. Thus, the head load solenoid will activate and the drive will believe the heads are down, but they remain safely above the surface. 

REPAIR OF HEAD CONNECTOR WHICH HAD BROKEN PINS

The connector from the cables of the disk head to the rest of the drive electronics has four small pins, male on the disk head side. Two of the four were broken and not making contact when I tested the circuit initially. 

I planned to repair them by digging out enough plastic around the male connector to expose a bit of the metal of the pin remnant. I can then solder the pin back onto the remnant, holding the pin in a surgical clamp with kapton tape to block heat transfer. If I could do this very very carefully I could restore the pin sufficiently to insert one time and anchor everything in place. 

However, the heads are not going to actually be used to read and write, since they are not safe to fly 125 microinches over the spinning platter. I am going to make an alternate connection, just to allow the read/write circuits to see the impedance and current they expect. 

HEADS REINSTALLED IN DRIVE

The sturdy hold of the heads slides into a channel on the disk arm, up against a screw adjuster tip that controls how far it moves in away from the center of the disk hub. A clamp gets tightened to hold it in place. 

The head positioning is critical for reading previously recorded cartridges properly. Each track is spaced 10 mils apart and the actual data content is considerably narrower after the erase coil cleans away the outer edges of the signal. The head needs to be as close to centered over the center of the track as possible. 

There is an alignment process that achieves this, which I have written about in other posts. I won't need to perform this, since the disk heads are not actually accessing the disk cartridge inserted. The data is instead flowing to files on an SD card in the emulator I will attach to the drive.