Testing my new seek logic for the Virtual 2315 Cartridge Facility - part 9 - Fixed cylinder 202 issue

ADJUSTING THE FORWARD CRASH STOP ON THE INTERNAL DISK DRIVE

Crash stop when arm is not at 202

Arm against crash stop just past 202

In order to be safe, I changed the stop to a gap of .008", giving the maximum margin for acceleration while still blocking the ability of the arm to move to cylinder 203. With an attempt to move 20 mil, the arm should stop and the detent should still fall back into the notch for cylinder 202. 

Just as importantly, it should not do anything bad if it gets a 10 mil step thus engaging the odd detent instead of the even detent. Looking closely at the positioning rack, I can see there is a notch at the 203 location which the odd detent can enter. 

The way you read the location is to look where the right detent is pointing. The numbers are etched every 40 tracks, with a large vertical bar at the 20 track intermediate point. The fine vertical lines on the positioning rack mark each 4 track step, with a notch in between at the 2 track point. The left detent (odd) will fall in to indicate that the location is the number you read from the right detent plus 1. 

The picture is of the arm when I had a .006" feeler gage between the crash stop and the arm, the arm not quite far enough along to let the even detent fall into 202. However, you can imagine the rack slightly to the right so the right (even) detent enters the 202 notch. This is where the arm stops at the last legitimate location. 

If we attempt a 1 track (10 mil) step forward, the drive flips which detent is used to stop, now engaging the odd (left) detent. Since there is a notch there that the odd detent can enter, it will try to hold the arm there. That means the drive is trying to be at 203 but the mechanical stop is trying to keep it from moving past 202. 

It may be slightly mispositioned to read or write on the cylinder but it is a reasonable state to stop in. As long as the circuitry in the disk drive turns off the acceleration of the arm so it doesn't lock up buzzing, this is a decent outcome. It will back up correctly. A step of 10 mil will bring it back to 202 with the even detent engaged, a 20 mil step will move it to 201 still using the odd detent. 

The IBM maintenance manual blithely instructs the field/customer engineer (CE) to run the drive, use the CE switches to move the arm out to cylinder 202, then adjust the crash stop to a specific gap. The stop is a bolt that is threaded into a big block holding the arm mechanism together, with a nut that locks it in position. 

The issue is that the slot in the bolt that one turns to adjust the crash stop is directly against the 2315 cartridge case that is in the machine. There is no room to fit a tool in there to turn that once the nut is loosened. If I remove the cartridge, the drive will not spin up nor load the heads, thus it wouldn't allow arm movement or perform seeks. 

However, I can manually push the microswitch that detects a cartridge is inserted, to allow the drive to spin up and load the heads. They won't really load for two reasons - no platter to ride on, but more importantly my modifications have stopped the heads from being pushed down so they will remain safely apart 

I did find a way to use pliers to turn the threads of the bolt after loosening the nut, thus could adjust this with the arm actively sitting at 202. The gap was much too small, so I adjusted it out to a suitable amount that would stop the seek action but not move past 202. 

TRYING TO MOVE THE ARM PAST 202 AFTER MY ADJUSTMENT

The disk drive is designed so that if the cable that plugs into the drive from the controller (or from the 2310 Interface Board in our case) is removed, the Customer Engineer (CE) switches and buttons can control arm movement without having to issue XIO commands or involve the 1130 disk controller logic. 

I moved the arm to cylinder 201 from zero by setting the Step switch to 20 Mil and held the switch at Continuous movement until it got close. I then set the Step switch to 10 Mil and advanced one step at a time until I verified that the arm reached that point successfully. This would have the odd detent in the rack.

I then moved the arm 1 track, with Step set to 10 Mil and using a single advance, which should put the arm at 202. That was verified by looking at the arm . The even detent should be engaged.

Now, the moment of truth. I issued a seek of 2 tracks farther, with Step at 20 Mil and a single movement request, which should leave the the arm at 202 and the drive should recover from the attempt to move past. The even detent should remain engaged. Worked great.

I cycled the drive to get the arm at the home cylinder and used 20 Mil steps to advance the arm to 202. I moved 1 more track, with Step set to 10Mil, wanting to see what happens with the detents and the arm. I looked at the detent and the arm position, as well as the V2315CF. If the odd detent is now engaged, a reverse step of 10 mil would actually stop the arm at cylinder 200 instead of 201, which is not desirable. If the even detent remains engaged, I need to understand the mechanism.

After testing and observation, it does engage the odd detent, but has bounced back to 201. I hooked up the system and did plenty of seeks, with the pathological behavior gone. This problem is now resolved.