Topics

475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?


Albert <aodiversen@...>
 

Stan,

Maybe I overlooked something in previous posts, but I missed a few things.
Triggering worked with EXT input. I think that was because you applied a very large input amplitude, same as in the case of INT with 2 Vpp amplitude and 20 mV/div. In TRIG VIEW mode the input to U520 can be viewed at the CRT screen. Even without proper triggering you can judge the signal amplitude. I&#7743; not sure but I guess the TRIG VIEW signal and the original vertical input signal should have about the same amplitude at the CRT.
The TD characteristics drift over time. Before thinking of a shorted or open TD, first of all try readjusting the TD bias currents. CR566 switched 300 mV when applying an exaggerated input signal. That seems to indicate that CR566 is functioning normally. (I have never seen an intermittent TD.) Hence I would follow the calibration procedure to readjust at least R547 'A' Trig Symmetry and R565 'A' Trig Sensitivity.

Albert

--- In TekScopes@..., David wrote:

I think you would be better off using a triangle or sine wave as a
test signal so you can distinguish the TD changing state and the test
signal.

I noticed that the earlier oscilloscopes which use the same trigger
circuit like the 465 and 464 have more detailed schematics which show
voltage levels and waveforms. They also show the details of U520 and
U720 (they are paraphase amplifiers used to selectively invert the
trigger signal which selects the slope) although that is not really
needed.

On Mon, 28 Jan 2013 04:45:35 -0000, "stan_katz"
wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan


--- In TekScopes@..., "Max Mazza" wrote:



--- In TekScopes@..., "stan_katz" wrote:

I've uncovered what I think is a significant symptom. If I inject a 1 volt square wave, at 1khz or above, set v/div to 20mv/div, and play with the position control, I can get the trigger source lamp to light. If I try the same stunt with a sine wave, I need at least 500khz to get the scope to trigger. This symptom seems to play into what Max was suggesting by lifting one lead of a tunnel diode, and then determining if I can get trigger with high slew rate sources. Of course, with the scope setup to the above test conditions, it's useless.

Stan
This was exactly the same behavior I noted when debugging my 3B4 timebase unit. With 1 KHz square wave of adequate amplitude, the triggers works. With a sinewave, it must be 100 KHz or above to trigger, with difficult.
If disconnecting the TD the behavior is exactly the same, assume that 99% the TD is open.

To get a definitive certainty, you should check if some signal is present on the anode of TD (with TD in place). If the amplitude swing during the TD's commutation is around 200-300mV pk-pk, the TD is OK. If a few mV, the TD is shorted. If more than 500mV, the TD is open.
Do that check before you detach one TD's lead and then after.
Compare the results.
Let us know.

Max


unclebanjoman
 

I've checked the schematic, "A' trigger generator".
The anode of CR556 should steps to about + 500mV. It's thearming diode.
Once it switches in high voltage state, then CR566 can commutate.
CR566 also steps to + 500mV

From your measurements, I conclude that CR556 is surely good, but CR566 not. The TD commutation is of the type you observe on CR556: clean, steep rising to +500 mV

Remember that CR566 switches only AFTER CR556 switches.
If a pulse reaches CR566 with CR556 still in low voltage state, CR566 doesn't commutates.

I hope that, since you have written the voltages with the - (minus) sign, you simply have made a mistake....

The "A trig sensitivity" simply regulates the quiescent point for both diodes. In low voltage state, it should be presumably around a few tens of mV.

You can play with R565 (with NO signal applied to scope inputs) to observe that increasing the voltage (rotating (slowly!) the pot toward the +5V TDs should commutate in their high voltage state, while rotating toward the -8V should restore their levels to +5/80 mV or so.

You have the 475 schematics, I presume. See schematic page 5 for more details.

CR566 can be supposed open, not only shorted. In the open case, you can equally observe a dirty pulse like your, because is the TD that makes (generates) the steep voltage swing of +0.5V. This is precisely the reason for which TDs are used.

Max

--- In TekScopes@..., "stan_katz" wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan


unclebanjoman
 

IMO CR556 is surely good.
To check CR566, gently pull out the anode lead, then observe the signal directly on the collector of Q566, and note if there are differences that before.

Max


Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan


Albert <aodiversen@...>
 

Could CR566 start to oscillate for some reason? If CR566 is shortcut or passive restive or open then the 300 mV signal at CR566 can't be explained. When the 6 mA supplied to CR566 after the switch of C556 does not produce a measurable signal at CR566, then an additional current switch in Q566 (less than 10 mA) will not produce 300 mV across CR566.

