Aristo M75

Serial number 317, 2LT14 0612 (molded on upper edge)
Accessories none
Condition Front excellent. Back cover pretty dirty. 
Only a few dots on the display come on when the power supply is connected
Repairs, Comments 14.11.2002 Tried to repair the unit. Removed the plastic back cover and then 4 screws underneath the paper. The metal shield then easily comes off. Unsoldered the connector wires to the batteries. Couldn't find anything by visual inspection. 
However, I noticed that there must be a contact problem somewhere: At one point I had the display working and could even execute a calculation. So in principle it is working! 
Note that a dot on right side of the display seems to indicate when the power supply is connected. It is lit regardless of the setting of the power switch.
29.1.2003 Fixed a contact problem at the power connector. But I was unable to repair the 0/1 switch. In the end I had to solder a wire so that the calculator is permanently on regardless of the 0/1 switch when the power supply is connected.
Note that the unit won't work with batteries any more.
Acquired 10.11.2002

Serial number F2L005 0914 (molded on upper edge)
Accessories Protective plastic cover

AC 220V power supply
Condition Excellent!
Repairs, Comments
Acquired 3.2.2004
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Type, Precision, Input mode Scientific, 8 BCD digits, no exponent, Algebraic
Programmable No
Memory 1 register, not permanent
Special features Unusual function M+x. Instructions printed on the back.
Display 9 digit 7-segment red LED
Original Pricing, Production Unknown, approx. 1974 (or 1979?), Dennert & Pape, Hamburg Germany
Batteries 3xAA or DC power supply, 4.5V - 6V, minus on center (!)
Dimensions Length 15cm, Width 6cm, Height 2cm
Links See Aristo M64.
Comment The interesting thing is that is supports scientific functions like ex or 10x but doesn't supply exponential notation!
Calculator forensics value 10.4382.
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