Friday, October 13, 2017

Friday session at Marc's involving several machines


I hooked the tool up to the third Diablo drive we have, one loaned by Al Kossow to allow us to copy disk to disk. It was not able to make the terminal seek.

Since the tool works great on the first drive, stutters with delays  seeking on the second drive (one inside the Alto), and does no seeking on the third drive, there is some difference with electrical characteristics to explain this. I will need to test this carefully with scope and possibly logic analyzer until I find the reason. 


We hooked up the third drive to our Alto, setting it to unit 2. Our plan was to use the drive to read and archive the cartridges from Xerox PARC, while we retained our unit 1 drive for use with our Alto cartridges. 

We did this because the first drive has some residual disk crash contamination on the heads from one of the PARC packs being read many weeks ago. As it is likely that further crashes may occur with many dozen cartridges to archive, we wanted to protect our basic Alto ability by sequestering the PARC packs to drive unit 2.

We began archiving content, using the copydisk function to the LCM provided networking bridge from our unit 2 drive. We completed archiving a number of packs, but then one of the cartridges began encountering hard errors right away.

We removed that cartridge, read another one fine, then near the end of archiving another one we encountered another hard error. At that point we opened the drive to inspect the heads. The lower head had some oxide packed into the gaps in the head, so we cleaned both top and bottom heads.

While the lower head now looked fairly clean, when we inspected the upper head using a mirror we could see quite a bit of oxide and clear signs of a crash. We opened that last pack and found some rubbing marks consistent with a crash - not so deep that the aluminum substrate was visible, but too much to risk mounting the cartridge again.

Our plan is to remove the heads from the drive, clean them well with the aid of a stereo microscope until we are positive they are as good as new, then reinstall them and align them using the disk alignment cartridge loaned to us by Bruce Damer.


Ken continued to QA test the ethernet tool, passing everything except for some problem that occurs only with copydisk but not network boots, ftp, or the many other protocols used with the Alto. He collected some data and will be examining the code and data to resolve this for our next session in a week. 

Ken also designed a PCB to make the ethernet tool much more rugged - he should receive the manufactured boards in about a week. The goal is to have the rugged version, built into a case, and in steady use before the end of the month when Al will need the LCM box for use back at CHM. 


Marc was able to repair a external 20MB hard disk for use with his Mac 512 and SE/30 computers, a journey involved failed power supplies, microcontroller chips, disk failures and transistor suicide. 

We also worked on a few problems with an HP 7970B (800 BPI 9 track tape drive), including the begin/end of tape sensor and idler roller. 


At one point while Ken was debugging the ethernet tool, he would switch back and forth by unplugging the tool from the Ethernet port of the Alto and plugging in the transceiver box that connects to the 3Mbit cable. After one such swap of cables, with power off, we turned on the Alto to find the disk drive displaying the Check error light. 

We powered down and back up again to see if it was a transient issue, but upon power-up of the Alto the disk drive was completely off. I pulled out the chassis and saw that both +15V and -15V supply lights were out.

We opened the unit, found both fuses good, and began a binary search for the problem by disconnecting both ethernet transceiver and disk drive. The two supplies came up fine. We connected the disk again. It came up fine. We added the transceiver. It came up fine. No problem and no explanation for what 'fixed' it. 

We saw a partial repeat much later in the day, when after some swap of ethernet port connections we powered up to find both unit 1 and unit 2 disks with the Check lamp lit. The power supply LEDs showed us that the -15V supply was off. A power cycle made everything happy again.

We believe we have an intermittent problem that will become more pronounced or fail permanently in the future, but have no clue yet about the transient cause. 


I have traced and verified the connector pins on the monitor back to the ICs from the schematic. I now have verified that my keyboard and monitor side pin assignments are correct, the keyboard works properly (based on yesterday's test), and thus my problems using the keyboard with the monitor could only be:

  • Monitor circuitry is faulty, not emitting row/column addresses and latching in key status
  • Incompatible combination of extended keyboard and 2622A monitor
  • Some flaw inside my cable between the two connectors

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