Topics

468 DSO B timebase triggering

Colin Herbert
 

Hi,
I am a bit confused by the triggering of the B time-base on my 468. I have the original manuals (vols. 1&2) and the section on Triggering starts on P 4-49. Figure 4-4 shows a setup for checking the triggering of both A and B time-bases but I don't possess CT-3 50-ohm Signal Pickoff Unit. I simply started out ignoring the accessories connecting to the external trigger inputs and connected two 50-ohm cables from my SG-501 to the Ch1 and Ch2 inputs, using 50-ohm terminations on each input.
I can get the A -time-base triggering to check out fine, but the B time-base doesn't seem to want to trigger at all with the recommended control settings. This may just be because the B Trigger sensitivity (R154) needs setting correctly, but this is a bit of a complex instrument and I don't want to go barging in and messing anything up further. Activating the beam-finder shows a vertical signal, but no time-base.
I can get a delayed B time-base using the normal control settings, but not the B time-base triggered in "NORM".
Any ideas or suggestions before I go take a look at R154?
Colin.

 

Colin,
Check to see if you have more than one transition on the display.If the delayed sweep is in "runs after delay" mode, the delayed sweep will start as soon as the selected delay has elapsed.In "trigger after delay" mode, it waits until the delay has elapsed & then it looks for a trigger.If the trigger doesn't happen, then you will see nothing.
If you display a time mark generator:"Run" mode will produce a smooth, continuous horizontal "scroll" of the waveform."Trig" mode will wait for the delay to elapse & then the intensified zone will "snap" to the next input which satisfies the trigger level.This mode is intended to remove jitter from the display.
 HankC, Boston WA1HOS

Colin Herbert
 

I have just noticed some other strange behaviour. I can get the B time-base
to trigger sometimes from a 5 division peak-to-peak, 1kHz square-wave into
Ch1. It can be persuaded to trigger with the B trigger coupling in HF-reject
or LF-reject, but the last full cycle is "cycling" slowly in intensity.
Similar triggering with the last cycle varying in intensity can also be got
to by "flicking" the coupling switch when in the AC POSITION.

Colin.



From: TekScopes@... [mailto:TekScopes@...]
Sent: 18 January 2017 19:53
To: TekScopes@...
Subject: [TekScopes] 468 DSO B timebase triggering





Hi,
I am a bit confused by the triggering of the B time-base on my 468. I have
the original manuals (vols. 1&2) and the section on Triggering starts on P
4-49. Figure 4-4 shows a setup for checking the triggering of both A and B
time-bases but I don't possess CT-3 50-ohm Signal Pickoff Unit. I simply
started out ignoring the accessories connecting to the external trigger
inputs and connected two 50-ohm cables from my SG-501 to the Ch1 and Ch2
inputs, using 50-ohm terminations on each input.
I can get the A -time-base triggering to check out fine, but the B time-base
doesn't seem to want to trigger at all with the recommended control
settings. This may just be because the B Trigger sensitivity (R154) needs
setting correctly, but this is a bit of a complex instrument and I don't
want to go barging in and messing anything up further. Activating the
beam-finder shows a vertical signal, but no time-base.
I can get a delayed B time-base using the normal control settings, but not
the B time-base triggered in "NORM".
Any ideas or suggestions before I go take a look at R154?
Colin.





_____

No virus found in this message.
Checked by AVG - www.avg.com <http://www.avg.com/email-signature>
Version: 2016.0.7996 / Virus Database: 4749/13756 - Release Date: 01/12/17

 

On 18 Jan 2017 11:53:10 -0800, you wrote:

