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TEK 7704A with dual sweep funky??

I have two 7B53As and one 7B92 sweep plugins.
In a 7704A, they all have similar problems.
There's no pretrigger leadtime, can't see the leading
edge of the waveform.
The trace unblanks about 4 nS after the edge. If I crank
up the intensity enough to see that 4nS, the rest blooms badly.
Twiddling the trigger level control moves moves the edges all
around during the first 150 nS or so. The sweep isn't even
monotonic in that first 150nS. The sweep actually reverses
in 16nS intervals creating a bright spot and severe distortion
if you move an edge through the region. Acts like there's some
serious ringing on the first part of the sweep ramp.
There's nothing in the cal procedure about compensating this
region. I haven't tried poking around inside on an extender
yet, but I expect the extender effects will mask what I'm
looking for at these speeds.

I've got three 7704As that all exhibit this problem.

A 7B80/7B85 combination in any of the mainframes works flawlessly.
I've got 20 nS of pretrigger visibility. No nonlinearity of the
sweep. No blanking issues.

So, is there a failure mode in the dual sweep plugins that can
be corrected? I've got three that behave similarly, but
it's hard to believe they could ship 'em this way.
Fixes? Mods? Suggestions?

Thanks, mike

I have two 7B53As and one 7B92 sweep plugins.
In a 7704A, they all have similar problems.
There's no pretrigger leadtime, can't see the leading
edge of the waveform.
The trace unblanks about 4 nS after the edge. The sweep isn't even
monotonic in that first 150nS. The sweep actually reverses
in 16nS intervals creating a bright spot and severe distortion
if you move an edge through the region.

I've just checked out my 7704A using a 7B92A - and it works just fine. None
of the effects that you describe.

Craig

I fixed the 7B53As. The board mounting screws on one of the
inner boards were loose. Tightned the screws and both
the 7B53As now behave themselves.

That didn't help the 7B92. I tweeked the HF compensation
for minimum effect. It's still not right, 20nS ramp looks like
a stairway, but at least the
sweep doesn't run backwards any more. This is gonna be impossible
to find by probing around with a scope. The effect is smaller
than the ambient ground noise. Extender just makes it much worse.

mike

I fixed the 7B53As. The board mounting screws on one of the
inner boards were loose. Tightned the screws and both
the 7B53As now behave themselves.

I had exactly that problem with my 7B85. One of the spacer pillars was
loose - and this particular one was necessary to ensure ground continuity
between the boards. Symptom was that the readout on the CRT display was
intermittent.

Craig

Using the 7B92 in a 7704 is akin to stuffing a Ferrari engine in a Chevy
pickup. Looks and runs nice, but ...

The 7B92 is more appropriate in the 7904.

73, Dick, W1KSZ

Using the 7B92 in a 7704 is akin to stuffing a Ferrari engine in a Chevy
pickup. Looks and runs nice, but ...

Whereas it is true that the 7B92A is good to 500ps/div and the 7704A is only
specced at 2ns/div, there is absolutely no reason that the combination
should not work just fine. I find the 7704A is still pretty darned good to
1ns/div.

And yes - I generally use the 7B92A in either my 7904 or 7834, but the
question was asked about whether it would work in the 7704A - and the answer
is yes it does.

Cheers

Craig

17/03/2004 12:16:58, "Craig Sawyers" <c.sawyers@tech-
enterprise.com> wrote:

I've just checked out my 7704A using a 7B92A - and it works

just fine. None

of the effects that you describe.

Behaves properly with a 7B92(non-A) in my 7704A, here, too.
Definftely something screwy going on. (out of interest, what's in the
4th slot, when the 7B92's in the 3rd?

(There's a 7D10 in mine, for what it's worth. 'Digital events delay',
which I was hoping might be useful for picking a given line out of a
PAL frame - but if it's able to do that, I'm too dim to drive it, and
have no manual :(

Steve

17/03/2004 22:47:49, "Richard W. Solomon"
<w1ksz@...> wrote:

Using the 7B92 in a 7704 is akin to stuffing a Ferrari engine in a

Chevy

pickup. Looks and runs nice, but ...

Ah, you've met my tastes in automotive design, then :)
Also, if eBay throws you 7B92s (or Ferrari engines), there's a
tendency to use them for everything.

The 7B92 is more appropriate in the 7904.

Nope. That's where the 7B92_A_ lives. (actually, it lives in my
R7103, but you get the point...)

The original question was "does this plugin work in that scope?" -
and the answer is a definite yes...

As a slight aside, is there any downside to using overspecced
plugins? (other than the temptation to wind them to the
(uncalibrated) endstops from time to time?) Do they have an
inherently shorter life / tendency to oscillate that the scope just
ignores / some other fatal flaw?

Steve

18/03/2004 02:23:53, "Richard W. Solomon"
<w1ksz@...> wrote:

Using a 7B92A in a 7103 ... tsk, tsk, tsk ...
My choice is the 7B10 or 7B15 (I have two 7104's)

Only one horizontal slot in an R7103 - definitely a drawback.
Anyway, I'm normally probe-limited well before 200pS/div gets
useful. Oh look, a slightly sloping line :)

Steve