PDP-1 project milestone

The PDP-1 Restoration Project is still far from complete, but we hit a major milestone tonight. When we last tried to run Spacewar, the sun and player ships would not display correctly, though the starfield and torpedos seemed to be fine. We ran the DEC instruction diagnostics and they failed on the shift/rotate test, though all the diagnostics had passed a few months earlier. This week we wrote a more specific diagnostic program and determined that left shifts and rotates of the I/O register were not doing anything, though right shifts and rotates of the I/O register were fine, and all shifts and rotates of the accumulator were fine. After a little study of the print set, we identified two system modules that could cause the observed behavior. We tried replacing one of them, a 1607 pulse amplifier. After replacing the 1607, our own diagnostic and the DEC diagnostic both passed. Some of the team wanted to go home without trying out Spacewar, but the rest of us nagged until they gave in. We loaded it, and it ran correctly. Spacewar on the real Type 30 display with long persistence phosphor is a thing of beauty! Some of the tasks remaining to be done: * build new Spacewar control boxes * continue repair/testing of Soroban console typewriter * adjust Type 30 display to factory specs (linearity is poor) * adjust paper tape reader sensitivity/threshold * diagnose & repair suspected flaky memory "module" 0 * voltage margin checks, run all diagnostics * install new belt and test BRPE tape punch Eric