Saturday, August 15, 2015

Still cleaning Pertec disk head before returning it to service; working on SAC Interface Box


I fired up the microscope and examined the cleaned disk head to see if there are any protrusions, scratches or chips that could disturb the airflow that is essential to the head flying properly above the platter surface on its 125 microinch cushion of air.

Pertec head with crud inside slot but undamaged rim and undamaged head poles
Leading edge of head is undamaged, just a bit of soot, and head slot undamaged at top

The edges of the head and its surface is almost totally clean. I did see a couple of raised spots which I have to continue to clean, as these would be candidates to cause a head crash if they remain. The leading and trailing edges, and the entire rim of the head, are clean from damage.

Raised anomaly at top left of light blur
Raised anomaly at right side near edge
The slot for the erase and read/write head poles don't have any dings or raised sections at the head surface, but are still a bit dirty with residual good compared to my sample of a good head. There are a couple of pictures that lead me to believe this head slot can be cleaned satisfactorily.

Head slot with residual gunk but crisp edges

Slot of an undamaged but similar head for comparison

I included a picture of a metallic slider from a Diablo drive that suffered a crash, with clear scratches on the surface that render the head unusable. By comparison the Pertec head sustained almost zero damage. I saw a couple of anomalies which look like raised crud on the ceramic surface - if these can be fully removed, I will be comfortable returning this head to service.

Now this is a crashed head (from Diablo drive)

I fired up the interface box to resume testing of the virtual 2501 card reader capability, but found that the pesky, fragile connections for inbound signals to the 1130 are acting up again. I am not happy at all with the quality of the connections and will be thinking about possible modifications to make it more robust.

Meanwhile, I have to find a way to create memory images of various important programs, such as diagnostics, so that I can just load them into core and start up. Otherwise, there is a process of step by step bootstrapping which involves decks of punched cards, a somewhat tedious process.

The normal workflow to run a diagnostic, for instance the keyboard/console test, is to put the relocating loader deck in the card reader hopper, followed by the Diagnostic Monitor II deck, followed by the test(s) in question, followed by a blank card. The Program Load button causes the first card to be booted into memory, after which the program reads in the loader and then the monitor and finally the tests.

Without a physical card reader, I could do this one of two ways. The first is to convert the first card of the relocating loader into its memory contents as if it were entered by a Program Load but the machine was kept in Single Instruction mode so nothing executed. This could be placed in storage by my 'load core from file' function. When this program is told to run by setting the IAR to 0 and pushing Program Start, it will attempt to read further cards from the 2501 card reader.

My virtual card reader would have a PC file containing the rest of the relocating loader, the diagnostic monitor and the keyboard.console test plus a final blank card. I would tell my interface box to load a binary file into the virtual 2501 reader, after which it 'should' read everything in and begin executing the test.

A second way would be to stack up the decks in the IBM simulator program on the PC, boot from the card reader and have the decks read in and begin execution on the simulator. At this point, with the test poised to run, I can dump the memory contents into a file which can be loaded into core by my interface box. I need a machine configuration that matches my intended hardware, in particular it needs a 2501 card reader, plus I need the binary decks for the 2501 relocating loader, the diagnostic monitor II and the keyboard/console test.

I have the decks for the diag monitor II and the keyboard/console test, which I can read in using my Documation card reader to create the PC side files. I am not sure if I have the 2501 relocating loader deck - if not I have to make use of a copy from the IBM simulator or assemble a deck. Finally, I need to boot in the one card of the relocating loader into core, in single step mode, to create the core image for use on my real hardware.

My real 1130 came with a 1442 card reader, not the 2501, thus I don't have a bootable deck of a 2501 relocatable loader. I made an attempt to boot the stack of the 1442 relo loader, the diag monitor II and the keyboard/console test into the IBM simulator, hoping to create a usable core memory load from that.

Somehow my interface between the Documation reader and the PC program is not working - the USB device is not showing up as a serial port. I tried it on two different PCs, but ran out of willingness to debug this further. The reason - it is in the upper nineties right now and the card readers are in the datacenter shed, which does not have air conditioning. Too brutal to stay in there for an extended period. I was willing to nurse a small card deck through, but that was all. This will wait for tomorrow. 

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