help repair of 21" hp monitor too much screen brightness

[mc]

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

 

[KLR]

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.

 

[mc]

well I sort of guessed that did check all the resistors on the neck
board there was only few and all ok a 2.2Mohm ad a 220kohm ..the ht
lead runs back to the centre of the driver board (I assume) ..due to
accesability I did not pull that out other than trying the resistor to
the ground on the ht lead on the neck board..which worked out to be
around 3.2Mohm ..it dulled the background ..well I will have to leave it
like this ..I just thought someone might have had a similar experince
and solved the problem.. If I had a circuit it be better to fault find it.

TNX for your suggestions