View Full Version : help needed with Micro Expander Model 1

January 4th, 2017, 11:39 AM
Hi all,

i'm new to the whole S100 experience. My main hobby are Apple II computers but i had the wish to try something new :-)

I bought a rare S100 system, that should be compatible to the TRS80 or SOL computer. The unit has 2k of 2114 type Sram (4 chips) for memory (it seems) and is configured as a single board Computer with a additional S100 bus. There are several chip sockets not populated but that seems to be normal (). As the PSU was external and not included, i had so search a bit to get the Voltages right. It takes 8V DC and 2x 18?V AC to convert the AC voltages to +/-16V DC. There is a 12V and 5V voltage regulator inside the case. I infused the 8V and 16V into the voltage rails of the PSU-PCB and the computer seems to start. It draws 3A at +8V and 0.1A at +16V but the system does not 'boot'. I saved the monitor-ROM (D2732) and char-ROM (D2732) as files and copied them onto new ROMs but i got the same scrambled text display. I swapped the Z80 CPU with another one (measured 3.57 MHz at pin 6) but i got no change. The memory seemed to be ok as well...
The text graphics on screen are 80x24 and are totally random (no change with or without CPU or Monitor)

EDIT: The 64k memory board is a Central Data 64k (http://s100computers.com/Hardware%20Folder/Central%20Data/64K%20RAM.htm)

I tried to contact Scott Ware from (http://www.corestack.com/machines/expander.html) but got no reply.

If someone with a bit of knowledge about Z80 systems from the early 80s could help me?

John Monahan has already pointed me to Debugging for beginners (http://s100computers.com/My%20System%20Pages/Debugging/Debugging%20for%20beginners.htm) and thats what i will go through next.


BTW: i sent an email to Lee Felsenstein as well :-P


January 4th, 2017, 04:47 PM
Scott Ware picked up that Micro Expander computer (free) in 1997,
from a local computer store near Evanston, when he was at Northwestern University.

The original Micro Expander computer was introduced at the West Coast Computer Faire in April 1981.
The company was based in Chicago with Mats Ingemanson serving as president.

January 5th, 2017, 04:18 AM

January 5th, 2017, 07:36 AM
I have analyzed the memory board and it deactivates 6k of its memory from E800h to FFFFh. The first page of the ROM listing states that the ROM starts at F000h. This means there is 2k of memory (the onboard SRAM) from E800h to EFFFh.


January 7th, 2017, 09:50 AM
BigNick has sent me another pic :-)
Shipping to Germany will be a bit pricy, but still within my budget. Im very thankful to BigNick.


February 15th, 2017, 02:31 AM