jango2 wrote:
The video head's drum motor assembly has a magnetic cover that is
secured on with 2 or 3 screws (usualy non magnetic metal). On its rim
you'll see 1 or 2 black dots which are tiny magnets glued on to
generate a "pg" pulse. This pulse reports phase of drum rotation and
tells the head preamp when to read the video heads and when to switch
off in one rotation. A pg sensor is situated close to the lower drum
assembly to pick up these pulses.
1) Have you removed this part while cleaning and reinstalled it
incorrectly?.
2) I've had a case or 2 where the magnets were worn down and they
wouldn't generate enough of a pulse.
3) I've had cases where the allignment of lower drum with respect to
upper drum was out. An allen key locks the drum position to the shaft.
Has this loosened? Can the upper drum be shifted (with a bit of force)
while holding the lower drum tight?.
4) Bad pg sensor or a fault somewhere down the pg processing line.
5) Bad rotary transformer. The upper drum assy has a rotary
transformer primary winding housed in a ferrite base. This couples
the video signal to a similar secondary winding which is stationary.
I've seen breaks in these windings, and have rewound them to some
degree of usability. Jango

I've seen a shorted cap on the main board take out the PB 9v line...

Mark Z.