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7704A - Noise on sine-wave traces

 

When displaying a sine-wave where several cycles/division are present, when the READOUT is switched on, there is noticeable "noise" (for lack of a better definition) in the trace. It appears as tiny blank spots in the trace that move rapidly along the trace. The noise is not in sync with the triggering and appears at many points along the trace. Switching the readout off stops the effect.

The power supply has fresh filter caps as well as the horizontal board and the HV board so I don't think this is PS ripple and more likely digital noise from the READOUT circuitry but that's just a guess.

I've looked for places in the READOUT board and/or interface board where there might be bypass filtering components that might have been designed to eliminate this but I don't see anything. I do note that switching on the READOUT connects it to the +15V rail and possibly that's the source of the noise.

I've mostly observed this with sine-waves but it might be present with other waveforms. As a side note, with mostly square-waves, with the GRATICULE ILLUMINATION turned up, I can see a much smaller presentation of similar noise in the trace. This is much less noticeable but could be related.

Any ideas what I can look for as a cause for this?

Thanks,
Barry - N4BUQ
 

Correction: The READOUT switch connects to the -15V rail through R5006, not the +15V rail.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 9:14:41 AM
Subject: [TekScopes] 7704A - Noise on sine-wave traces
When displaying a sine-wave where several cycles/division are present, when the
READOUT is switched on, there is noticeable "noise" (for lack of a better
definition) in the trace. It appears as tiny blank spots in the trace that
move rapidly along the trace. The noise is not in sync with the triggering and
appears at many points along the trace. Switching the readout off stops the
effect.

The power supply has fresh filter caps as well as the horizontal board and the
HV board so I don't think this is PS ripple and more likely digital noise from
the READOUT circuitry but that's just a guess.

I've looked for places in the READOUT board and/or interface board where there
might be bypass filtering components that might have been designed to eliminate
this but I don't see anything. I do note that switching on the READOUT
connects it to the +15V rail and possibly that's the source of the noise.

I've mostly observed this with sine-waves but it might be present with other
waveforms. As a side note, with mostly square-waves, with the GRATICULE
ILLUMINATION turned up, I can see a much smaller presentation of similar noise
in the trace. This is much less noticeable but could be related.

Any ideas what I can look for as a cause for this?

Thanks,
Barry - N4BUQ
 

Do not do anything.

There is one beam.? It has to be "borrowed" to write the readouts.

There are two ways:

1) Borrow the beam when it's needed.? This chops tiny holes in the trace.? it's going to be obvious at some sweep speeds, but will work on slow sweeps.

2) refresh the readouts on the sweep retrace.? This eliminates the "noise" but for slow sweep speeds, you will get a flickering readout.

There's generally a switch on the readout board to control this behavior.

Harvey

On 12/30/2021 10:14 AM, n4buq wrote:
When displaying a sine-wave where several cycles/division are present, when the READOUT is switched on, there is noticeable "noise" (for lack of a better definition) in the trace. It appears as tiny blank spots in the trace that move rapidly along the trace. The noise is not in sync with the triggering and appears at many points along the trace. Switching the readout off stops the effect.

The power supply has fresh filter caps as well as the horizontal board and the HV board so I don't think this is PS ripple and more likely digital noise from the READOUT circuitry but that's just a guess.

I've looked for places in the READOUT board and/or interface board where there might be bypass filtering components that might have been designed to eliminate this but I don't see anything. I do note that switching on the READOUT connects it to the +15V rail and possibly that's the source of the noise.

I've mostly observed this with sine-waves but it might be present with other waveforms. As a side note, with mostly square-waves, with the GRATICULE ILLUMINATION turned up, I can see a much smaller presentation of similar noise in the trace. This is much less noticeable but could be related.

Any ideas what I can look for as a cause for this?

Thanks,
Barry - N4BUQ
 

Hi Harvey,

I'll see if that resolves the issue. The way that the blanks move along the trace, it seemed a more random effect than I'd expect when writing to the same locations each time but maybe not.

Thanks!
Barry - N4BUQ

----- Original Message -----
From: "Harvey White" <madyn@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 9:42:50 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Do not do anything.

There is one beam.? It has to be "borrowed" to write the readouts.

There are two ways:

1) Borrow the beam when it's needed.? This chops tiny holes in the
trace.? it's going to be obvious at some sweep speeds, but will work on
slow sweeps.

