KI256 problems, replacement options, etc

If the old one is Mod 11 and the new one is Mod 11, probably no AP cal is needed. This is because Mod 11 has a buffer on the output so they should be more consistent. See here.

If the old one is not Mod 11, try it, it will probably be ok, and anyway the AP will integrate out the pitch/roll errors.

Do you have a working vacuum indicator?

Certainly there could be a problem with the vacuum but to have both that, and a defective indicator which is not showing it, would be surprising. I have a vacuum pump but it would be a big thing to ship to Ireland

OTOH it is possible somebody scammed you. IME a good % of used avionics does not work and the seller knew it. I bought a “unused” SG102 3 years ago and when I installed it it showed intermittent errors when turning fairly fast, and it turned out it has been back to Sandel several times for an “overhaul” which was evidently a factory test which always passed, on the bench, hey ho, hey ho. I did get an unused fluxgate with it though.

The motor on mine is a dirt cheap motor which is all over Ebay. Search for
single phase motor
They are nearly all chinese and incredibly cheap. They all run at ~1300rpm; it’s the most you can physically do with 50Hz Don’t get one any smaller than mine; the vac pump needs a lot of torque. Mine says 90W.

And a chucked out vac pump will do just fine.

The vac gauge comes from a car parts shop which sells gauges for tarted-up cars (alongside 500 watt sound systems and all the other stuff boys without girlfriends out in their cars ).

For amusement (no STCs):

• A King AP can work perfectly well from a Castleberry electric AI (which is basically an electric KI256) with some mods

• You could do the same with an SG102 AHRS; I happen to have a KI256 pitch and roll emulator on a bench at home which uses the SG102 high speed ARINC429 data stream. It was an interesting project; done on an STM ARM 32F417 at 168MHz and 99.9% of it is running wholly in hardware (using counters, timers, DMA → DACs) and the CPU does basically nothing apart from parsing the ARINC429 data. The LVDT emulation is done entirely in software at 50Hz update rate, using 128 samples per cycle (a 3rd order Sallen-Key lowpass filter gives you a perfect sinewave output). The reference signal (400Hz nominally; 500Hz in a KFC225 system) is used as the phase reference, to 0.5 degree accuracy, auto-tracking 300-600Hz, and the waveform of the reference is irrelevant. The pitch/roll data could come from any other “AHRS” product, e.g. one of the countless matchbox-sized modules which are found in the “cheapo” avionics for the homebuilt market. 1 man-week, maybe 2-3 to put it in a nice box

The Garmin GI275 is a fully certified replacement for the KI256 and STC’d on multiple aircraft so it can be done successfully without lots of external interface boxes. But as suggested, it does require a GPS input and has internal air data computation.

@wigglyamp is the GI275 vulnerable to loss of “airdata” (whatever that means)?