Tec 2445 , Broken trace , looks like a noisey brightness control

[Graham]

I'm getting what could be described as the trace being Z modulated
by a
pulse genarator , round 1 mS / cm time base , low brightness level
the
trace looks to be a series of joined up dots , moving across the
dispay , 1 , 2 ,3 or 4 beams all show the same

speed the tb up and the display looks quite normal , the fault only
shows on slow tb speeds

I have repaced the a9 eht board , after loosing the eht, the
replacement board is working normally and sets up as defined in the
book .

The 'noisey' beam problem was showing before the a9 board failed and
is
still showing after the replacement has been fitted .. so i assume
its
nothing to do with the 'eht' side of thing's

and ideas ?

Tnx - Graham ..