2) refresh the readouts on the sweep retrace.? This eliminates the
"noise" but for slow sweep speeds, you will get a flickering readout.

There's generally a switch on the readout board to control this behavior.

Harvey


On 12/30/2021 10:14 AM, n4buq wrote:
When displaying a sine-wave where several cycles/division are present, when the
READOUT is switched on, there is noticeable "noise" (for lack of a better
definition) in the trace. It appears as tiny blank spots in the trace that
move rapidly along the trace. The noise is not in sync with the triggering and
appears at many points along the trace. Switching the readout off stops the
effect.

The power supply has fresh filter caps as well as the horizontal board and the
HV board so I don't think this is PS ripple and more likely digital noise from
the READOUT circuitry but that's just a guess.

I've looked for places in the READOUT board and/or interface board where there
might be bypass filtering components that might have been designed to eliminate
this but I don't see anything. I do note that switching on the READOUT
connects it to the +15V rail and possibly that's the source of the noise.

I've mostly observed this with sine-waves but it might be present with other
waveforms. As a side note, with mostly square-waves, with the GRATICULE
ILLUMINATION turned up, I can see a much smaller presentation of similar noise
in the trace. This is much less noticeable but could be related.

Any ideas what I can look for as a cause for this?

Thanks,
Barry - N4BUQ
 

There's likely no relationship between the chopping frequency and the sweep speed.? I'd go for random.

You're thinking that this behaves like digital, perhaps?

Harvey

On 12/30/2021 10:46 AM, n4buq wrote:
Hi Harvey,

I'll see if that resolves the issue. The way that the blanks move along the trace, it seemed a more random effect than I'd expect when writing to the same locations each time but maybe not.

Thanks!
Barry - N4BUQ

----- Original Message -----
From: "Harvey White" <madyn@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 9:42:50 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Do not do anything.

There is one beam.? It has to be "borrowed" to write the readouts.

There are two ways:

1) Borrow the beam when it's needed.? This chops tiny holes in the
trace.? it's going to be obvious at some sweep speeds, but will work on
slow sweeps.

2) refresh the readouts on the sweep retrace.? This eliminates the
"noise" but for slow sweep speeds, you will get a flickering readout.

There's generally a switch on the readout board to control this behavior.

Harvey


On 12/30/2021 10:14 AM, n4buq wrote:
When displaying a sine-wave where several cycles/division are present, when the
READOUT is switched on, there is noticeable "noise" (for lack of a better
definition) in the trace. It appears as tiny blank spots in the trace that
move rapidly along the trace. The noise is not in sync with the triggering and
appears at many points along the trace. Switching the readout off stops the
effect.

The power supply has fresh filter caps as well as the horizontal board and the
HV board so I don't think this is PS ripple and more likely digital noise from
the READOUT circuitry but that's just a guess.

I've looked for places in the READOUT board and/or interface board where there
might be bypass filtering components that might have been designed to eliminate
this but I don't see anything. I do note that switching on the READOUT
connects it to the +15V rail and possibly that's the source of the noise.

I've mostly observed this with sine-waves but it might be present with other
waveforms. As a side note, with mostly square-waves, with the GRATICULE
ILLUMINATION turned up, I can see a much smaller presentation of similar noise
in the trace. This is much less noticeable but could be related.

Any ideas what I can look for as a cause for this?

Thanks,
Barry - N4BUQ
 

Yes - I was thinking it was digital noise coming from the readout character generation circuits.

I tried the switch in the GATED position and that does indeed eliminate [almost] all of the gaps in the trace. Oddly, there are still two or three gaps that stay in the same position along the trace. Furthermore, adjusting the HOLDOFF on the time-base moves the gaps along the trace in "steps". I'm not sure if that's normal but perhaps it is.

I like the readout in this mode. Yes, it gets odd with slow sweeps but when in FREE RUN, the readout characters bounce/wave under certain waveforms and input frequencies. I think someone (maybe that was you?) that told me there are past posts regarding how to fix that but I don't think I ever found that (or wasn't able to get it adjusted properly). In any case, in GATED, that's eliminated (albeit it becomes a bit of an issue having the time-base selected by the GATE SELECTOR switch).

While looking through the manual, I found that removing Q3416 causes the system to display full rows in the upper and lower rows allowing proper centering, etc., of the readout characters. Fun stuff.

