1973 MBO launched the model 800, a simple pocket calculator with four
basic calculations. The unusual part of this calculator was, that it contained
apart from the flourescent display tube two additional LEDs for indicating negative
values and errors. At that time, LEDs were not as usual as today, which can you see
on the style of the LEDs.
|back side with open battery compartement|
Case and Keyboard
The case of the MBO 800 is of a rather modest quality: The hard and thin plastic
looks quite well, especially on the parts, where the white leather imitate is glued
upon, but it ages and tends to break on used edges.
The case is not of a small size, but that was pretty usual for a calculator made in 1973.
The battery compartement is styled a bit unusual, as you can see: The polarity markings
are made as conductor lines on the PCB. This is a clever way to avoid losing stickers
indicating the correct polarits.
Display and LEDs are beyond a large blackened plastic pane and allow a good readability even
in bright surroundings. The pane in front of the display is angeled a bit and the position
of the digits is marked upon.
In contrast to that, the keyboard is a very poorly made device: The keys have to feeling
at all the bounce terribly so that it is almost impossible to enter the desired numbers.
Worse to that, the mains switch has got massive contact problems.
While other keyboards can be opened and cleaned, this keyboard here is sealed and impossible
The problem with this keyboard not only appears on this very device, but also struggled me
twenty years ago on an other specimen of the MBO 800.
The MBO 800 resembles from its construction with the large mainboard, which fills more
than half of the case and the round VFD the state of the art of 1973, but there are still
a few details, which make it different from other calculators:
The PCB has got detailed printings, even with the name of the ICs, looks manually
populated and the calculator has got two large ICs looking almost identical.
|details of the mainboard|
A further noteworthy detail can be found on the connectors of the keyboard: Every
single key has got an own line; normally you would have a matrix here, reducing
the need for so many line. On the MBO 800 you have got 23 wires (including the
power switch) which connect the keyboard with the mainboard, and this might also
explain the sum of eighty(!) pins on the two large ICs.
in 1973 it was still usual for a pocket calculator to have a round VFD. Those
tubes had got a vacuum seal on the one side and lots of connector wires on the
other side. The MBO 800 uses exactly that kind of display tube, of the type
ISE DP 81A1, which is of course not very suitable for automatic assembly.
|two really vintage LEDs|
The display has got exactly eight digits and is because of this not capable to
show additional information like errors or negative numbers. For this, two pretty
vintage looking LEDs are used. Unlinke the display, which can best seen from the
front, you have to look from above to see the light of the LEDs. A typical case
of "form follows function", but not very economical.
On the PCB, two ICs with fourty pins are soldered, an ER 1432B (week 18, 1973) and an
ER 1422B (week 17, 1973). Those two ICs are completely unknown to literature, so I have
no idea about the functions (e.g. display driver, keyboard driver, CPU) of each of them.
The manufacturer of these chips is unknown, too.
|two ICs: ER1422B and ER1432B|
The calculating capabilities of the MBO 800 are rather normal for a
calculator of 1973 and are quite limited. It is only able to do the four
standard calculations, but already works with the standard entry logics
using the "=" key. Quaintingly it has got a constants function which only
works for multiplication and division.
|displaying negative numbers|
A division by zero is properly indicated with an error and overflow in both
directions also shows an error. On the multiplication, the overflow error is
not indicated, unless sixteen (twice the range of the display) digits
are exceeded. This can be fatal in your daily work!
|displaying an overflow error|
The displaying of regular numbers on the division is a bit buggy, as the
displays always shows the full eight digits, including the last zeros on the
right side of the comma. So, the simple division 1 / 2 is shown on
the display with the result of 0.5000000. A multiplication with
zeros after the comma results in adding more zeros on the right:
2.0 x 2.0 = results in 4.00, and because of the constants
function after the next "=" in 8.000, then 16.0000 and so on.
|displaying error on division by zero|
The MBO was, when it was launched in 1973, a pretty average calculator, which was
neither famous for its calculating capabilities nor for its contstruction and of course
not for its keyboard. But because of this, the price was probably rather low.
The specialities of this calculator are its display with VFD and LEDs and the
calculating logics, which does not show (besides on overflow of the multiplication)
wrong results, but as got some minor bugs, especially with zeros after the comma.
All this make the MBO 800 collecting worthy, and for me, this calculator was the
first one, I came into contact when I was six years old. My grandfather, who
bought it a few years ago, when he was already 78 years old, gave it to me, when
he got himself (at an age of over 80 years) a Privileg MD 585.
|calculator with original leather case|
|Display||8 digit VFD|
|Number of keys ||18|
|Functions||+ - * /|
|Entry logic (classification) ||ALG (BBD)|
|1 + 0.000 = ||1.000 (the correct value would be 1.)|
|0 / 0 = ||Error |
|Power supply ||4xAA|
|Size||14,4 x 8,7 x 2,7 cm|