No time to make a Web page now, these are my notes, images later.
This Ithaca DPS-1 8-inch drive system is discussed on my Ithaca DPS-1 restoration Web page of Mar-April 2016 - herb
Mar 28 - cabinet opened and examined. ith_drive_cab.jpg Ohms tests on DC power lines shows no shorts. Cabinet in good shape. Lubricated Shugart 801 drives, cleaned heads (single sided one head). Slowly rotated hub to release belts from adhesion. drive jumpers, hub accessable from bottom ith_drive_access.jpg INspection of connnectors showed a loose +24 on one connector. One AC motor connector showed black damage as if intermittant and sparked. ith_drive_pins.jpg Power applied by Variac. Power supply (open frame non switcher) slowly raising voltage during 15-20 minutes. AC motors on drives a little squeaky but OK, occasionally whistles. DC power seemed OK on +5 and +24 at full AC voltage. But -5V supply erratic. removing and connecting DC drive connectors showed negative supply depended on load. Voltage varied from very low to a few volts negative. Tweaking apparent pot did not produce much result (in case pot was corroded). ith_drive_minus.jpg Circuit appears to be uA723 regulator without pass transistor. Had no schmatic on this generic (Power one?) power supply. I have a physically similar suppply from another cabinet, may substitute. Downloaded from Web the uA723 data sheets. Probed circuit to trace connections. It will be hard to remove the regulator circuit board from the power supply. I determined later, I was wrong, there WAS a pass transistor. Mar 29 - DC measurements of uA723 and pass transistor are below. Measured relative to common (ground) output pin. Voltages varied during time of measurements. Measured no-load "cold", followed by "one drive" load. no load, supply output -4.7VDC, 1 4.4 14 0 2 4.4 13 2.53 3 0 12 2.64 4 0 11 2.64 5 .91 10 .78 6 .93 9 *AC* 1.7V 7 -4.78 8 2.64 Q2: Coll 4.79V, emit .24 base AC 2.2v one drive load, supply output -2.54VDC 1 .54 14 0 2 .54 13 2.5 3 0 12 2.6 4 0 11 2.6 5 1.1 10 .77 6 1.02 9 *AC* 1.2V 7 -2.54 8 2.6 Q2: coll 7V, emit .26V, base AC 1.0V The collector voltage looked so odd, I did a diode check of the power transistor in circuit. That did not look good either (should be .5-.6V forward, no reverse current, for emitter-base and base-collector junctions). If the power transistor failed, that's an easy repair. So I removed the p/s from the case (but did not unwire it) and removed the power transitor for -5V. Diode check out of circuit showed 1V from emitter-collector. Transistor was a 2N3555, easy replacement. Installed a new 2N3555 and tested p/s. Produces steady -4.55V with zero, one or two drives. Close enough to -5v. Drive testing ------------- Tested drives on Ithaca DPS-1 and worked! Booted up CP/M! ith_drive_first.jpg But.... some odd effect, had trouble with B: drive. So I swapped DS1 and DS2 jumpers on the drives, tried again. Booted other drive OK. Did more tests. Drives are set up so both heads are loaded whenever either drive is accessed. But drive select light is only active on drive in current use, head only advanced on active drive. ith_drive_tests.jpg Various tests showed some hesitancy on the left-hand drive in case. Seemed to need the mechanical drive-latch lock to be exercised, to reboot. Otherwise would hang without booting, only lit A: drive light (left hand drive). I noticed squeezing the drive latch, somewhat affects the position of the of the index hole sensor. No index would stall the system. So I reached in and wiped the index sensor with my finger. That seemed to solve the left-hand drive's problem for awhile, but it comes back from time to time. Again, if I "squeeze" the hard drive latch to engage it tighter, the drive seems to become active - I'm still guessing the index sensor is associated. Before and after this issue, drives worked OK. Run program on one drive to access another, produced rapid drive selection without program stall.
Copyright © 2016 Herb Johnson