Re: 453 follow-up


On Mon, 4 Nov 2013 01:55:49 +0100, you wrote:

. . .

However, there are a couple of minor functional failings left that I'd like to address.

1. When switching between normal/inverted modes on CH2, the zero line needs to be about half a division above the middle reticule in order for inverting to not move the line. I can "fix" that by tweaking the CH2 calibration settings, but not while also having proper vertical calibration as per the manual. Since there is no calibration procedure for this element, I am guessing that it might be normal, but is it?
The 454 added an adjustment (R334 in the middle of schematic 4) for the vertical
amplifier balance which could fix this. Tektronix apparently used it to prevent
position shift in ADD mode but I think it is effectively the same thing. You
could add a similar adjustment and calibrate out the channel 2 inverting mode
trace shift if it bothers you.

The 465 added separate adjustments for vertical amplifier balance and channel 2
inverting balance.

The 465 specification for inverting balance is 2 divisions so your 1/2 division
is well within the specification for later oscilloscopes. Typically I see it
shift a minor division at most on non 45x series oscilloscopes and it is
somewhat temperature sensitive.

2. More importantly and annoyingly, when switching from A/A-with-B to B sweep, the horisontal position moves about 3.5 division to the left. This happens at all sweep speeds and settings. I have tried to follow the circuit description, but I am only a humble software guy, so no joy as yet. Any suggestions?
I would take a look at the sweep start adjustments starting on page 6-45 of the
service manual. Before I decided something was wrong though, I would do a
complete horizontal calibration.

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