Wednesday, November 8, 2017

Working on HPdrive emulation, 2262 terminal connector, 7906 alignment plan


I repaired the 001 manual keypunch, after a linkage for the space key had fallen off somehow. It was good that we got it back into service as we had a school visit where the fun activity for the kids was punching cards on the 001 and on the 026 powered keypunches.

Iggy worked on one of the tape drives that tended to flutter the tape in a vacuum column up and down near the bottom, also causing the reel servo motor to hunt around trying to follow the tape position. The problem was in the vacuum activated switch, which had an up and a down set of contacts. 

The two sets of contacts were almost overlapping in operation, fighting each other moving the tape up or down. Iggy bent one set to provide a wider zone where neither was active, thus introducing some hysteresis that settled down the drive. Now, the tape jumps up and stops properly, with the reel motor stopped as well. 


HPdrive disk drive emulation facility

My PC arrived today, that should have allowed me to configure the NI HP-IB card and install the HPDrive software. To make use of it, I still need to:

  1. receive the 12821A card for the HP1000 that acts as a disk controller
  2. hook the cable between the HP1000 system and the PC
  3. test booting with my current bootrom
  4. burn a replacement ROM with a different boot loader if needed

To my surprise, the HP 8000 desktop unit was actually their Ultraslim type, meaning it has zero PCI slots. A waste, although I will put it to use somewhere else. I found a desktop locally that will be delivered tomorrow, one that has 3 PCIE slots. 

7906 disk drive repair

To complete an alignment of the 7906 per the HP service procedures, I need the following:

  • alignment cartridge
  • disk service unit
  • 50 wire ribbon cable
  • alignment printed circuit card
  • 20 wire ribbon cable
  • special preamp printed circuit card
  • head/index transducer alignment tool

I have the first three items. The fourth, the Head Alignment PCA, was quoted at $300 from one person who owns it. The fifth, ribbon cable, is easy to make. However, the sixth, special preamp PCA, is unobtainable as far as I can tell. Without it, the other parts won't work. I am loathe to sink $300 further with no guarantee I will get a full operational tool.

In the service manual, there is a diagram that shows oscilloscope probe points and waveforms for alignment. Unfortunately, these are the servo waveforms that will tell me that the positioning logic believes it is directly over the cylinder on the servo track.

Scope patterns for servo head in alignment, but not the data head above
They do NOT show me the probe points and waveforms that would be seen on the read/write head for the removable cartridge at the same points. I need to see this to tell if my data head on the top of the removable platter is directly over track 245 while the servo is locked on 245 on the lower platter.

For alignment to be possible without the special printed circuit boards, I will need to see a recognizable pattern on the lower data head of the removable platter, assuming that it is properly aligned and the drive is out at cylinder 245. The upper head must be adjusted to recreate that pattern I will see. If it is too ambiguous or I can't make out a pattern to use, then alignment will not be possible.

2262A terminal cable build

The male Centronics 50 connector arrived today, allowing me to complete the conversion of my existing serial card cable to a version that will fit properly on the 2262A terminal. BTW, these terminals are called the ET type because the silhouette looks like the alien from the ET movie.

After soldering the connector onto the cable, I did a test using the tape diagnostic program to write to the terminal in conversational mode. No response, unfortunately. I will need to look at the wiring inside the hood of the connector, as well as the configuration I set up in the terminal. I imagine that something doesn't match. 

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