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How does this 60's transistor calculator function?

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The Guru

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I'm glad to announce that I have just acquired a 60's nixie calculator!:D

However, as mentioned by the seller, the calculator only works occasionally (though I have yet to see it do any math, the lazy thing;)).
w-addo9958.jpg
It's the Addo X 9958, which, after some research, turned out to be the exact same calculator as the Facit 1125 and the Burroughs C3350, all manufactured mostly by Sharp (yes, really).
Makes me wonder if they went for different prices, haha.

Anyway, I received a manual, instructing me to first clear the X and Y registers using the C key, after which to clear the two memory registers I and II.
The manual states that each time the calculator is turned on, it is blocked until the C, CI and CII buttons have been pressed and that the indicator lights for the error detection, CI and CII are lit.

Furthermore it states the E indicator light turns on to indicate error and either the CI or CII indicator lights is on when information is stored in register I or II, respectively.

Also https://www.oldcalculatormuseum.com/bc3350.html states that the register lights light up when their respective register contains a number (NOT 0).
It also tells us that "The machine has two memory registers which are based on magnetic core memory (the memory registers retain their content when power is turned off).".

A quick read into magnetic core memory (Wikipedia) informs me that its content is not lost when power is turned off.
This would make sense considering the registers have to be reset when the calculator is turned on: it is to be expected that every time the calculator is used, information is fed into the registers, thus requiring these registers to be cleared with every restart in the case of non-volatile (information-retaining) memory.
I suppose this was done to avoid errors.

To get to the problem, though, I'll describe the situation:
When I turn the calculator on, a random set (of adjacent) tubes lights up, displaying zeroes, and a decimal point appears in the right-most tube. Also the E indicator light does NOT light up (I suppose that's because I've previously cleared the display and result (X and Y) registers, I suspect it only lights up if these registers contain data, which is to be expected since nobody turns a calculator on to clear the memory and turn it back on afterwards).
When only one set of adjacent tubes lights up, all the tubes to the left of the leftmost lit tube start flickering (random bits of the zero in the tube start lighting up and a sometimes it appears the lit part circles the zero before turning off again for approximately half a second).
However, when two sets of two adjacent tubes light up, the tubes on both sides of the pairs start to flicker (again, all zeroes, which makes sense considering the display register is empty (0)). The space between these sets seems to be the same. I've had the sets appear in multiple places and even a few times where the left-most pair was cut in half (The left-most digit of the pair was "outside" the display).
However, this time it seems the right and left halves of the zeroes alternate eachother.
On yet another occasion, a single tube lights up and the tubes appear less spastic.
And to come to the last version I've seen: a pair of adjacent tubes lights up along with a pair with the previously mentioned set distance to the first set, except in this case the leftmost set flickers, slightly brighter than the other flickering tubes, and only a few other tubes flicker.

The minus sign is randomly on and off as well when I turn the calculator on, and the indicator light in the division key (Yep, it tells you when you're dividing or multiplying, fancy eh?) is lit, ALWAYS.

Worth mentioning is that when sometimes tubes flicker, other times they may be part of the pairs>
And when the calculator is turned on, a barely visible zero seems to "run" over the display from right to left.
It suppose the display drivers aren't the problem.

I've opened the calculator up once so far and haven't noticed any faults, but haven't removed the top board to inspect the two boards below fully.
I will do so soon and post some pictures.

The keyboard works via reed switches, with a magnet on the key: a very interesting design.
I haven't yet dared to desolder the keyboard and do measurements, but the register clear switches make the soft, whizzing sound of a reed switch, just like the keys on my other calculator which is functioning perfectly.
All the wires seem in place and everything looks very solid.

Turning the knob for setting the decimal point doesn't make the decimal point on the first tube turn off, or another decimal point appear anywhere.


My conclusion from the previously mentioned facts, is that the problem must be in the memory or the connections to it.
I do not know much about this calculator though, and information on the internet is minimal.

Thus I turn to the forum.
Does anybody know what is/might be the problem?:confused:

Your help would be greatly appreciated and never forgotten as long as I'll own this calculator, and I intend to keep it for a very long time!

I also believe apologies for the large article are in place, I hope the photos I will post soon will make up for it.
 

unclejed613

Well-Known Member
Most Helpful Member
as with anything else that old, random stuff means you have electrolytic caps dried out, especially in the power supply and around the voltage regulator circuits. you might have a noisy zener in one of the regulators, but try the E-caps first. you will also have lots of them at various places, on the power rails on the logic boards too...
 

The Guru

New Member
as with anything else that old, random stuff means you have electrolytic caps dried out, especially in the power supply and around the voltage regulator circuits. you might have a noisy zener in one of the regulators, but try the E-caps first. you will also have lots of them at various places, on the power rails on the logic boards too...

Thank you!:D

Is there any way of telling if a capacitor is dried out besides desoldering it and measuring it?
There's some high-voltage caps in there and my power supply only goes to 15 V...
 
Last edited:

The Guru

New Member
Indeed, a capacitor in the power supply seems to be bulging and there's green gunk around the hole for the lead.
It's rated 330 MFD... a somewhat unfortunate use of caps lock?
 
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