Albert

--- In TekScopes@..., "Max Mazza" wrote:


I've checked the schematic, "A' trigger generator".
The anode of CR556 should steps to about + 500mV. It's thearming diode.
Once it switches in high voltage state, then CR566 can commutate.
CR566 also steps to + 500mV

From your measurements, I conclude that CR556 is surely good, but CR566 not. The TD commutation is of the type you observe on CR556: clean, steep rising to +500 mV

Remember that CR566 switches only AFTER CR556 switches.
If a pulse reaches CR566 with CR556 still in low voltage state, CR566 doesn't commutates.

I hope that, since you have written the voltages with the - (minus) sign, you simply have made a mistake....

The "A trig sensitivity" simply regulates the quiescent point for both diodes. In low voltage state, it should be presumably around a few tens of mV.

You can play with R565 (with NO signal applied to scope inputs) to observe that increasing the voltage (rotating (slowly!) the pot toward the +5V TDs should commutate in their high voltage state, while rotating toward the -8V should restore their levels to +5/80 mV or so.

You have the 475 schematics, I presume. See schematic page 5 for more details.

CR566 can be supposed open, not only shorted. In the open case, you can equally observe a dirty pulse like your, because is the TD that makes (generates) the steep voltage swing of +0.5V. This is precisely the reason for which TDs are used.

Max


--- In TekScopes@..., "stan_katz" wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan


unclebanjoman
 

Yes Albert, I've taken into account that but, since the Stan's scope has only a mere 4 MHz bandwidth, I cannot be sure if he can see some strange oscillations on CR566...
Tek recommends a scope with almost 100MHz bandwidth to view and/or calibrate the signals in the trigger section.
Anyway, disconnecting the TD is a decisive method to see if there are differences before and after, avoiding loss of time.

Max

--- In TekScopes@..., "Albert" wrote:

Could CR566 start to oscillate for some reason? If CR566 is shortcut or passive restive or open then the 300 mV signal at CR566 can't be explained. When the 6 mA supplied to CR566 after the switch of C556 does not produce a measurable signal at CR566, then an additional current switch in Q566 (less than 10 mA) will not produce 300 mV across CR566.

Albert


unclebanjoman
 

Though on that 300 mV, actually if CR566 was open, there should be no more than a few tens of mV...
Mumble.... I'm scratching my head now....
Max


stan_katz
 

Yes, Max, you're right. I moved to the second channel of my student scope and could slow down the free running trace (this little scope never could trigger below 1v sig.) and note that these are positive 500mv pulses on CR556, and now I see a different situation than first reported on CR566. CR566 has a positive DC offset of about 200mv on top of which are riding 200mv pulses. These pulses vary in width depending on the attenuation. As attenuation is increased these riding pulses decrease in duration until the point (.1v/div) at which time the signal vanishes and trig lamp extinguishes. Pulse duration remains constant on CR556. I was able to stablize student scope channel 1 to duplicate this picture, so I'm now confident this is the real picture. I used a 2v p-p 1khz triangle wave input signal, as Dave suggested, this time around.

As for observing anodes while adjusting R565, CR556 kept commutating, and CR566 remained dead. Are you sure it's R565 I was to play with?

Max, I hear you on the need for a better scope to diagnose my 475. Can you recommend a used scope I can find on Ebay that I can get for under, say $350.00? In the meantime, it seems that my next move is to pull out the cathode lead of CR566 and report on anode signals, as the change in signal level should be detectable on the student scope, and answer the tunnel diode question once and for all. Right?


Stan

--- In TekScopes@..., "Albert" wrote:

Could CR566 start to oscillate for some reason? If CR566 is shortcut or passive restive or open then the 300 mV signal at CR566 can't be explained. When the 6 mA supplied to CR566 after the switch of C556 does not produce a measurable signal at CR566, then an additional current switch in Q566 (less than 10 mA) will not produce 300 mV across CR566.

Albert

--- In TekScopes@..., "Max Mazza" wrote:


I've checked the schematic, "A' trigger generator".
The anode of CR556 should steps to about + 500mV. It's thearming diode.
Once it switches in high voltage state, then CR566 can commutate.
CR566 also steps to + 500mV

From your measurements, I conclude that CR556 is surely good, but CR566 not. The TD commutation is of the type you observe on CR556: clean, steep rising to +500 mV

Remember that CR566 switches only AFTER CR556 switches.
If a pulse reaches CR566 with CR556 still in low voltage state, CR566 doesn't commutates.

