For more information about NorthStar, and a list of manuals I have, check this Web page. There's links there to other S-100 pages. Thanks!
Here's a Northstar system I purchased and resurrected in 2006, at the Vintage Computer Fest - East at Infoage in Wall, New Jersey USA. I'll say more about it another day, but this is what it looks like and this is what I did. - Herb Johnson
Here's the chassis view.
Here's the CPU board, a Z80 of course.
Here's the NS floppy controller.
Here's the view of the motherboard bus and power supply.
Here's a closer view of the back of the motherboard, which contains serial and parallel I/O.
Here's a non-NS memory card, probably by Central Data, 64K of DRAM.
Here's a close view of the I/O card, including a resistor (second from the top) that almost got fried.
The system sat unused for years before I got it, and the floppy drives were not correct or working. I replaced both drives. I cleaned all the board's edge connectors. I tested each card with an ohmmeter to ground, at either side of each board's voltage regulators - that tests for shorted capacitors. I found a few and replaced them.
Next I did some powering tests on the chassis, to make sure the big power supplies were functional. They were. Then I put cards in one at a time, and measured the DC voltages from the regulators. Those were all good, they sometimes fail or shorts appear.
Then I connected a terminal, confirmed with a simple RS-232 LED tester that transmit and recieve were not crossed, and tried to get some activity. It took me a long time to see why I did not. Tracing the wiring of the serial port, I saw that the -12V was wired through a resistor to a pin on the serial connector, which on the cable eventually was set to GROUND. That put a lot of current through that regulator and resistor - which is why there is a "fried resistor" photographed above. Removing the ground brought the negative 12 volts back "down" from ground. I was able to hit reset, a NorthStar DOS disk booted in the drive, and I got a DOS prompt!
I'll try to write more about this, sometime.
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Copyright © 2007 Herb Johnson
