Starting testing of logic and amplifiers in drive B

SCHEMATICS OUT OF SYNC WITH THIS DRIVE

The book of schematics I own are a match for cabinet A, both the drive and the integrated control unit, but I found noticeable differences in the cabinet B boards. If I have to debug or repair any of the boards that differ from the diagrams, it is going to force me to compare and partially reverse engineer.

One example was the operator control board, which had some additional ICs and a hand executed engineering change that involved cutting board traces and a jumper wire. That one was a simple board and not many changes but still took 30 minutes of tracing before I was sure I had found all the changes.

SHORT TESTING OF LOGIC CAGE BEFORE APPLYING POWER

After inserting all cards in the logic cage, I used the VOM to test for any short circuits before attempting to energize the power supply. With that successful I could move forward to fire up the system.

VERIFICATION OF DRIVE SPEED CONFIGURATION

Boards 7, 9, 10, and 11 have configuration differences depending on whether the drive is to operate at 75 inch per second or the full speed at 125 ips. I verified that boards 9, 10 and 11 were properly set. However, board 7 has a problem.

On board 7 the specific part values for the configuration are all encapsulated in a DIP 16 package that plugs into the U27 spot on the PCB. This provides six resistors and two capacitors to the rest of the circuitry on the board, which is the pre-amplifier that controls the capstan motor. The package is missing, thus my board can't work as it sits.

I have the proper values and wiring required, thus I can build the parts onto a DIP socket and install this onto the board to complete its configuration. I won't be able to have tape move forward or back, nor read nor write, until this is completed.

INITIAL POWER ON AND OBSERVATIONS

With the boards installed and everything wired up , I applied main power to the drive power supply. Many of the PCBs in the logic cage have small red LEDs which illuminated and the fans for the +45 and -45V supply came on. No fuses blew or breakers tripped.

The operator control panel had the Power and File Protect lights illuminated. No button presses changed anything. I believe that I will need to place a tape on the drive before the logic will attempt to load - firing up the vacuum/blower motor and rotating the reels trying to thread the tape end into the vacuum column and through to the take-up reel.

CLEANING TAPE PATH

I chose to clean the tape path at this point, using lab low-lint wipes and 99% isopropyl alcohol. There was a lot of dust picked up but finally I am ready to try to fit on a tape reel and test out the loading sequence.