Thursday, July 16, 2015

Pertec drive loading heads on disks successfully, DOS/VS sysgen proceeding

Work was quite heavy and kept me from the workshop for all of yesterday but I wrestled some time free to play around at lunch time and in the evening.


I prepared my supervisor assembly deck today, selecting the options and configuration I wanted. I wrapped it in JCL and brought it over to submit to my DOS/VS system under Hercules. After discovering one tiny typo - an extra space on an assembler statement which pushed the statement continuation character out of column 72. Mainframe systems were often highly sensitive to specific positioning - things had to start in a given column number or the code wouldn't assemble or compile.

I then finished my supervisor assembly, linked it into the core image library,and did an IPL to test out the new supervisor. Unfortunately, when I entered the supervisor name, the IPL failed with a compatibility error 00. Whatever that is. Time to dig through the various manuals to figure this out.
I also looked through the 'printer' output when I assembled and linked the supervisor.


A fellow vintage computing enthusiast has been helping me with documentation and advice on the Pertec drive. I had been a bit hampered by the existence of a board installed over the voice coil arm positioner, labeled as a timer board, that had zero schematics and only one cryptic mention in any of the schematics or other manuals I previously had. I know have information on this optional feature which will help me further in debugging and restoring my drive.

The main purpose of the board is to save energy. It monitors a drive for when it is idle without the cartridge spinning, turning off the +5V regulated power if the machine has been in that condition for 330 seconds. I never saw that behavior because I didn't leave the drive powered up for any longer than I needed for various tests.

My schematics for the drive seem to all reflect the changes that are made to connect to the +5V timer board, but no schematic of the board exists. At least I know how it was hooked in. Based on this, I could begin diagnosing my current issues. I made a list of points to monitor on the logic board, helping me figure out which condition is keeping the drive from lighting the 'safe' lamp.

After about a half hour of work, I now have the 'safe' light illuminating and the lock solenoid releasing. The unit seems pretty well healed now, so it is time to turn my attention to final cleaning of the platters and heads in preparation for first contact sometime in the coming days.

I cleaned the active area of the top of the fixed platter. I still need to get access through the bottom of the machine to do the same cleaning of the bottom of that fixed platter. Next would be the outer edge of the top and bottom since the heads have to slide through here to load.

When the fixed platter is done, the disk cartridge will need a good cleaning of its platter, top and bottom. Finally, the four disk heads must be cleaned and inspected to be sure they are fit to lower onto the platter surface rotating at 2400 rpm since they have to fly on an air cushion much smaller than a dust particle.

A prefilter and a HEPA-style absolute filter are ensuring that the air blown into the disk cartridge and fixed area are free of particles big enough to crash between the head and disk surfaces. I will vacuum them out and reinstall them. Once all these cleaning steps are complete, it will be time to get the drive to load up heads onto the disk platters.

I decided to fire up the drive and test the function that will shut off the +5V power after the drive is idle ("safe" lamp on) for more than 5 1/2 minutes. It did not turn off the power. This needs investigation.

I also have poor behavior of the lock solenoid. It should unlock as soon as the 'safe' light turns on, then lock when the drive starts a "run" cycle or when power is switched off. The light is on, but I have to wiggle the solenoid to get it to snap unlocked. Similarly, it is not very reliable in locking when the drive begins spinning.

I have the emergency unload bypass jumper installed, which ensures that the emergency unlock doesn't kick in and try to pull the disk arm back to its rest position. I also unplugged the voice coil itself, so that the arm won't try to move out and load the heads onto the disk platters.

I can verify that the drive spins up, then increases speed for thirty seconds to purge the disk of any residual dirt or dust particles, but at this point it wants to load the heads which I have blocked by my removal of the J205 cable to the voice coil positioner.

Once I had opened the fixed platter section, carefully cleaned the top and bottom of the platter, reassembled that section, I cleaned the platter in my disk cartridge. Last stop were the heads, which were cleaned and inspected.

I wanted to load the heads by hand - meaning get the platter spinning and then push the positioner out to put the heads on the disk and slide them along. I held the safety switch with no cartridge in the drive, so that I would only be loading the lower set of heads onto the fixed platter. It worked well, no problems and no marks.

Since the fixed platter loading was smooth, I inserted the cartridge and hand loaded both pairs of heads onto the two platters - just one positioner moves the heads to the same cylinder for both platters. That went smoothly.

 After everything looked good, I removed the emergency unload bypass jumper, plugged in the voice coil, and prepared to start it up. The drive sequenced itself up, spinning at 2400 RPM and then faster for 30 seconds in a 'purge' cycle which blows any residual dust or particles off the disk. Then, the position shot out, loading the heads on the platters. Very nice indeed!

The 'ready' light did not go on, but the heads remained flying at their loaded position, which means the drive didn't detect any error that warranted a retraction and spin-down. Since I don't have anything hooked to the interface of the drive, there could be a signal or two that are needed before the drive reports itself  'ready'.

It is time for me to re-install cable ties to keep the cabling neat and out of the way, since I had to cut apart the old ties when I was removing boards and heat sinks during my power supply repair project.
Debugging from here will involve some status checking using probes, then I will set up an FPGA to act as the controller and computer, allowing me to exercise the servo positioning, test the various commands, and get myself ready for the reading and writing testing that will come later.


I had built a clock, based on someones kit, that would display the hour, minute and second as decimal digits using Nixie tubes, flash the seconds with neon lamps shaped as colons between the three pairs of Nixie tubes, and with a Dekatron tube showing a rotating pendulum. When I completed it, I used some old Nixie tubes I had bought on ebay years ago, but there seemed to be problems with those.

I just received my shipment of NOS Nixie tubes made in the USSR, which I plugged and and fired up the clock. I did see the digits lighting as they should for a short time, but as I had the Dekatron cable plugged in reverse, bad things seemed to happen. The project went dark and the high voltage has disappeared (which is essential to light the Nixies and neon lights).

I will have to dig out the schematic, debug the board to figure out what damage I did and repair it so that I can get my retro technology clock working. The project is a filler activity, so I may wait a while before I get back to it.

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