Is it just a simple swap of the tack reader involved when one goes bad? other than having the proper replacement one. or is there more to it than just swaping out the bad one?
I belive I have a bad one in my ps2 5volt mikado. due to the engine just taking off like a rocket as soon as the throttle is set at speed step one. all other functions are working as normal.
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Yes, getting the right one with spacer under reader and soldering the 3 wires on it. But it could be the orange tach wire in harness is bad. Or the PCB at back of engine with cracked solder joint. Also do not count out dirty tach tape or flywheel or poor spacing. G
Of course, it could also be the circuitry on the PS/2 board set. 
However, I think the wiring and tether as George says is the first place to check.
His is a PS-2 5V, I do not think I have had one of those with a failed Speed control amp, ever. Go figure. G
Is there any way to test a tach reader, to see if it's bad, before going through the trouble of replacing it?
Try checking continuity on each wire with a meter, from the tach reader to where each wire attaches to the board at connector. Do this without powering up the engine. I have found bad wires in the past.
GGG posted:His is a PS-2 5V, I do not think I have had one of those with a failed Speed control amp, ever. Go figure. G
Come to think of it, I don't recall one on a 5V board either. Too bad they didn't use the same circuit for the 3V board! 
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