I hope that, since you have written the voltages with the - (minus) sign, you simply have made a mistake....

The "A trig sensitivity" simply regulates the quiescent point for both diodes. In low voltage state, it should be presumably around a few tens of mV.

You can play with R565 (with NO signal applied to scope inputs) to observe that increasing the voltage (rotating (slowly!) the pot toward the +5V TDs should commutate in their high voltage state, while rotating toward the -8V should restore their levels to +5/80 mV or so.

You have the 475 schematics, I presume. See schematic page 5 for more details.

CR566 can be supposed open, not only shorted. In the open case, you can equally observe a dirty pulse like your, because is the TD that makes (generates) the steep voltage swing of +0.5V. This is precisely the reason for which TDs are used.

Max


--- In TekScopes@..., "stan_katz" wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan


stan_katz
 

R565 is right, after all. I had scope in "auto", should have been in "norm". Both diodes start comutating at the same time when advancing R565.

Stan

--- In TekScopes@..., "stan_katz" wrote:



Yes, Max, you're right. I moved to the second channel of my student scope and could slow down the free running trace (this little scope never could trigger below 1v sig.) and note that these are positive 500mv pulses on CR556, and now I see a different situation than first reported on CR566. CR566 has a positive DC offset of about 200mv on top of which are riding 200mv pulses. These pulses vary in width depending on the attenuation. As attenuation is increased these riding pulses decrease in duration until the point (.1v/div) at which time the signal vanishes and trig lamp extinguishes. Pulse duration remains constant on CR556. I was able to stablize student scope channel 1 to duplicate this picture, so I'm now confident this is the real picture. I used a 2v p-p 1khz triangle wave input signal, as Dave suggested, this time around.

As for observing anodes while adjusting R565, CR556 kept commutating, and CR566 remained dead. Are you sure it's R565 I was to play with?

Max, I hear you on the need for a better scope to diagnose my 475. Can you recommend a used scope I can find on Ebay that I can get for under, say $350.00? In the meantime, it seems that my next move is to pull out the cathode lead of CR566 and report on anode signals, as the change in signal level should be detectable on the student scope, and answer the tunnel diode question once and for all. Right?


Stan

--- In TekScopes@..., "Albert" wrote:

Could CR566 start to oscillate for some reason? If CR566 is shortcut or passive restive or open then the 300 mV signal at CR566 can't be explained. When the 6 mA supplied to CR566 after the switch of C556 does not produce a measurable signal at CR566, then an additional current switch in Q566 (less than 10 mA) will not produce 300 mV across CR566.

Albert

--- In TekScopes@..., "Max Mazza" wrote:


I've checked the schematic, "A' trigger generator".
The anode of CR556 should steps to about + 500mV. It's thearming diode.
Once it switches in high voltage state, then CR566 can commutate.
CR566 also steps to + 500mV

From your measurements, I conclude that CR556 is surely good, but CR566 not. The TD commutation is of the type you observe on CR556: clean, steep rising to +500 mV

Remember that CR566 switches only AFTER CR556 switches.
If a pulse reaches CR566 with CR556 still in low voltage state, CR566 doesn't commutates.

I hope that, since you have written the voltages with the - (minus) sign, you simply have made a mistake....

The "A trig sensitivity" simply regulates the quiescent point for both diodes. In low voltage state, it should be presumably around a few tens of mV.

You can play with R565 (with NO signal applied to scope inputs) to observe that increasing the voltage (rotating (slowly!) the pot toward the +5V TDs should commutate in their high voltage state, while rotating toward the -8V should restore their levels to +5/80 mV or so.

You have the 475 schematics, I presume. See schematic page 5 for more details.

CR566 can be supposed open, not only shorted. In the open case, you can equally observe a dirty pulse like your, because is the TD that makes (generates) the steep voltage swing of +0.5V. This is precisely the reason for which TDs are used.

Max


--- In TekScopes@..., "stan_katz" wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan


stan_katz
 

I've noticed a more than 10 fold improvement in triggering since adjusting R565. Scope now triggers on a sine wave with attenuator at .5v/div. and trigger slope cranked all the way over clockwise. My Army 475 manual doesn't seem to have "A trigger sensitivity" or "A trigger symmetry" calibration instructions. However I didn't notice any improvement adjusting R547 from nominal. The CR566 waveform is no longer as previously reported. It is still not a clean signal, as CR556 is. CR566 is still suspect although not as a failed TD, but rather degraded and out of spec part...still working up the courage to lift a lead.