Hi,
I am a bit confused by the triggering of the B time-base on my 468. I have the original manuals (vols. 1&2) and the section on Triggering starts on P 4-49. Figure 4-4 shows a setup for checking the triggering of both A and B time-bases but I don't possess CT-3 50-ohm Signal Pickoff Unit. I simply started out ignoring the accessories connecting to the external trigger inputs and connected two 50-ohm cables from my SG-501 to the Ch1 and Ch2 inputs, using 50-ohm terminations on each input.
I can get the A -time-base triggering to check out fine, but the B time-base doesn't seem to want to trigger at all with the recommended control settings. This may just be because the B Trigger sensitivity (R154) needs setting correctly, but this is a bit of a complex instrument and I don't want to go barging in and messing anything up further. Activating the beam-finder shows a vertical signal, but no time-base.
I can get a delayed B time-base using the normal control settings, but not the B time-base triggered in "NORM".
Any ideas or suggestions before I go take a look at R154?
Colin.
Tektronix is using the CT-3 and x10 attenuator as another splitter so
that 4 roughly time aligned signals are produced; they could be
replaced with another BNC-T. I usually do these procedures with one
splitter while moving the two outputs between two oscilloscope inputs
as needed.

On Thu, 19 Jan 2017 11:44:13 -0000, you wrote:

I have just noticed some other strange behaviour. I can get the B time-base
to trigger sometimes from a 5 division peak-to-peak, 1kHz square-wave into
Ch1. It can be persuaded to trigger with the B trigger coupling in HF-reject
or LF-reject, but the last full cycle is "cycling" slowly in intensity.
Similar triggering with the last cycle varying in intensity can also be got
to by "flicking" the coupling switch when in the AC POSITION.

Colin.
It might just be a case of Q230 which buffers the trigger B input
being damaged.

Colin Herbert
 

Hi,

Thanks for this useful info, David. I thought something like this was the
situation. I assume that the x10 attenuator is there because the CT-3
pick-off voltage is 10% of the through signal and so all inputs will get
pretty much the same level of signal.



Hank: I don't really follow what you are stating - the B time-base source
switch has "starts after delay", "norm", "CH1" ,"CH2" and "EXT" positions;
there is no "Trigger After Delay" position.



I don't know what I was up to when I started this thread, because in the
cold light of day everything seems to check out ok according to the manual.
However, the "cycling" in intensity of the last full cycle of the 1kHz
square-wave still happens, but only when the horizontal display is "B
DELY'D", A triggering is "NORM" with the trigger level control fully
clockwise, B triggering is at "NORM" and adjusted to give a (relatively)
stable display with the B-trigger level and the A and B time-bases are set
to the same time (0.5ms is ok, making the time shorter increases the rate
of the intensity "cycling" and vice versa; changing to a faster B time-base
rate results in a display without the intensity "cycling"). Adjusting the
"Delay Time Position" multi-turn control results in the intensity "cycling"
remaining with the last full cycle, but the whole horizontal scan is
shortened from the right side going toward the left. Could this all be
caused by a damaged Q230? (Aargh, I hope not - they are a matched pair of
FETs and probably unobtainium).



I have to say that, apart from this being a complex piece of kit, the manual
can be confusing, to say the least, in places. Page 4-49 is the beginning of
the "Triggering" section and refers to adjustment locations 2 and 3, but
they are, in fact, 4 and 5. If only one function needs checking, it is
necessary to go through all of the other earlier function checks to get the
controls to the right settings. I suppose this saves a lot of extra "Set"
sections for each function, but it does involve a lot of ploughing through
earlier parts of the manual.



Colin.

From: TekScopes@... [mailto:TekScopes@...]
Sent: 19 January 2017 13:12
To: TekScopes@...
Subject: Re: [TekScopes] 468 DSO B timebase triggering




Tektronix is using the CT-3 and x10 attenuator as another splitter so
that 4 roughly time aligned signals are produced; they could be
replaced with another BNC-T. I usually do these procedures with one
splitter while moving the two outputs between two oscilloscope inputs
as needed.

