Nicely documented!
The only thing I can think of at the moment is to question the timing of the opening and closing of contacts when the Position Select Relay (K1) operates. During the transition is the common terminal completely open to both connections for a short interval or possibly connected to both simultaneously (unlikely)?
If both contacts are open briefly and the stored energy has not dissipated in the arc at the contact by the time the other contact closes, a spike could occur.
Can you check the contacts with an oscilloscope to see if some transients are getting through?
The Position Select and Coil Select switches are drawn as center open (3-position) switches. It does not matter for the Position Select since only one position controls K1. If the Coil Select switch is really a 3-position switch, try setting the selection to the center (No Coil Selected) position before switching K1. Since the coil grounds are switched by the Coil Select Relays, de-energizing BOTH relays before switching K1 should eliminate the possiblity of a transient when K1 switches. If S2 is not a 3-position switch, just disconnect its common from +15 V before switching K1 as a test.
Lynn