Thanks again,
Barry - N4BUQ

----- Original Message -----
From: "Harvey White" <madyn@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 9:59:43 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
There's likely no relationship between the chopping frequency and the
sweep speed.? I'd go for random.

You're thinking that this behaves like digital, perhaps?

Harvey

On 12/30/2021 10:46 AM, n4buq wrote:
Hi Harvey,

I'll see if that resolves the issue. The way that the blanks move along the
trace, it seemed a more random effect than I'd expect when writing to the same
locations each time but maybe not.

Thanks!
Barry - N4BUQ

----- Original Message -----
From: "Harvey White" <madyn@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 9:42:50 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Do not do anything.

There is one beam.? It has to be "borrowed" to write the readouts.

There are two ways:

1) Borrow the beam when it's needed.? This chops tiny holes in the
trace.? it's going to be obvious at some sweep speeds, but will work on
slow sweeps.

2) refresh the readouts on the sweep retrace.? This eliminates the
"noise" but for slow sweep speeds, you will get a flickering readout.

There's generally a switch on the readout board to control this behavior.

Harvey


On 12/30/2021 10:14 AM, n4buq wrote:
When displaying a sine-wave where several cycles/division are present, when the
READOUT is switched on, there is noticeable "noise" (for lack of a better
definition) in the trace. It appears as tiny blank spots in the trace that
move rapidly along the trace. The noise is not in sync with the triggering and
appears at many points along the trace. Switching the readout off stops the
effect.

The power supply has fresh filter caps as well as the horizontal board and the
HV board so I don't think this is PS ripple and more likely digital noise from
the READOUT circuitry but that's just a guess.

I've looked for places in the READOUT board and/or interface board where there
might be bypass filtering components that might have been designed to eliminate
this but I don't see anything. I do note that switching on the READOUT
connects it to the +15V rail and possibly that's the source of the noise.

I've mostly observed this with sine-waves but it might be present with other
waveforms. As a side note, with mostly square-waves, with the GRATICULE
ILLUMINATION turned up, I can see a much smaller presentation of similar noise
in the trace. This is much less noticeable but could be related.

Any ideas what I can look for as a cause for this?

Thanks,
Barry - N4BUQ
 

Hi Barry, please reread message 187015. Albert
 

I remember now that this involves adjustment of the LF Compensation. The calibration steps for that calls for a standardizer fixture and I don't have one of those. Is there a way to make that adjustment without a standardizer fixture?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 12:16:56 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry, please reread message 187015. Albert
 

1) AKA Chop mode, 2) AKA Alt mode.? ?Both useful but at different sweep speeds.? ? ? Jim FordSent from my T-Mobile 4G LTE Device

-------- Original message --------From: Harvey White <madyn@...> Date: 12/30/21 7:46 AM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces Do not do anything.There is one beam.? It has to be "borrowed" to write the readouts.There are two ways:1) Borrow the beam when it's needed.? This chops tiny holes in the trace.? it's going to be obvious at some sweep speeds, but will work on slow sweeps.2) refresh the readouts on the sweep retrace.? This eliminates the "noise" but for slow sweep speeds, you will get a flickering readout.There's generally a switch on the readout board to control this behavior.HarveyOn 12/30/2021 10:14 AM, n4buq wrote:> When displaying a sine-wave where several cycles/division are present, when the READOUT is switched on, there is noticeable "noise" (for lack of a better definition) in the trace.? It appears as tiny blank spots in the trace that move rapidly along the trace.? The noise is not in sync with the triggering and appears at many points along the trace.? Switching the readout off stops the effect.>> The power supply has fresh filter caps as well as the horizontal board and the HV board so I don't think this is PS ripple and more likely digital noise from the READOUT circuitry but that's just a guess.>> I've looked for places in the READOUT board and/or interface board where there might be bypass filtering components that might have been designed to eliminate this but I don't see anything.? I do note that switching on the READOUT connects it to the +15V rail and possibly that's the source of the noise.>> I've mostly observed this with sine-waves but it might be present with other waveforms.? As a side note, with mostly square-waves, with the GRATICULE ILLUMINATION turned up, I can see a much smaller presentation of similar noise in the trace.? This is much less noticeable but could be related.>> Any ideas what I can look for as a cause for this?>> Thanks,> Barry - N4BUQ>>> >>>
 

