Monday, October 28, 2019

Start testing logic and power amplifiers in drive A


I did a quick check of the power supply connectors to see if any of the loads are shorted, using the VOM to measure resistance. All the results were reasonable except for the 12VAC line which appeared to be an open circuit. There may be a relay that connects this line only at certain times; investigation is needed.


Since I am still waiting for the fuse holder for the cabinet A power supply, I swapped the power cables over from the A drive to the B cabinet power supply. Too, I moved the vacuum and pressure hoses over to the A drive, giving me a complete unit to test.

The hose lines and power cables are all a bit short, so that I could barely get them connected across cabinets. My first attempt looped the hoses over the mid level frame bar, which wouldn't permit the two drives to be pushed together.

The power cables required that the cabinets be abutting, thus I had to redo the hose connections. I completed all the connections and slid the drive cabinets together. Everything fit together with no slack but not excessively taut.


Power up was done with no circuit breakers tripping or fuses blowing. The operator control panel had the Power, File Protect and Load Point lights illuminated. Load Point was weakly lit, unlike the others. When I pushed the Load/Rewind button, vacuum power came on, the automatic cartridge opener activated and the drive was trying to thread tape into the vacuum columns. After a short interval, Load Check illuminated which is expected.

When I push the Unload button, the power window on the front door lowers. Hitting Reset or Load/Rewind will raise it again. This is as expected.
Power window in front door lowered

I opened up the vacuum chamber on the drive and cleaned it thoroughly using Isopropyl Alcohol and KimWipes. A lot of dust had coated the walls, faces and other parts including the tape head. It had to be removed before I would attempt to load tape.

Vacuum columns, head and tape transport path

I couldn't figure out how to get the tape cartridge inserted with the tape seal in place, so I removed the seal and put the tape on the drive. Hitting Load/Rewind starts the vacuum and begins slowly rotating the tape reel counter-clockwise. This continued for some time until the time-out when the control logic declared a Load Check condition.

The control logic for the drive sequences through state machine steps to load the tape. The first step is to power on the vacuum and blowers as well as the +45/-45V supply. This also activates the automatic cartridge opener which should open the wrap-around seal and lift it to give access to the tape.

The second step rotates the tape counterclockwise until the end of the tape closes a vacuum switch that indicates the end of tape was located. This should advance the machine to the next steps where it will turn the tape reel clockwise and feed the tape down through the vacuum columns, tape heads and eventually onto the take-up reel.

However, the drive never advances. This will require some diagnosis to determine if the flaw is in the vacuum sensor or the control logic board. Very fortunately, I found a binder in the garage with the maintenance manual and other helpful documents. Just in time, too!


  1. Load Point weakly lit at power up
  2. Fails to load tape

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