On Thu, 19 Jan 2017 11:44:13 -0000, you wrote:

I have just noticed some other strange behaviour. I can get the B time-base
to trigger sometimes from a 5 division peak-to-peak, 1kHz square-wave into
Ch1. It can be persuaded to trigger with the B trigger coupling in
HF-reject
or LF-reject, but the last full cycle is "cycling" slowly in intensity.
Similar triggering with the last cycle varying in intensity can also be got
to by "flicking" the coupling switch when in the AC POSITION.

Colin.
It might just be a case of Q230 which buffers the trigger B input
being damaged.



_____

No virus found in this message.
Checked by AVG - www.avg.com <http://www.avg.com/email-signature>
Version: 2016.0.7996 / Virus Database: 4749/13756 - Release Date: 01/12/17

Tom Gardner
 

On 20/01/17 16:33, 'Colin Herbert' colingherbert@... [TekScopes] wrote:

I don't know what I was up to when I started this thread, because in the
cold light of day everything seems to check out ok according to the manual.
However, the "cycling" in intensity of the last full cycle of the 1kHz
square-wave still happens, but only when the horizontal display is "B
DELY'D", A triggering is "NORM" with the trigger level control fully
clockwise, B triggering is at "NORM" and adjusted to give a (relatively)
stable display with the B-trigger level and the A and B time-bases are set
to the same time (0.5ms is ok, making the time shorter increases the rate
of the intensity "cycling" and vice versa; changing to a faster B time-base
rate results in a display without the intensity "cycling"). Adjusting the
"Delay Time Position" multi-turn control results in the intensity "cycling"
remaining with the last full cycle, but the whole horizontal scan is
shortened from the right side going toward the left. Could this all be
caused by a damaged Q230? (Aargh, I hope not - they are a matched pair of
FETs and probably unobtainium).
I'm not sure what you mean by "intensity cycling", but the intensified region is the region that will be displayed when you select the horizontal display to be "B delayed". It is usual for the B timebase to be faster than the A timebase, so it acts as a "time zoom".

Check the A trig holdoff is "norm"

Does something simple work, e.g. typical use cases
- select
--horizontal display to A timebase only
--B trigger B starts after delay
--delay time to midrange, say 5
--A trig holdoff to "norm"; definitely not "B ends A"

- observe the cal out, and get a few cycles displayed; there should be no intensity variation
- adjust the B timebase knob to be 1/10 the time per division of the A timebase (i.e. 10* faster)
- select horizontal display A intensified
- you should see
--1/10 of the trace being brighter, somewhere near the middle of the trace
--changing the delay time should smoothly move the intensified region

- adjust the intensified region so it straddles a transition; remember where in the intensified region the transition is
- select horizontal display to "B delayed"
- you should see the transition at the "same" place
- change the delay time
- you should see the transition move in the "opposite" direction
- flick between A intensified and B delayed to understand why

 

On Fri, 20 Jan 2017 16:33:04 -0000, you wrote:

Hi,

Thanks for this useful info, David. I thought something like this was the
situation. I assume that the x10 attenuator is there because the CT-3
pick-off voltage is 10% of the through signal and so all inputs will get
pretty much the same level of signal.
Exactly. The levels do not need to be matched but if they are roughly
close, it makes things easier.

...

I don't know what I was up to when I started this thread, because in the
cold light of day everything seems to check out ok according to the manual.
However, the "cycling" in intensity of the last full cycle of the 1kHz
square-wave still happens, but only when the horizontal display is "B
DELY'D", A triggering is "NORM" with the trigger level control fully
clockwise, B triggering is at "NORM" and adjusted to give a (relatively)
stable display with the B-trigger level and the A and B time-bases are set
to the same time (0.5ms is ok, making the time shorter increases the rate
of the intensity "cycling" and vice versa; changing to a faster B time-base
rate results in a display without the intensity "cycling"). Adjusting the
"Delay Time Position" multi-turn control results in the intensity "cycling"
remaining with the last full cycle, but the whole horizontal scan is
shortened from the right side going toward the left. Could this all be
caused by a damaged Q230? (Aargh, I hope not - they are a matched pair of
FETs and probably unobtainium).
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
display?