It is indeed interesting to slow the sweep speed down to about 0.5s or more and watch the readout written after the sweep completes. I had not seen that before today.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Jim Ford" <james.ford@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 6:52:39 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
1) AKA Chop mode, 2) AKA Alt mode.? ?Both useful but at different sweep speeds.
? ? ? Jim FordSent from my T-Mobile 4G LTE Device
-------- Original message --------From: Harvey White <madyn@...>
Date: 12/30/21 7:46 AM (GMT-08:00) To: [email protected] Subject: Re:
[TekScopes] 7704A - Noise on sine-wave traces Do not do anything.There is one
beam.? It has to be "borrowed" to write the readouts.There are two ways:1)
Borrow the beam when it's needed.? This chops tiny holes in the trace.? it's
going to be obvious at some sweep speeds, but will work on slow sweeps.2)
refresh the readouts on the sweep retrace.? This eliminates the "noise" but for
slow sweep speeds, you will get a flickering readout.There's generally a switch
on the readout board to control this behavior.HarveyOn 12/30/2021 10:14 AM,
n4buq wrote:> When displaying a sine-wave where several cycles/division are
present, when the READOUT is switched on, there is noticeable "noise" (for lack
of a better definition) in the trace.? It appears as tiny blank spots in the
trace that move rapidly along the trace.? The noise is not in sync with the
triggering and appears at many points along the trace.? Switching the readout
off stops the effect.>> The power supply has fresh filter caps as well as the
horizontal board and the HV board so I don't think this is PS ripple and more
likely digital noise from the READOUT circuitry but that's just a guess.>> I've
looked for places in the READOUT board and/or interface board where there might
be bypass filtering components that might have been designed to eliminate this
but I don't see anything.? I do note that switching on the READOUT connects it
to the +15V rail and possibly that's the source of the noise.>> I've mostly
observed this with sine-waves but it might be present with other waveforms.? As
a side note, with mostly square-waves, with the GRATICULE ILLUMINATION turned
up, I can see a much smaller presentation of similar noise in the trace.? This
is much less noticeable but could be related.>> Any ideas what I can look for
as a cause for this?>> Thanks,> Barry - N4BUQ>>> >>>
 

I see where Table 4-1, Item 3 (Signal Standardizer Calibration Fixture) states that "Calibrated 7000-series plug-in units with suitable signal sources may be substituted if lower performance is acceptable." I just don't quite see where the instructions outline how to set those up in place of the standardizer - particularly for low-frequency linearity and/or vertical high-frequency compensation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 5:11:41 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
I remember now that this involves adjustment of the LF Compensation. The
calibration steps for that calls for a standardizer fixture and I don't have
one of those. Is there a way to make that adjustment without a standardizer
fixture?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 12:16:56 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry, please reread message 187015. Albert
 

I think that's where the "lower performance" comes in.

I think what you have to make the assumption of, is that the subject "standard" plugin is somehow correct and in calibration.

Using this as a reference makes all things equally wrong.

Harvey

On 12/30/2021 8:13 PM, n4buq wrote:
I see where Table 4-1, Item 3 (Signal Standardizer Calibration Fixture) states that "Calibrated 7000-series plug-in units with suitable signal sources may be substituted if lower performance is acceptable." I just don't quite see where the instructions outline how to set those up in place of the standardizer - particularly for low-frequency linearity and/or vertical high-frequency compensation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 5:11:41 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
I remember now that this involves adjustment of the LF Compensation. The
calibration steps for that calls for a standardizer fixture and I don't have
one of those. Is there a way to make that adjustment without a standardizer
fixture?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 12:16:56 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry, please reread message 187015. Albert
 

Hi Barry,

For minimizing that wavy readout forget about the signal standardizer. Display your signal (calibrator or whatever) at full height (8 div) and the time base for the most nervous readout. Then rotate R4465 (Vert. Amp.) for the best setting (most quiet readout).
Note that this setting is also best for your ordinary signal response. If the result is still unsatisfactory then perhaps a slight readjustment of R4453 might help (but remember the original setting, just in case).

Albert

On Fri, Dec 31, 2021 at 02:13 AM, n4buq wrote:


I see where Table 4-1, Item 3 (Signal Standardizer Calibration Fixture) states
that "Calibrated 7000-series plug-in units with suitable signal sources may be
substituted if lower performance is acceptable." I just don't quite see where
the instructions outline how to set those up in place of the standardizer -
particularly for low-frequency linearity and/or vertical high-frequency
compensation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 5:11:41 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
I remember now that this involves adjustment of the LF Compensation. The
calibration steps for that calls for a standardizer fixture and I don't have
one of those. Is there a way to make that adjustment without a standardizer
fixture?
 

