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Delayed trigger jitter on 535A

cmjones01
 

Tek fans,

My much-loved 535A has been getting a lot of use over the last few
weeks. It lives in my home lab which is where I'm now working due to
the coronavirus situation. Generally it's been a delight to use but
there's one niggle I think I need to sort out.

When using 'A' delayed by 'B' horizontal display mode, the trace has
significant horizontal jitter. For example, yesterday I was viewing a
1kHz rectangular wave and using the delayed timebase to examine one
edge. With timebase A set to 0.5us/cm, the viewed edge jitters back
and forward about 1-2us. The fault isn't always there - trying the
same test with the calibrator output, it was steady for the first 10
minutes or so and then got jittery.

If I back off timebase 'A's stability control so that it's triggering
on the edge after the delay, the jitter disappears as expected, so
it's something to do with the delay.

Before I start digging in to find the fault, has anyone experienced
anything like this with a dual-timebase 500 series scope -
535/545/546/547/549? I guess they're all fairly similar apart from
perhaps the 547.

Thank you
Chris

nicmatfr
 

Hi Chris
I don't have any experience with dual time base scopes, but I've seen trigger jitter on my 531A a few years ago. The problem was due to ripple on the 500 V supply, because of a faulty capacitor. Maybe have a look at the second timebase's supply.

Nicolas
________________________________________
De : TekScopes@groups.io [TekScopes@groups.io] de la part de cmjones01 [chris@...]
Envoyé : mercredi 8 avril 2020 11:44
À : TekScopes@groups.io
Objet : [TekScopes] Delayed trigger jitter on 535A

Tek fans,

My much-loved 535A has been getting a lot of use over the last few
weeks. It lives in my home lab which is where I'm now working due to
the coronavirus situation. Generally it's been a delight to use but
there's one niggle I think I need to sort out.

When using 'A' delayed by 'B' horizontal display mode, the trace has
significant horizontal jitter. For example, yesterday I was viewing a
1kHz rectangular wave and using the delayed timebase to examine one
edge. With timebase A set to 0.5us/cm, the viewed edge jitters back
and forward about 1-2us. The fault isn't always there - trying the
same test with the calibrator output, it was steady for the first 10
minutes or so and then got jittery.

If I back off timebase 'A's stability control so that it's triggering
on the edge after the delay, the jitter disappears as expected, so
it's something to do with the delay.

Before I start digging in to find the fault, has anyone experienced
anything like this with a dual-timebase 500 series scope -
535/545/546/547/549? I guess they're all fairly similar apart from
perhaps the 547.

Thank you
Chris

Rajesh VS
 

Hey Chris,

Assuming the power supply, switches contacts/pots, etc are clean, I would
also suggest to quickly run through trigger A Cal procedure to confirm its
not a cal issue.
Beyond that,
a) check both time bases independently on the given position to confirm
they are stable.
b) change to delayed trigger mode and check the delayed trigger pulse in
the front panel output to see if its stable
c) if it is jittery - you may wanna check through the difference amplifier
(V424 plate), Delayed Trigger multi (V445 B plate) and to the final delay
trigger amplifier (V428B) plate.
d) if your delay trigger pulse is stable, you may wanna check around
lockout multi/Delayed trigger amp in Timebase A (V114, V125, and V133 and
associated circuitry) - This is where the stability control also lives.

As you are aware, reference waveforms/DC bias levels etc are all available
in the manual.

Thanks
Rajesh

On Wed, Apr 8, 2020 at 2:45 AM cmjones01 <chris@...> wrote:

Tek fans,

My much-loved 535A has been getting a lot of use over the last few
weeks. It lives in my home lab which is where I'm now working due to
the coronavirus situation. Generally it's been a delight to use but
there's one niggle I think I need to sort out.

When using 'A' delayed by 'B' horizontal display mode, the trace has
significant horizontal jitter. For example, yesterday I was viewing a
1kHz rectangular wave and using the delayed timebase to examine one
edge. With timebase A set to 0.5us/cm, the viewed edge jitters back
and forward about 1-2us. The fault isn't always there - trying the
same test with the calibrator output, it was steady for the first 10
minutes or so and then got jittery.

If I back off timebase 'A's stability control so that it's triggering
on the edge after the delay, the jitter disappears as expected, so
it's something to do with the delay.

Before I start digging in to find the fault, has anyone experienced
anything like this with a dual-timebase 500 series scope -
535/545/546/547/549? I guess they're all fairly similar apart from
perhaps the 547.

Thank you
Chris



--
/Rajesh

cmjones01
 

On Wed, Apr 8, 2020 at 11:02 PM Rajesh VS <rajeshvs@...> wrote:
Assuming the power supply, switches contacts/pots, etc are clean, I would
also suggest to quickly run through trigger A Cal procedure to confirm its
not a cal issue.
...
Rajesh and Nicolas, thank you for the responses. I've just discovered
that the problem may actually be a phantom one: the signal I was
measuring was derived from an Atmel XMega microcontroller running from
its internal 32MHz clock. It turns out that this internal clock has
shockingly awful jitter. If I clock the same chip running the same
code from an external crystal, the jitter completely disappears! The
535A was telling the truth all along, and it was the modern
electronics that was giving the trouble.

There remains the issue of why the calibrator looked jittery, which I
will look in to when I can.

Chris