Stan

--- In TekScopes@..., "stan_katz" wrote:

R565 is right, after all. I had scope in "auto", should have been in "norm". Both diodes start comutating at the same time when advancing R565.

Stan


--- In TekScopes@..., "stan_katz" wrote:



Yes, Max, you're right. I moved to the second channel of my student scope and could slow down the free running trace (this little scope never could trigger below 1v sig.) and note that these are positive 500mv pulses on CR556, and now I see a different situation than first reported on CR566. CR566 has a positive DC offset of about 200mv on top of which are riding 200mv pulses. These pulses vary in width depending on the attenuation. As attenuation is increased these riding pulses decrease in duration until the point (.1v/div) at which time the signal vanishes and trig lamp extinguishes. Pulse duration remains constant on CR556. I was able to stablize student scope channel 1 to duplicate this picture, so I'm now confident this is the real picture. I used a 2v p-p 1khz triangle wave input signal, as Dave suggested, this time around.

As for observing anodes while adjusting R565, CR556 kept commutating, and CR566 remained dead. Are you sure it's R565 I was to play with?

Max, I hear you on the need for a better scope to diagnose my 475. Can you recommend a used scope I can find on Ebay that I can get for under, say $350.00? In the meantime, it seems that my next move is to pull out the cathode lead of CR566 and report on anode signals, as the change in signal level should be detectable on the student scope, and answer the tunnel diode question once and for all. Right?


Stan

--- In TekScopes@..., "Albert" wrote:

Could CR566 start to oscillate for some reason? If CR566 is shortcut or passive restive or open then the 300 mV signal at CR566 can't be explained. When the 6 mA supplied to CR566 after the switch of C556 does not produce a measurable signal at CR566, then an additional current switch in Q566 (less than 10 mA) will not produce 300 mV across CR566.

Albert

--- In TekScopes@..., "Max Mazza" wrote:


I've checked the schematic, "A' trigger generator".
The anode of CR556 should steps to about + 500mV. It's thearming diode.
Once it switches in high voltage state, then CR566 can commutate.
CR566 also steps to + 500mV

From your measurements, I conclude that CR556 is surely good, but CR566 not. The TD commutation is of the type you observe on CR556: clean, steep rising to +500 mV

Remember that CR566 switches only AFTER CR556 switches.
If a pulse reaches CR566 with CR556 still in low voltage state, CR566 doesn't commutates.

I hope that, since you have written the voltages with the - (minus) sign, you simply have made a mistake....

The "A trig sensitivity" simply regulates the quiescent point for both diodes. In low voltage state, it should be presumably around a few tens of mV.

You can play with R565 (with NO signal applied to scope inputs) to observe that increasing the voltage (rotating (slowly!) the pot toward the +5V TDs should commutate in their high voltage state, while rotating toward the -8V should restore their levels to +5/80 mV or so.

You have the 475 schematics, I presume. See schematic page 5 for more details.

CR566 can be supposed open, not only shorted. In the open case, you can equally observe a dirty pulse like your, because is the TD that makes (generates) the steep voltage swing of +0.5V. This is precisely the reason for which TDs are used.

Max


--- In TekScopes@..., "stan_katz" wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan


unclebanjoman
 

You're are on the good way!!!!!!

The voltage on both TD's must be about 0 V.

You've observed a + 500mV on CR556. O.K.

CR566 seems completely off settled. The quiescent point should be 0V, not 200 mV.
R565 is the regulation trimmer for that quiescent point. Try to regulate to about 0V ,slightly positive voltage on anode of CR566. There's a point where the trigger sensitivity is good for very little signals on input too.

The calibration procedure on Tek manual is somewhat complicated, but you can find, with trial-and-error procedure, a quiescent point, for CR566, that triggers with almost any signal. Remember that the quiescent point should be between 50 and 80 mV or so, based on my experience with TD.

Try this first, before to proceed to lift a lead. At this point, CR566 seems O.K.

The purpose of R547 and R534 is to calibrate the zero point level for the trigger in respect to the position of the front panel control, TRIGGER LEVEL. I suggest do not touch these two trims, for now.

To achieve a full calibration of trigger section, I recommend to get a complete 475 service manual. I have a pdf copy of standard, non-military TEk 475 downloaded from ebama. Seems strange that the copy you owns this procedure is not described. Are you sure?

