TDS684A Display problem

[mwbarth36]

I recently purchased a TDS684A scope with a problem in that the display will not adjust to the full width of the screen.  When originally purchased, both the vertical and Horizontal were compressed, although the horizontal much more than the vertical.  See the first attachment.  I was able to get the vertical back at the proper scale using the vertical size control, although now it is at the extreme end of it's range.  The thing I find strange is the display is focused, has sufficient brightness, and the linearity is good, it is simply compressed in the horizontal direction.  I have checked the 21 Volt supply generated on the video driver board and it is a solid 21 Volts. 

One of the reasons I like working on the TDS series of scopes is that one can operate the scope and have access to all circuits on the A10 and A11 boards, making service of these boards relatively easy.  Not so with the video boards!  They are not possible to access when the scope is assembled.  I suspect the problem would not be difficult to identify if one could scope the signals in the horizontal circuitry, but there is not hope of doing that.  I thought maybe someone has had this problem with a scope in the TDS series and could provide some insight into what the bad component is likely to be. 

Any suggestions or comments will be greatly appreciated!

[mwbarth36]

Anybody with a clue??  Thought sure I would find someone with this problem.

[james_s]

If the vertical adjustment is all the way to the extreme then obviously the vertical axis is not fixed either, you are compensating for a fault. Is it possible that the EHT is too high? The picture actually shrinks as the voltage gets higher.