I can confirm Albert's procedure, I have adjusted several scopes with the wavy readout issue as suggested,I think 7904 , 7104 and 7603 for this same issue.

No CAL or standardizer needed.

Jon
 

Hi Albert,

That works! I was just hesitant to start changing the settings without knowing more about what they affect. Very nice to have the wavy readouts stable.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 6:53:41 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry,

For minimizing that wavy readout forget about the signal standardizer. Display
your signal (calibrator or whatever) at full height (8 div) and the time base
for the most nervous readout. Then rotate R4465 (Vert. Amp.) for the best
setting (most quiet readout).
Note that this setting is also best for your ordinary signal response. If the
result is still unsatisfactory then perhaps a slight readjustment of R4453
might help (but remember the original setting, just in case).

Albert

On Fri, Dec 31, 2021 at 02:13 AM, n4buq wrote:


I see where Table 4-1, Item 3 (Signal Standardizer Calibration Fixture) states
that "Calibrated 7000-series plug-in units with suitable signal sources may be
substituted if lower performance is acceptable." I just don't quite see where
the instructions outline how to set those up in place of the standardizer -
particularly for low-frequency linearity and/or vertical high-frequency
compensation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 5:11:41 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
I remember now that this involves adjustment of the LF Compensation. The
calibration steps for that calls for a standardizer fixture and I don't have
one of those. Is there a way to make that adjustment without a standardizer
fixture?
 

Hi Barry , I have been watching these postings with interest . One of my 7844's has this or a remarkably similar problem . There is the wavy / jumping about readout but in my case it is made worse by using the position control -- did this happen with yours . I would be pleased to know how similar my case is and maybe if its not the same there might be suggestions of where the problem might be .
many thanks in advance for help from anyone reading this
Brian? (UK)

On Friday, 31 December 2021, 17:16:11 GMT, n4buq <n4buq@...> wrote:

Hi Albert,

That works!? I was just hesitant to start changing the settings without knowing more about what they affect.? Very nice to have the wavy readouts stable.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 6:53:41 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry,

For minimizing that wavy readout forget about the signal standardizer.? Display
your signal (calibrator or whatever) at full height (8 div) and the time base
for the most nervous readout. Then rotate R4465 (Vert. Amp.) for the best
setting (most quiet readout).
Note that this setting is also best for your ordinary signal response. If the
result is still unsatisfactory then perhaps a slight readjustment of R4453
might help (but remember the original setting, just in case).

Albert

On Fri, Dec 31, 2021 at 02:13 AM, n4buq wrote:


I see where Table 4-1, Item 3 (Signal Standardizer Calibration Fixture) states
that "Calibrated 7000-series plug-in units with suitable signal sources may be
substituted if lower performance is acceptable."? I just don't quite see where
the instructions outline how to set those up in place of the standardizer -
particularly for low-frequency linearity and/or vertical high-frequency
compensation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 5:11:41 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
I remember now that this involves adjustment of the LF Compensation.? The
calibration steps for that calls for a standardizer fixture and I don't have
one of those.? Is there a way to make that adjustment without a standardizer
fixture?
 

Hi Brian,

I presume you're referring to the vertical positioning control and not the horizontal positioning control but I presume the vertical one. I did not notice that made much, if any, difference. I don't fully understand this but I think the waviness is caused by overshoot/undershoot of the beam as it jumps from the trace to the readout. If that's the case, then I would think that different vertical positions of the trace would affect this.

Overall, I think I prefer the GATED setting (draws the readout after the traces); however, at least for the 7704A, there's a switch that selects which B slot drives the readout so one must choose one or the other and I'm pretty sure I'm going to forget that setting when I have just one time-base in the B position which will disable the readout. Maybe not but for now, I'm going to leave it in the GATED position.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Brian via groups.io" <brianas1948@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 11:26:08 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry , I have been watching these postings with interest . One of my 7844's
has this or a remarkably similar problem . There is the wavy / jumping about
readout but in my case it is made worse by using the position control -- did
this happen with yours . I would be pleased to know how similar my case is and
maybe if its not the same there might be suggestions of where the problem might
be .
many thanks in advance for help from anyone reading this
Brian? (UK)

