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  Systems Group System 2900 by Bill Degnan - 05/15/2017 21:34
Systems Group System 2900 S-100 Computer
Pictured is a circa 1982/3 Systems Group System 2900 Business class S-100 computer system. Click image for larger view


Systems Group System 2900 S-100 Computer card cage
View of the burnt components on the DMB 6400 controller card. Click image for view of entire card cage.


This system burned out some caps near the voltage regulators of a card labeled DMB 6400. Otherwise the system seems ok enough to attempt a restore. I have zero info on this machine, but it seems similar to other S-100s of this era. More to come.

More photos

Systems Group Ads from Byte (System 2800, Dec 1981, July 1982)

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  repairs complete / Need Password by Bill Degnan - 09/02/2017 22:10
Systems Group 2900 S-100 System Measurement Systems and Control Inc I/O card repair
This photo shows the same "DMB 6400" card from above with repairs completed. Printed on this card is the label Measurement Systems and Control Inc. The new caps are orange not blue and as you can see I figured I might as well do all the 4.7uF 35V caps while I had the thing out. I also replaced the 7805 voltage regulator, which I believe was the cause of the blown cap(s) in the first place. NOTE: Photo was taken without flash and is appears yellower than actual. Click image for large view.


The system boots and displays the message above. Of course now I have a new problem, what's the password? Click image for large view.


I found a place where I can download a binary of the MP/M OS disk for a Systems Group 2800, should work for this machine as well.

http://www.cpm.z80.de/binary.html

Right now the computer boots directly into the hard drive, the disk drive is completely bypassed. I assume there is a switch setting somewhere that I can change to cause the system to attempt to boot from the disk drive first. If I can get a disk with MP/M to boot from the diskette drive I can potentially find a backdoor to the password file used by the "Temple University Career Development Computer System" . If that fails, I can attempt to get the password from RAM by using an in-circuit emulator installed into the Z80 CPU slot. By observation I believe the password test program puts the password in RAM after the first attempt. It does not appear to check the hard drive for the password when you try a new password after the first attempt fails.

Lastly, I cleaned the internal dust and a little gunk from the front grill.

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