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, the manual
can be confusing, to say the least, in places. Page 4-49 is the beginning of
the "Triggering" section and refers to adjustment locations 2 and 3, but
they are, in fact, 4 and 5. If only one function needs checking, it is
necessary to go through all of the other earlier function checks to get the
controls to the right settings. I suppose this saves a lot of extra "Set"
sections for each function, but it does involve a lot of ploughing through
earlier parts of the manual.

Colin.
The 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.

Colin Herbert
 

Ok,

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
with this.

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!

Colin.



From: TekScopes@... [mailto:TekScopes@...]
Sent: 20 January 2017 17:10
To: TekScopes@...
Subject: Re: [TekScopes] 468 DSO B timebase triggering





On Fri, 20 Jan 2017 16:33:04 -0000, you wrote:

Hi,

Thanks for this useful info, David. I thought something like this was the
situation. I assume that the x10 attenuator is there because the CT-3
pick-off voltage is 10% of the through signal and so all inputs will get
pretty much the same level of signal.
Exactly. The levels do not need to be matched but if they are roughly
close, it makes things easier.

...

I don't know what I was up to when I started this thread, because in the
cold light of day everything seems to check out ok according to the manual.
However, the "cycling" in intensity of the last full cycle of the 1kHz
square-wave still happens, but only when the horizontal display is "B
DELY'D", A triggering is "NORM" with the trigger level control fully
clockwise, B triggering is at "NORM" and adjusted to give a (relatively)
stable display with the B-trigger level and the A and B time-bases are set
to the same time (0.5ms is ok, making the time shorter increases the rate
of the intensity "cycling" and vice versa; changing to a faster B time-base
rate results in a display without the intensity "cycling"). Adjusting the
"Delay Time Position" multi-turn control results in the intensity "cycling"
remaining with the last full cycle, but the whole horizontal scan is
shortened from the right side going toward the left. Could this all be
caused by a damaged Q230? (Aargh, I hope not - they are a matched pair of
FETs and probably unobtainium).
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
display?

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, the
manual
can be confusing, to say the least, in places. Page 4-49 is the beginning
of
the "Triggering" section and refers to adjustment locations 2 and 3, but
they are, in fact, 4 and 5. If only one function needs checking, it is
necessary to go through all of the other earlier function checks to get the
controls to the right settings. I suppose this saves a lot of extra "Set"
sections for each function, but it does involve a lot of ploughing through
earlier parts of the manual.

Colin.
The 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.



_____

No virus found in this message.
Checked by AVG - www.avg.com <http://www.avg.com/email-signature>
Version: 2016.0.7998 / Virus Database: 4749/13802 - Release Date: 01/20/17

 

It may be that the readout is causing the blank spots.It is written by the same CRT gun, so the beam can't be in 2 places at once.Try turning the readout off & see if the gaps go away.
 HankC, Boston WA1HOS

[Non-text portions of this message have been removed]

Colin Herbert
 

Are you by any chance confusing my 468 with a 7-k series? As far as I know, there isn’t a 400-series with readout. The readout feature was something that first impressed me about my 7623A after collecting a few 400-series initially.

Colin.



From: TekScopes@... [mailto:TekScopes@...]
Sent: 23 January 2017 15:52
To: TekScopes@...
Subject: [TekScopes] Re: 468 DSO B timebase triggering





It may be that the readout is causing the blank spots.It is written by the same CRT gun, so the beam can't be in 2 places at once.Try turning the readout off & see if the gaps go away.
HankC, Boston WA1HOS

[Non-text portions of this message have been removed]



_____

No virus found in this message.
Checked by AVG - www.avg.com <http://www.avg.com/email-signature>
Version: 2016.0.7998 / Virus Database: 4749/13802 - Release Date: 01/20/17



[Non-text portions of this message have been removed]

 

My bad; I was thinking of my 2445.
 HankC, Boston WA1HOS

[Non-text portions of this message have been removed]

 

It actually was not such an odd mistake to make. I had to double
check to see if the 468 which is a combination analog oscilloscope and
DSO has no readout because the follow on series of oscilloscopes, the
22xx series, had readouts in the combination analog and DSO models.
The schematics show that the 2230 is based on the 468.

