Electronics > Repair
Facit 1132 Nixie Calculator restoration
agent_power:
Hi community
I've got a Facit 1132 desktop calculator that I'm currently afraid to turn on. I've got no experience with tech of this vintage and I don't want to be the one that blows it up (it's unknown if the previous owner plugged it in).
Does the variac / dim bulb treatment apply here?
Anyone have service documentation for these or any other tips?
Attached are some pictures
Thanks
pqass:
The only technical info I found looking up the NEC ICs is this: https://dopecc.net/calculators/burroughs/c3317/tech/
There is a lot in common (power supply, ICs) with this model from Burroughs OEM'd by Sharp (from parent page), although the keyboard is different.
My first instincts is to test the power supply first since the ICs are unobtainium. The transistors on the other hand, if necessary, can likely be substituted with modern general purpose, power, and high-voltage NPN and PNP types (like MPS42, MPS92).
Fortunately, it looks like you can separate the logic and display PCBs by removing the screws either side of the blue keyboard connector and pulling it off. Then opening the black PCB ejectors (pulling on the black metal wedges toward you) and sliding out the PCBs. Also, you will likely need to remove the screws on top of the metal nixie bracket to release the display PCB.
The PS looks like a standard linear and doesn't look too complicated. Will likely need to reverse-engineer it to determine ground and the [looks to be at least four] output voltages it produces (based on number of TO-3s). MOST IMPORTANTLY, it will produce at least one 170V high-voltage output! And notice the two 450V blue caps. This is LETHAL! Find the wires that go to the edge connectors for the logic and display boards hidden below the PS PCB and short them to ground with a resistor (1K or so) and/or check with multimeter before touching (after having energized it).
Check fuses if they are still okay and capacitors for bulges or leaks (they look fine to me) before powering-up with a variac or at least dim-bulb. Measure the outputs for DC and AC (ripple). The problem here is that you don't know what voltages to expect if it isn't written on the PCBs. The most I could find is "...Japanese MOS IC NEC uPD105C. Logic states are 0 and -24V" (https://groups.google.com/g/oldcalculatorforum/c/GOUukTKy2tI). And I couldn't find any datasheet to help identify the power pins to work back to the PS. In reverse-engineering the PS, maybe you can identify zeners that can confirm the exact voltages. You can load down the outputs with resistors to determine if the voltages sag (say a few mA to 100mA). If there is low ripple (<50mV) and no voltage sag, you could try your luck and power up. But don't forget to bleed the PS outputs to zero before putting the logic and display PCBs back in.
EDIT:
Found this http://madrona.ca/e/eec/calctd/Casio121B_MMNotes.html link on a Casio calculator of that era that uses similar NEC ICs. Note the power supply outputs; -24V, +180V, +90V(?). This may be what you can expect in yours. Also some info on how it works. Similarly, this link https://www.oldcalculatormuseum.com/comp241.html although it may be less relevant.
Haenk:
I'd suggest testing the large caps before switching it on. 50+ years is a rather long time, and it probably has not been switched on for 50 years. That's just to make sure there is no noisy voltage which might or might not kill your chips.
However these japanese calculators are built like a tank and use only quality components. I bet it just works.
HarryDoPECC:
I play with quite a lot of these things and you have a combination with special risk:
- early generation ICs with low over-volt tolerance
- unobtanium ICs
- series pass regulator transistors that can fail short
In this situation at a minimum I recommend that you
- remove the boards (careful with ESD if there is any early MOS in there, I cannot recall just now)
- test that power supply with a reasonable dummy load.
Myself, after seeing an early Victor with 10% of its ICs actually exploded and blown apart after a series pass short -> overvoltage, I install simple fuse-zener-power transistor volt clamps on vulnerable supply rails. That transistor might be OK today, but tomorrow.....
Good luck, if you want further info then you could contact me via the dopecc.net site mentioned above. My site, it's nice to see that someone else has read it (!)
strawberry:
looks like brand new
looks like more modern couple chip calculators
dimm bulb wont protect unobtainable IC's
dimm bulb is for SMPS or high power expensive transistors you dont want to blow when you dont know 100% about control circuit functionality
carbon resistors may go open circuit or drifted out of spec.
it is possible to recreate IC's with modern components
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