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Calculators: Handheld: Texas Instruments TI-2550 III
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Size (approx): |
80mm
(max) x 147mm x 32mm (max) (w,h,d) |
| Power: | Undefined, but uses a fixed rechargeable battery pack in the battery compartment - one unit integrated into cover. Uses charger BP-3 which is plugged into a socket on the top side, far left. A note on the battery pack states: "Caution, only use charger with the battery pack in place". | ||
| Case: | Two piece matt black case with gold painted trim. Brushed aluminium keyboard surround is coloured matt gold with shiny gold features around most of the keys. Black text labels sit above each key. A neutral display filter sits flush with the case and is supplemented with a lower label: black printed on a gold base for the brand and model details. | ||
| Display: | 8 digit green VFD display | ||
| Features: | Basic four function with percentages, square root, squares, inverse, three function memory and change sign | ||
| Age: | 1977 | ||
| Manufacturer: | Texas Instruments, assembled in the USA. Serial No. 230557 | ||
| Comments: | Nice feeling classic Texas calculator. The battery compartment directly exposes the main circuit board - which causes a problem if the batteries leak onto the board! Keys have a positive clicking sound. |
| Components: | 1 x cpu: Texas Instruments
TMS1043NL ZA0352 BSP7710 (date code week 10 of 1977), 0.3" width 28
pin DIL black plastic 1 x 9 digit VFD display (flat-faced glass) unit 0 x transistors 2 x diodes 1 x capacitor 3 x resistors and on the display power circuit 3 x transistors 4 x diodes 4 x capacitors 2 x resistors 1 x transformer: 1014324 7725 Malaysia (date code week 25 of 1977) |
| Boards: | The keyboard assembly sits lose above the main cpu board (Assy 1013205, 1013204-2 C) and is attached by 10 strong, short wires on the right to this board. A large slab of black plastic also separates the two. The main board is secured to the rear of the case by plastic guides and has a mini board for the VFD power driver circuit (no id marks). |
| Construction: | Remove the four screws from the rear (the top two are very large) and the whole assembly easily separates. |
| Logic comments: | (CE) is used to clear the last number entered, (C) to clear the calculator and (CM) to clear the memory |
| the (RV) key is used to exchange the display with the previous result or entry, i.e. register exchange | |
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This scan left shows the main cpu board with the piggy-backed display driver board. It uses the minimum extra components to keep costs low. |  |
This photo to the left shows a closer view of the mini-board - and is also backlit so you can the reverse side of the PCB showing through. |
