12285Workin' on the IMSAI...
- Apr 20, 2009I've finally had a few more hours to work on the IMSAI, and things are
looking up. After slowly bringing up the electrolytic capacitors in the
power supply to their rated voltage (in stages, monitoring the current), I
left them sit there for several hours. After bleeding off the charge, I
put everything back together and powered up the machine with only the
front panel plugged in. No smoke!
Next, I plugged in the Cromemco ZPU card, the Fulcrum Omniram 64KB
static RAM card and the Compupro active terminator card. I tried the
Deposit and Examine switches, but was getting inconsistent results. After
some online reading, I decided to disable the Power On Jump (POJ) on the
ZPU card. Now, the Deposit and Examine switches were working as expected.
I toggled in a short program, found here:
All it does is move an LED back and forth in the Programmed Outputs
register on the front panel, Cylon-style. You can change the speed by
turning on the high address switches. It worked:
The next step was to insert the Morrow Disk Jockey 2D/B floppy
controller and connect the dual 8-inch drives and a serial terminal. The
2D/B has its own POJ logic, which sends the CPU to F800H on reset. No joy
on booting from diskette, though. From the front panel, I can read the
jump table at F800H and can follow the program flow. The red LED on the
2D/B comes on indicating the controller is ready, but the drive select LED
doesn't pulse as described in the manual. At this point, I ran out of
time. I'll pick it up later and try to figure out if the drive is
Mike Loewen mloewen@...
Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
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