Tek 2465B ch1, ch2 position/ clipping problem

[hb_miguel]

Hi all,

I am new so please forgive any repeats of past threads. I have a 2465B that I've been adjusting / testing but I can't figure out why channels
1 & 2 position voltage out of the channel multiplexer (U400) isn't up to spec.  All of the power supply voltages are good, the positioning inputs
to U100 and U200 pin 17 are close to spec (-4.5 - -5.16) but the output of U400 is +0.190 -> -0.104 when testing channels 1 & 2 (s/b +/- 0.7).
Channels 3 & 4 are where they should be @ +/- 0.35. The position display for ch1 & 2 stops at 3 grids up / 2 down from center (where +/- 4 is full range).
When at the extremes the on screen data displays jitter; channels 3 & 4 are fine. I'm hoping its something other than U400. Any guesses???

Thanks in advance

[bullet308]

http://tech.groups.yahoo.com/group/TekScopes/

Very tough to beat for these sorts of questions.