1. TekScopes@groups.io

Re: 7T11 horizontal memory

Albert Otten
 

Hi Chris,

I might have good news for you.
The real time multivibrator doesn't work when you don't have a 7S11 adjacent to (or otherwise connected to) the 7T11. So then the memory gate is always blocked and you have no sweep output at the front panel.
You mean U512 I suppose. In real time ranges the horizontal amplifier now has one continuous ramp as input during the whole sweep of the 7T11. It depends on the time/div setting which outputs of U512 are really used in the amplifier chain. Not used outputs can be overdriven within short time without any consequence, and stay at some very high maximum level during the rest of the sweep . It's what I see happening.
I didn't pay attention to this in my previous post about equivalent time sampling but you essentially have the same situation then.

Albert

On Wed, Dec 5, 2018 at 03:23 PM, cmjones01 wrote:


I have now replaced the faulty R541 and R542. I also found that U572B, a Tek
special op-amp, was dead, I think due to a careless slip of my scope probe.
For now I've kludged a 741 in its place. Joy of joys, I have a horizontal
sweep in equivalent-time mode! Still blanked in real-time mode. I think
there's still something not right about the horizontal memory, which seems to
only be used in real-time mode (or am I wrong?). Anyhow, when I select a
real-time-mode sweep range, the output of U572B wanders up to about +12V and
stays there. I do have real-time sweep on the way in to the horizontal memory,
though. Will investigate further.

Chris

On Wed, Dec 5, 2018 at 06:07 AM, Albert Otten wrote:
One more suggestion. Set the 7T11 for MANUAL scan. Set the test scope at 5
or
10 us/div, trigger from the 7T11 pulse output. Then probe all TPs 512, 515,
525, 555 of the horizontal amplifier. In each period you will see one
horizontal line at a level determined by the SCAN knob setting. The level
increases from ground to some maximum when you rotate SCAN from left (ccw)
to
right (cw). The amounts and ratios depend on the setting of the 7T11
time/div
within its range. At TP555 the maximum should always be 5 V.
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