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Calculators: Handheld: Serd Bonn
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| Size (actual): | 73.7mm
x 119.4mm x 28.3mm (max) (w,h,d) Weight 100g excluding batteries |
| Power: | 9.0V DC, 1 x PP3 size battery. It accepts an adapter (undefined) through a socket on the right in line with the on/off switch. |
| Case: | Two piece case in beige and and dark brown matt plastic which is gently wedged-shaped. Above the display area is a metallic plate with black text for the brand which sits in its own recess. A flush purple plastic display filter give a good easily viewable display. The small keys are soft and springy and work quite well. |
| Display: | 8 digit red LED with no ninth digit |
| Features: | Four standard functions with percentages |
| Age: | 1975/6 |
| Manufacturer: | Serd Deutschland (Germany), made in Japan, serial number 1120744S |
| Comments: | This German brand issued a number of calculators with the names of German cities. Sturdy enough calculator with simple functions. The logic is let down by seven digit negative numbers, a strange post division error and input overflow. |
| Components: |
1 x cpu: Mostek 50281N MT 7541 (week 41 of 1975), 28 pin DIL, 0.6" width black plastic 1 x IC: Toshiba T1347 5-D (April 1975), 20 pin DIL, 0.3" width black plastic 1 x nine LED module with integrated bubble lens (SL1892 B) 0 x transistors 0 x diodes 0 x capacitors 2 x resistors 1 x variable resistor |
| Boards: | On first opening you will see a metallic coated piece of cardboard protecting the main board, sitting loose and grounded. This is a bit odd as the case is plastic, so would not cause any electrical problems and you don't often see R.F. shielding in a calculator! The main board (Ref: 704 R-41X181 2 - (the two being a smaller number, so it looks like a version number)) sits face down on the keyboard assembly loosely supported by two plastic pillars. They are joined by two 11-way ribbon cables. The keyboard assembly if fixed to the front with four screws. |
| Construction: | Remove the single screw from the rear. This does not help a great deal as there are internal plastic lugs holding it together on the top and a tight fit on the other edges.. Start by pushing in the rear section on one side and travel around - careful, you may damage it. Eventually the back will lift off. When putting it back together start with the top edge. |
| Logic comments: | The (C) key on the first press can be used to clear the last entry whilst a second press clears the calculator completely, i.e. it is a C/CE key |
| Input overflow is not suppressed, keying in a ninth digit causes and error state which is recoverable using (C) - for a second register number | |
| Negative numbers are represented with a “-“ sign in the immediate left digit - but as there is no ninth digit you are limited to seven digit negative numbers | |
| There is automatic constant on all four functions - using the second register number | |
| Overflow shows the result flashing and is not recoverable using (C) | |
| Divide by zero shows a flashing zero which is not recoverable using (C) - if fact it gets very buggy: key in (5)(/)(0)(=)(C)(5)(=) to get "0" then (5)(=) to get "1" - so its has managed to transpose registers! | |
| The percentage key just divides the current register by 100 for one press only | |
| No other bugs found |