Can the 468 display its cursors in analog mode? That would produce
the same problem.

On Tue, 24 Jan 2017 00:45:24 +0000 (UTC), you wrote:

My bad; I was thinking of my 2445.

HankC, Boston WA1HOS

Colin Herbert
 

Hi,

I think I may have solved this, now. I Did some calibration checks and
adjusted A-Sweep Start & A-Sweep Calibration, as well B-Sweep High-speed
timing adjustment. (No other calibration adjustments seemed too bad to me).
The result is now that the Delay Time Position control really does go from
zero delay time and that I don't see the odd effect on the last full cycle
under the conditions I described before. Under those conditions the
horizontal sweep now seems fine and the effect of the Delay Time Position
control is to shorten the horizontal sweep from the right, getting down to
just less than one division as the control is turned clockwise.

Colin.



From: TekScopes@... [mailto:TekScopes@...]
Sent: 21 January 2017 16:10
To: TekScopes@...
Subject: RE: [TekScopes] 468 DSO B timebase triggering





Ok,

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
with this.

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!

Colin.

From: TekScopes@... [mailto:TekScopes@...]
Sent: 20 January 2017 17:10
To: TekScopes@...
Subject: Re: [TekScopes] 468 DSO B timebase triggering

On Fri, 20 Jan 2017 16:33:04 -0000, you wrote:

Hi,

Thanks for this useful info, David. I thought something like this was the
situation. I assume that the x10 attenuator is there because the CT-3
pick-off voltage is 10% of the through signal and so all inputs will get
pretty much the same level of signal.
Exactly. The levels do not need to be matched but if they are roughly
close, it makes things easier.

...

I don't know what I was up to when I started this thread, because in the
cold light of day everything seems to check out ok according to the manual.
However, the "cycling" in intensity of the last full cycle of the 1kHz
square-wave still happens, but only when the horizontal display is "B
DELY'D", A triggering is "NORM" with the trigger level control fully
clockwise, B triggering is at "NORM" and adjusted to give a (relatively)
stable display with the B-trigger level and the A and B time-bases are set
to the same time (0.5ms is ok, making the time shorter increases the rate
of the intensity "cycling" and vice versa; changing to a faster B time-base
rate results in a display without the intensity "cycling"). Adjusting the
"Delay Time Position" multi-turn control results in the intensity "cycling"
remaining with the last full cycle, but the whole horizontal scan is
shortened from the right side going toward the left. Could this all be
caused by a damaged Q230? (Aargh, I hope not - they are a matched pair of
FETs and probably unobtainium).
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
display?

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, the
manual
can be confusing, to say the least, in places. Page 4-49 is the beginning
of
the "Triggering" section and refers to adjustment locations 2 and 3, but
they are, in fact, 4 and 5. If only one function needs checking, it is
necessary to go through all of the other earlier function checks to get the
controls to the right settings. I suppose this saves a lot of extra "Set"
sections for each function, but it does involve a lot of ploughing through
earlier parts of the manual.

Colin.
The 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.

_____

No virus found in this message.
Checked by AVG - www.avg.com <http://www.avg.com/email-signature>
Version: 2016.0.7998 / Virus Database: 4749/13802 - Release Date: 01/20/17





_____

No virus found in this message.
Checked by AVG - www.avg.com <http://www.avg.com/email-signature>
Version: 2016.0.7998 / Virus Database: 4749/13802 - Release Date: 01/20/17