On Friday, 31 December 2021, 17:16:11 GMT, n4buq <n4buq@...> wrote:

Hi Albert,

That works!? I was just hesitant to start changing the settings without knowing
more about what they affect.? Very nice to have the wavy readouts stable.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 6:53:41 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry,

For minimizing that wavy readout forget about the signal standardizer.? Display
your signal (calibrator or whatever) at full height (8 div) and the time base
for the most nervous readout. Then rotate R4465 (Vert. Amp.) for the best
setting (most quiet readout).
Note that this setting is also best for your ordinary signal response. If the
result is still unsatisfactory then perhaps a slight readjustment of R4453
might help (but remember the original setting, just in case).

Albert

On Fri, Dec 31, 2021 at 02:13 AM, n4buq wrote:


I see where Table 4-1, Item 3 (Signal Standardizer Calibration Fixture) states
that "Calibrated 7000-series plug-in units with suitable signal sources may be
substituted if lower performance is acceptable."? I just don't quite see where
the instructions outline how to set those up in place of the standardizer -
particularly for low-frequency linearity and/or vertical high-frequency
compensation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 5:11:41 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
I remember now that this involves adjustment of the LF Compensation.? The
calibration steps for that calls for a standardizer fixture and I don't have
one of those.? Is there a way to make that adjustment without a standardizer
fixture?
 

I think what I wrote is confusing. This is probably clearer:

Overall, I think I prefer the GATED setting (draws the readout after the traces); however, at least for the 7704A, there's a switch that selects which HORIZONTAL slot drives the readout so one must choose the A or the B slot and I'm pretty sure I'm going to forget that setting when I have just one time-base in the B position which will disable the readout. Maybe not but for now, I'm going to leave it in the GATED position.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 12:07:42 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Brian,

I presume you're referring to the vertical positioning control and not the
horizontal positioning control but I presume the vertical one. I did not
notice that made much, if any, difference. I don't fully understand this but I
think the waviness is caused by overshoot/undershoot of the beam as it jumps
from the trace to the readout. If that's the case, then I would think that
different vertical positions of the trace would affect this.

Overall, I think I prefer the GATED setting (draws the readout after the
traces); however, at least for the 7704A, there's a switch that selects which B
slot drives the readout so one must choose one or the other and I'm pretty sure
I'm going to forget that setting when I have just one time-base in the B
position which will disable the readout. Maybe not but for now, I'm going to
leave it in the GATED position.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Brian via groups.io" <brianas1948@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 11:26:08 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry , I have been watching these postings with interest . One of my 7844's
has this or a remarkably similar problem . There is the wavy / jumping about
readout but in my case it is made worse by using the position control -- did
this happen with yours . I would be pleased to know how similar my case is and
maybe if its not the same there might be suggestions of where the problem might
be .
many thanks in advance for help from anyone reading this
Brian? (UK)

On Friday, 31 December 2021, 17:16:11 GMT, n4buq <n4buq@...> wrote:

Hi Albert,

That works!? I was just hesitant to start changing the settings without knowing
more about what they affect.? Very nice to have the wavy readouts stable.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 6:53:41 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry,

For minimizing that wavy readout forget about the signal standardizer.? Display
your signal (calibrator or whatever) at full height (8 div) and the time base
for the most nervous readout. Then rotate R4465 (Vert. Amp.) for the best
setting (most quiet readout).
Note that this setting is also best for your ordinary signal response. If the
result is still unsatisfactory then perhaps a slight readjustment of R4453
might help (but remember the original setting, just in case).

Albert

On Fri, Dec 31, 2021 at 02:13 AM, n4buq wrote:


I see where Table 4-1, Item 3 (Signal Standardizer Calibration Fixture) states
that "Calibrated 7000-series plug-in units with suitable signal sources may be
substituted if lower performance is acceptable."? I just don't quite see where
the instructions outline how to set those up in place of the standardizer -
particularly for low-frequency linearity and/or vertical high-frequency
compensation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 5:11:41 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
I remember now that this involves adjustment of the LF Compensation.? The
calibration steps for that calls for a standardizer fixture and I don't have
one of those.? Is there a way to make that adjustment without a standardizer
fixture?
 

