I disassembled the head assembly and found that the coils were loose
and slightly lifted in the ferrite tracks of the rotary transformer. I
have heard that this is common on these old Fishers.
I performed the repair using super glue. I tried to get small wooden
wedges in to hold the coils down but could not seem to get them to
stay, so I did one section at a time, holding the coil down with a tiny
stick each time until the glue set. It was very arduous but I did get
it all glued down. Some glue did get on the faces of the ferrite disks
but I wiped it all off. The coils seemed to be laying flat in the
grooves after the procedure however they are not exactly concentric. By
this I mean that the grooves are a slightly larger diameter than the
coils. Therefore the coils are not exactly in the middle of the grooves
in every quadrant if you can picture this. I don't know if they ever
were or even if this very slight discrepancy is of any concern. I had
marked everything and I was very careful to reassemble it all as it was
taken apart. The procedure made no difference at all. The symptoms are
the same. I put the other set of heads back on but that made no
difference either. I still have continuity on both coils but I wonder
if I blundered the procedure somehow. Lenny

Mark D. Zacharias wrote:
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.