I can't add much to this conversation, but remind me to never piss ZTatZAU off.
It sounds like there might be a deviation between the schematic diagram drawings and the as-built circuit boards.
It is something of a mystery as to why you are not showing three individual wire leads coming from the large wire coils that are exterior to the rotor housing.... assumed to be L-1 and L2. What are the yellow and white wires ...4 in all .... that appear in the very last of your photographs? ... I can't tell what they are connected to.
It may be that in a certain production era of electronic parts, the Q-13 transistor, an MJ2253, had a different case style.
It might be interesting to access the appropriate leads to the gyro circuit board .... one being the L-2 coil termination that goes to the switch, the other being the Q-13 emitter terminal .... that's the one with the arrow pointed inward ... and see if you could manually get the rotor to rotate a turn or two .... just by touching the negative capacitor terminal wire between these two points.
It looks like you are right about the two 'grayed out coils' being a part of the output signal circuit. The small metal crossbar between the two small coils should be slightly movable, relative to the coils.
When the airframe turned or rotated ... as in banking left or right ....
a resultant gyroscopic force would deflect the two small springs which are attached to the rotor assembly tab .. and the metal crossbar end pieces would move proportionally within the two small coils.
The resulting output signal would be amplified and sent to an actuator motor...
maybe to move some sort of compensating airfoil surface used in a turn.
The 10k R-3 potentiometer would used to zero the signal.
Maybe the circuit board that you have ... and have a picture of ... is just not the same thing as the original schematic that you first posted.
I am curious about the metal can transistor in the center of the small board.
It would be interesting to confirm if is PNP or NPN .... it has hole cut in the board for its top ....
Another question, the gyro (coil) that the little green CB came from, had overheated so badly that the interior of the gyro housing had puffed up and expanded to the point of fully encapsulating the rotor and gimble; locking them both in place. Is there a single component failure on the new schematic that would have likely caused this much overheating?
The drive transistor. They tend to fail short, and the coil's only intended for intermittant duty.
That new schematic does not match up with that green board.
Check my post on the previous page - I have the drive transistor marked "driver". Not the phototransistor, they can handle very little current.
The new schematic is closer, still not the same - count the transistors.
I don't see any reversing going on, but there's a pulse generator that's triggered by that Darlington (Q1 and Q2).
The adjustable resistor controls the width of pulses going to the motor, looks more like a start circuit than a speed control. That's a 10 or 20 turn pot, by the way.
See if I got these diodes right, and if those components with the "?" are caps or not.
If that little board is driving that coil, it looks like it's an NPN collector drive, and I don't see anything in the circuit to reverse the polarity.
When Q5 turns off, sharply, the flow of current through L1 and Q5 is interrupted and you get a sort of 'water hammer' effect, except with electric current rather than water.
The resulting voltage pulse travels through R10, CR2, R5, and R7 to turn on Q1, and reverse the current flow, which goes through Q1. .... Can you get the value of R8?
...either from the board or page 2 of the parts list. .... Also, it looks like some of the reverse current pulse goes through CR1 and R3 .... It's not really an efficient design, but apparently they got it to work.
You probably need to adjust the R7 pot. so that Q1 turns on just as Q5 turns off.
It ought to work if you can adjust R7 ... When you turn the R7 screw, take note of how many turns or quarter turns one way, and then the other that you adjust ... so you can go back to the original position if necessary.
Duffy says that Q1 and Q2 are a Darlington pair, but I'm not so sure. If Q1 turns on, then Q2 would tend to turn off. ... And Q2 current goes to a different place than Q1 current.
I would replace the 6V bulb with a 12V DC version.... probably last longer.
Also, maybe replace Q5, the power transistor. If there is evidence of heat damage, it may be defective. ... I would check it with a transistor testor ....They used to be easy to find ... not too expensive.
I don't see any speed control ... just that Q1 threshold using R7.
The new circuit and layout are not exactly the same .... but maybe close enough.
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