Repair – Arriflex Camera, Model S, Motor Speed Problem.
Arriflex motor for the S camera which uses a large power transistor on the side of the motor.
Complaint: motor would race in speed.
Repair: The motor must float electronically and therefore can not touch the case. There are four screws holding the transistor in its holder assembly. Make sure that each of the screws are not touching the transistor body. I had to place a very short piece of spaghetti along the screw shaft where it might come into contact with the transistor. I used only two spaghetti pieces on to the screws that actually reach the camera body. The other two screws only reach the base plate and can therefore touch the transistor.
Please understand that the mounting block for the transistor is composed of three plates. There is a large non conductive block on which the transistor rests. Over that transistor is a metal, conductive plate. The top plate is non conductive.
A real quick fix is to loosen the four screws and center the transistor so the two screw mounting holes that might touch the mounting screws will not touch. Loosen just enough so you can take a small tool and tap the transistor in proper place. Then tighten the four screws down snug. An ohm meter can be used to read from the screw to the transistor body. You should not read below 4ohms on the two screws that reach the main motor housing. The two screws that do not reach the main motor housing will read as a direct short which is normal.