Re: 2445 “A” sweep Issue


Siggi
 

Hey Chris,

it'd be mighty useful to see pictures of how your scope behaves, as I'm not
sure what "the start of the “A” sweep is off the CRT to the left" means. If
you input the calibrator signal to a channel and trigger on it, you should
be able to position the start of the sweep off the right and left edges of
the CRT as I recall. Does the horizontal position control work?
If you enable both A and B sweeps, do they start at roughly the same point
on the CRT?

Also note that the calibrator has a fairly precise frequency that adjusts
with the sweep speed you select to maintain 5 cycles of the square wave on
the CRT (up to point). You can therefore use the calibrator to assess
whether your sweeps are reasonably calibrated and whether they're linear.
Are they?
The 2445 is all drive by wire, where control voltages generated on the A5
board are used to set the sweep timing and the vertical gain of the scope.
The horizontal position control is one of those control signals, though it
should apply to both sweeps equally.
Sweep timing is also governed by control signals that are set through
calibration, so it's possible that some or all of your A sweep timings are
way off.

So far you're not giving us a whole lot of information to point you in
profitable direction though.

Siggi

On Thu, Sep 10, 2020 at 11:09 PM <christopherbath@hotmail.com> wrote:

Hi Siggi,

Thank you for your useful comments. The is a 2445 scope and not 2445A or
2445B.

I believe the scope has lost calibration data. The scope shows a failure
of Test 04. With a status of 11. Having a look at the service manual just
now I have found the following comment "If the bottom row of the readout
contains dots in the normally blank spaces, a wrong calibration constant
has been encountered. The instrument must be readjusted to remove the
incorrect calibration constant from the EAROM". This matches exactly with
what I am seeing on the CRT.

My suspicion is that the hybrid is working however I wanted to be sure as
the start of the “A” sweep is off the CRT to the left. I am assuming that
if the horizontal hybrid had failed then everything would have been to the
left.

The scope does seem to trigger. The Trigged LED illuminates when the Cal
signal is applied and trigger level adjusted.

Can the loss of the calibration constants result in the “A” sweep being
“lost”?

Thanks,

Chris







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