Re: 468 DSO B timebase triggering
It seems that I may have not described what I called "intensity cycling"
very well. It is rather like a signal being applied to the Z-axis which is
close in frequency to that applied to the Y-axis, but not identical. The
brightness (or should I say the blanking) is "rolling" along the last full
waveform cycle under the conditions that I mentioned. The other feature
(which I think David has described as being "normal") is that the horizontal
trace doesn't extend over the last two divisions of the screen when the A
and B time-bases are set to the same rate. The waveform doesn't matter -
square, sine and triangle all show the same behaviour.
I appreciate that this isn't a display situation which one might normally
seek to use. It all came about from me checking out the triggering for both
time-bases. I understand how the B time-base can be used as a delayed
time-base but I don't feel insulted by Tom's suggestion that I am unfamiliar
I don't possess a 465B, though I do have the manual. I have to say that I am
surprised that there is similarity between the 468 and 465B scopes.
Superficially, most of the 400-series look similar, but the 464 and 466,
while looking very much alike, don't even share a CRT (I have 464, 468, 475A
and two non-functioning 466s from this series). The nature of the switching
of the 468, being a DSO, also has some obvious physical differences, largely
due to the digital logic, which I don't understand much at all!
From: TekScopes@... [mailto:TekScopes@...]
Sent: 20 January 2017 17:10
Subject: Re: [TekScopes] 468 DSO B timebase triggering
On Fri, 20 Jan 2017 16:33:04 -0000, you wrote:
Hi,Exactly. The levels do not need to be matched but if they are roughly
close, it makes things easier.
...The shortening of the B sweep when both timebases are set to the same
time/div is normal. It is caused by the B sweep being reset when the
A sweep completes. It also happens when the B sweep is slightly
faster than the A sweep and the delay time is high enough.
I can create the situation you describe on my 2232 if I adjust the B
trigger level to the very top or bottom of the waveform so that it
sometimes triggers on different cycles. *This makes me suspect that
any problem is with the B trigger itself.*
Is there any adjustment of the B trigger level which produces a stable
One thing which occurs to me is that if the B trigger input circuits
have a problem, then the fast edge of a square wave can make it
through but triggering performance will be poor. If so, testing with
a sine or triangle wave should make the problem worse.
The service manual has a test using sine waves for verifying the
performance of the A and B triggers separately.
I do not know what the access is like but just measuring the waveform
at the output of the B trigger input buffer will reveal if it is
operating correctly up to that point.
I have to say that, apart from this being a complex piece of kit, themanual
can be confusing, to say the least, in places. Page 4-49 is the beginningof
the "Triggering" section and refers to adjustment locations 2 and 3, butThe 468 is basically a 465B with the added DSO hardware so it might be
worth studying the 465B manual for additional operating instructions.
There is also a lot of similarity with the 465, 475, and 475A.
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