The MITS Model 1440 was a electronic calculator kit first produced in 1972 before the Altair 8800. This calculator was capable of performing square, square root, and memory storage. It had 15 digit LED readout.
There were 6 integrated circuits ("ROMS") but Bob replaced the one marked FDY 360B-7006 with a modern equivalent he made himself(!). He also replaced at least one zener diode. He sent me a complete write up of the repairs and notes. Additional pictures and documents related to the 1440
GENERAL DESCRIPTION (from the Theory of Operation section of the manual)
"..The Model 1440 Calculator uses state-of-the-art MOS/LSI (Metal oxides substrate/large scale integration, MSI (medium scale integration, SSI (small scale integration), and discrete semiconductor circuitry. The calculator consists of three major areas: input, central processing unit (CPU), and output.
The input consists of an array of switches house in the keyboard. Closing one of the switches causes a "Start" signal to be generated, and the unit responds accordingly. .."
Input chip: 7014 IC
Register chip: 5001 IC2
Arithmetic chip 7002 IC3
Control Logic chip 5013 IC4
Control ROM chip 7006 IC5 *
Output chip 5005 IC6
* This was found to be bad - looking for a replacement!
There is an article about this calculator kit in the July 1973 radio electronics.
From Bob Grieb who restored this calculator:
Here are some photos for your collection.
One shows the insides with a DIP cable plugged in for the ROM.
That was an earlier attempt I made to "fix" the ROM instead of replacing
it. One shows the calc from the outside. That was the last photo I took.
Two show the circuit board that's mounted inside. I had intended for it
to sit right-side-up as shown in the one photo, but that's right where the
cover switches are, so it couldn't stay there. I had to flip it over and mount
it more in the center to clear the switches.
Bob's URL is http://www.tauntek.com/