Help AC synchronous motor controller repair

[sasounet]

Hi.

I am a mechanical engineer with some electronic knowledge.

I need help understanding the schematic of a broken simple controller for an AC synchronous motor used on a vintage camera. Here is what I know (I think):

The controller works on 120Vac, one phase.
The motor is a 3 phases 48V AC synchronous.
Driving the 3 phases motor from one phase AC is done using a capacitor in the circuitry… Not sure how this is done but this is not what I think is broken
The motor is activated by a series of relays.
Forward or reverse operation is selected using a switch.
The controller generate an 8volts DC signal. This signal is forwarded to the camera. When the camera switch is activated, it trigger the relays in the controller, starting the motor.
This 8v signal also driving a small torque motor on the camera

This setup was working well up to yesterday. But now it is completely dead. Usually, when the switch is triggered, you can ear the relays clicking before the motor actually starts. Now the relays do not trigger at all. This is why I think the problem lies in the 8v circuitry somewhere so maybe it is a simple problem. Obviously, I have checked the fuse.

But the schematic is difficult for me to understand in order to start debugging the setup. Please have a look at the schematic. Maybe it will be simple to understand to some of you!!

[m k]

S1-1 and S2-1 are minus.
S3-1 is plus, round-3 through Si also.

Round-1 must become plus before anything else happens.
Then minus is connected to round-2 through S2-11-12 and to S3-4 through S2-13-14.

[sasounet]

Thanks a lot M K,

I guess then that when the trigger is pressed, Round-1 becomes positive and start the whole process. I will probe what happens. Is it that positive voltage is supplied to the camera through round-3, the switch on the camera, when engaged, sent positive voltage back to the controller thru round-1 then relays are triggered closing the circuit by making round-2 negative ?

Do you know the role of capacitor Cv ? When the box was working, it looked like DC power was kept being sent to the camera (round 2 low ?) for about 1 sec after the switch on the camera is closed. 

François

[m k]

Is it that positive voltage is supplied to the camera through round-3, the switch on the camera, when engaged, sent positive voltage back to the controller thru round-1 then relays are triggered closing the circuit by making round-2 negative ?

Yes, but round-2-3 is a different and independent circuit compared to others.

Do you know the role of capacitor Cv ? When the box was working, it looked like DC power was kept being sent to the camera (round 2 low ?) for about 1 sec after the switch on the camera is closed. 

It can have a dual job.
First it is a reservoir capacitor for DC voltage and then a disconnect delay through S3-11-12 for maybe braking.
So 1 sec delay is rational.

Motor side is nasty.
Round-4 connects to Tr2-(6) through S2-7-8, that is pretty straight forward, so is round-5 connecting to S4 through S1.
But fully rectified positive side of Tr1-right goes also to S4, it's active only when S3 connects but S2 is disconnected, there round-4 is sort of grounded through S3-7-8 and S2-7-5.
Finally Wi1 and C connects to Tr2-0 through S1 and when NSi changes its polarity C delays Tr2 primary voltage and so Tr1 and Tr2 secondaries have different phases.

One must bow those oldtimers.
They did quite a bit with quite a few.