On 24 Feb 2016 15:53:50 -0800, you wrote:
This may be just a characteristic of the CRT. Tektronix sometimesI am not sure what you mean by voltage offset. With no sweep, there
specified a tolerance for geometric distortion inside and outside of
the center area. Toward the edges, you can usually find some geometry
error if you look closely enough.
According to the schematic for the horizontal amp, when the scope is set up in XY mode (as per the voltage measurement conditions) both plates should measure close to 52V. My 110V rail is 2V high, so it should measure 54V, but either way they should both be the same with the dot centered. Left plate measures 56.7V and Right plate measures 54.3V.It is normal for the CRT to have some vertical and horizontal offset
to produce a centered beam. To compensate for this, the CRT
amplifiers may have a centering adjustments. x1 horizontal centering
on the 468 is adjusted with R551 shown on schematic 10 and x10
horizontal centering is adjusted with R578 shown on schematic 10.
There are separate vertical centering adjustments for each input which
do the same thing.
The horizontal position control is off-center to the right side of the display by approx 2 divisions.This should be corrected by the procedure on page 4-64 if the
horizontal position control is already centered. Tektronix appears to
have left that out.
Their calibration procedure is pretty complicated and Tektronix doesAre you referring to the start point of the A and B sweeps not being
not say what the goal is unfortunately. I suspect some of the steps
could be done in a different order for better results.
I definitely want to fix this and get them aligned. I guess I'm a bit OCD...I sometimes trim the values of various parts or match transistors to
fix problems like these.
There is only one Sweep Start adjustment for both sweeps and based on
the design shown on schematic 8, there could be 100s of millivolts of
difference between the start points of the sweep generators do to the
matching of CR953/CR954 and CRsomething/CRsomething shown on schematic
8. Differential amplifier/comparators made up of Q958/Q960 and
Q987A/Q987B control the sweep start voltages. Oddly enough, the A
sweep uses a dual transistor which will have better matching while the
B sweep uses two separate transistors; I wonder why.
With an estimated CRT deflection of 1 volt per division at the sweep
output, a difference of 1 minor division or more is possible and your
first photograph shows an offset between the sweeps which is within
the design tolerances.
We have diagnosed other 465B type oscilloscopes here which had as much
offset between the sweeps.
If you want to trim the offset out, then I can make suggestion for how
to do it but it will require modifying the circuit slightly.
I just have a couple things to do and then I can get another picture or two uploaded, then do some waveform checking.