A W Sperry 620C oscilloscope vertical issue

[Keg]

I  recently  purchased  an  A  W  Sperry  620C  oscilloscope .  The  same  as  a  Hung  Chang .   I  purchased  it  as  working  and  found  there  was  a  problem  with  the  vertical  position .
When  you  have  the  vertical  position  knobs  fully  counter  clockwise ,  the  trace  is  still  above  the  center  of  the  screen .  When  you  turn  them  clockwise  the  trace  goes  up  and  off  the  screen .  This  happens  with  both  channels  so  it  must  be  after  the  vertical  amps .   I  worry  that  it  might  be  the  crt .   Help  please .
Thanks  KennyG 

[amspire]

The problem is not the tube.

There was a thread about this family of scope along with a manual.
https://www.eevblog.com/forum/testgear/my-$50-scope-seems-doa-tenma-72-720/msg271512/#msg271512

There are a number of different scopes with different front panels that seem to be the same inside.

If you are lucky, it will be a simple adjustment of VR6 as described in the manual.