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Tek 11302 behavior

A

Ancient_Hacker

Jan 1, 1970
0
I just got a Tek 11302 scope. It's in fine shape and most everything
seems to work well.

Except for one thing-- the main trace pulses and flashes a bit-- if
you adjust the sweep speed just right, you can see the beam is going
off for a few milliseconds every 20 msec or so, probably to go refresh
all the legends on the screen.

Now I suspect that is supposed to happen during the retrace time and
not be quite so noticeable.

Can anybody confirm whether this is normal or abnormal behavior?



Thanks,

A_H
 
A

Andreas Tekman

Jan 1, 1970
0
I just got a Tek 11302scope. It's in fine shape and most everything
seems to work well.

Except for one thing-- the main trace pulses and flashes a bit-- if
you adjust the sweep speed just right, you can see the beam is going
off for a few milliseconds every 20 msec or so, probably to go refresh
all the legends on the screen.

Now I suspect that is supposed to happen during the retrace time and
not be quite so noticeable.

Can anybody confirm whether this is normal or abnormal behavior?

Thanks,

A_H

Normal scope behaviour. It's due to the mikroprocessor and screen/
readout technique used during times these scope series was developed.

hth,
Andreas
 
J

Jim Yanik

Jan 1, 1970
0
Normal scope behaviour. It's due to the mikroprocessor and screen/
readout technique used during times these scope series was developed.

hth,
Andreas

I can't recall if that's the 11K model with the scope-type CRT instead of a
video raster-scan display. The 7000 series had to interrupt the trace to
display on-screen readouts,it did not have a raster-scan CRT display.There
was provision to turn off the readout for non-interrupted traces in the 7K
series.(no microprocessor in the 7K series,it was a discrete analog readout
display,lots of TEK-made ICs.)

IIRC,other 11K scopes had a raster-scan video display,and should not have
to interrupt the display to show on-screen readouts.

I have no real experience with the 11K series,just what I've observed on
the other tech's benches.
 
A

Ancient_Hacker

Jan 1, 1970
0
Okay I found the answer in the service manual.

The scope has a "refresh priority" circuit. If you're asking for
maximum trace performace, with no holdoff, the scope has no choice but
to interrupt the trace to refresh the text. If there's some spare
non-trace time, like you've dialed in some holdoff, then the text
refreshing gets done then.

You'd think the scope could figure out how much idle time it has after
the sweep and before the next expected trigger. As is things flicker
a bit more than optimum.
 
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