Hi Barry , thank you for the reply . I had heard / seen it mentioned that it was LF compensation being way off causing this but like you I hesitate to just blindly adjust a pot and see if it makes a difference . I had looked at the circuit and seen that some of the pots one might be adjusting are in series with the dreaded tant capacitors , I wonder if with that effect when using the vert position control it means the tant cap is bad . I'll have to tweak the pot and see then maybe change the tant if none or not enough effect .
thank you?Brian (UK)

On Friday, 31 December 2021, 18:07:51 GMT, n4buq <n4buq@...> wrote:

Hi Brian,

I presume you're referring to the vertical positioning control and not the horizontal positioning control but I presume the vertical one.? I did not notice that made much, if any, difference.? I don't fully understand this but I think the waviness is caused by overshoot/undershoot of the beam as it jumps from the trace to the readout.? If that's the case, then I would think that different vertical positions of the trace would affect this.

Overall, I think I prefer the GATED setting (draws the readout after the traces); however, at least for the 7704A, there's a switch that selects which B slot drives the readout so one must choose one or the other and I'm pretty sure I'm going to forget that setting when I have just one time-base in the B position which will disable the readout.? Maybe not but for now, I'm going to leave it in the GATED position.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Brian via groups.io" <brianas1948@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 11:26:08 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry , I have been watching these postings with interest . One of my 7844's
has this or a remarkably similar problem . There is the wavy / jumping about
readout but in my case it is made worse by using the position control -- did
this happen with yours . I would be pleased to know how similar my case is and
maybe if its not the same there might be suggestions of where the problem might
be .
many thanks in advance for help from anyone reading this
Brian? (UK)

? ? On Friday, 31 December 2021, 17:16:11 GMT, n4buq <n4buq@...> wrote:

Hi Albert,

That works!? I was just hesitant to start changing the settings without knowing
more about what they affect.? Very nice to have the wavy readouts stable.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@...>
To: "tekscopes" <[email protected]>
Sent: Friday, December 31, 2021 6:53:41 AM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
Hi Barry,

For minimizing that wavy readout forget about the signal standardizer.? Display
your signal (calibrator or whatever) at full height (8 div) and the time base
for the most nervous readout. Then rotate R4465 (Vert. Amp.) for the best
setting (most quiet readout).
Note that this setting is also best for your ordinary signal response. If the
result is still unsatisfactory then perhaps a slight readjustment of R4453
might help (but remember the original setting, just in case).

Albert

On Fri, Dec 31, 2021 at 02:13 AM, n4buq wrote:


I see where Table 4-1, Item 3 (Signal Standardizer Calibration Fixture) states
that "Calibrated 7000-series plug-in units with suitable signal sources may be
substituted if lower performance is acceptable."? I just don't quite see where
the instructions outline how to set those up in place of the standardizer -
particularly for low-frequency linearity and/or vertical high-frequency
compensation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "n4buq" <n4buq@...>
To: "tekscopes" <[email protected]>
Sent: Thursday, December 30, 2021 5:11:41 PM
Subject: Re: [TekScopes] 7704A - Noise on sine-wave traces
I remember now that this involves adjustment of the LF Compensation.? The
calibration steps for that calls for a standardizer fixture and I don't have
one of those.? Is there a way to make that adjustment without a standardizer
fixture?





?


 

Hi Brian,

The spot has to jump from the current trace vertical position to the readout vertical position. The undershoot or overshoot will be a fixed percentage of the jump size. If you move the trace (waveform) further away from the readout position then in absolute sense the jumps (say between top trace to readout and bottom trace to readout) will increase - and so will their differences - and the wavy behavior will increase. It will also increase when you increase the displayed signal amplitude (with same vertical centering).
In your 7844 the trimmers to adjust are R1749 and R1764 (for Beam 1), see calibration step G-6e, page 5-33, "LF COMP 1" and "LF COMP 2". I think you'd best use the same setting for both, though I didn't see such mentioned at first reading.

Albert

On Fri, Dec 31, 2021 at 07:15 PM, Brian wrote:
Hi Barry , thank you for the reply . I had heard / seen it mentioned that it
was LF compensation being way off causing this but like you I hesitate to just
blindly adjust a pot and see if it makes a difference . I had looked at the
circuit and seen that some of the pots one might be adjusting are in series
with the dreaded tant capacitors , I wonder if with that effect when using the
vert position control it means the tant cap is bad . I'll have to tweak the
pot and see then maybe change the tant if none or not enough effect .
thank you?Brian (UK)

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