Hi
>
>have a HP1120 which is about 21" size ..(very nice tube..although has
>slight burn marks on it)
>
>anyway FAULT ...too much screen backgrond brightness ... almost can see
>the retrace lines ..all video signals there ..but on a whiteish
>background .. I thought there be just the normal screen pot @ the bottom
>of the FBT to adjust it ..but none ..the two pots are only for H & V
>focus .. in the end I just put about 3M ohm resistor between the ground
>and the HT to the tube grid board(board on back of the tube ..the HT
>thick red wire)..that brought it down ..but still have to run it with
>brightness adjustment almost to zero and even some of the contrast reduced
>
>Obviously something has failed ..with no circuits hard to tell..has
>anyone had similar experince with this model ..it is probably an open
>resistor in the screen grid circuit..
>
>help appreciated
every time I have seen this in monitors and TV its open circuit or high value resistors in the screen circuit (usually on neck board) as these R values are typically very very high - they are prone to failure
I would trace the wire back to the source of supply and inspect it for problems.
on one occasion where the screen voltage failed within the EHT transformer assembly and couldnt be accessed, I managed to take the voltage from the collector of the horizontal output transistor and feed it into the screen via a pot and resistors as a substitute source
it worked well.