Max

--- In TekScopes@..., "stan_katz" wrote:

I've noticed a more than 10 fold improvement in triggering since adjusting R565. Scope now triggers on a sine wave with attenuator at .5v/div. and trigger slope cranked all the way over clockwise. My Army 475 manual doesn't seem to have "A trigger sensitivity" or "A trigger symmetry" calibration instructions. However I didn't notice any improvement adjusting R547 from nominal. The CR566 waveform is no longer as previously reported. It is still not a clean signal, as CR556 is. CR566 is still suspect although not as a failed TD, but rather degraded and out of spec part...still working up the courage to lift a lead.

Stan


 

I found a couple of much better and complete 475 service manuals. You
may want to go through the trigger adjustment procedures on page 5-18
before risking any tunnel diodes. Do not let the equipment
requirements or setup dissuade you as you can certainly complete it if
you can generate sine or triangle waveforms from 0.35 to 2 divisions.

I am kind of tempted to grab a 465 or similar with tunnel diode
problems just to see if I can fabricate replacements using a Schmitt
comparator circuit. I have been studying the 475/465 design and doing
some schematic doodles and believe I could replace a tunnel diode with
2 transistors plus external biasing.

Tektronix has the 475 service manual available here although you need
to register with them:

http://www.tek.com/manual/475

The KO4BB manual is excellent also but larger in size:

http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_475_Oscilloscope


On Tue, 29 Jan 2013 02:59:40 -0000, "stan_katz" <stan_katz@...>
wrote:

I've noticed a more than 10 fold improvement in triggering since adjusting R565. Scope now triggers on a sine wave with attenuator at .5v/div. and trigger slope cranked all the way over clockwise. My Army 475 manual doesn't seem to have "A trigger sensitivity" or "A trigger symmetry" calibration instructions. However I didn't notice any improvement adjusting R547 from nominal. The CR566 waveform is no longer as previously reported. It is still not a clean signal, as CR556 is. CR566 is still suspect although not as a failed TD, but rather degraded and out of spec part...still working up the courage to lift a lead.

Stan

--- In TekScopes@..., "stan_katz" wrote:

R565 is right, after all. I had scope in "auto", should have been in "norm". Both diodes start comutating at the same time when advancing R565.

Stan


--- In TekScopes@..., "stan_katz" wrote:



Yes, Max, you're right. I moved to the second channel of my student scope and could slow down the free running trace (this little scope never could trigger below 1v sig.) and note that these are positive 500mv pulses on CR556, and now I see a different situation than first reported on CR566. CR566 has a positive DC offset of about 200mv on top of which are riding 200mv pulses. These pulses vary in width depending on the attenuation. As attenuation is increased these riding pulses decrease in duration until the point (.1v/div) at which time the signal vanishes and trig lamp extinguishes. Pulse duration remains constant on CR556. I was able to stablize student scope channel 1 to duplicate this picture, so I'm now confident this is the real picture. I used a 2v p-p 1khz triangle wave input signal, as Dave suggested, this time around.

As for observing anodes while adjusting R565, CR556 kept commutating, and CR566 remained dead. Are you sure it's R565 I was to play with?

Max, I hear you on the need for a better scope to diagnose my 475. Can you recommend a used scope I can find on Ebay that I can get for under, say $350.00? In the meantime, it seems that my next move is to pull out the cathode lead of CR566 and report on anode signals, as the change in signal level should be detectable on the student scope, and answer the tunnel diode question once and for all. Right?


Stan

--- In TekScopes@..., "Albert" wrote:

Could CR566 start to oscillate for some reason? If CR566 is shortcut or passive restive or open then the 300 mV signal at CR566 can't be explained. When the 6 mA supplied to CR566 after the switch of C556 does not produce a measurable signal at CR566, then an additional current switch in Q566 (less than 10 mA) will not produce 300 mV across CR566.

Albert

--- In TekScopes@..., "Max Mazza" wrote:


I've checked the schematic, "A' trigger generator".
The anode of CR556 should steps to about + 500mV. It's thearming diode.
Once it switches in high voltage state, then CR566 can commutate.
CR566 also steps to + 500mV

From your measurements, I conclude that CR556 is surely good, but CR566 not. The TD commutation is of the type you observe on CR556: clean, steep rising to +500 mV

Remember that CR566 switches only AFTER CR556 switches.
If a pulse reaches CR566 with CR556 still in low voltage state, CR566 doesn't commutates.

I hope that, since you have written the voltages with the - (minus) sign, you simply have made a mistake....

The "A trig sensitivity" simply regulates the quiescent point for both diodes. In low voltage state, it should be presumably around a few tens of mV.

You can play with R565 (with NO signal applied to scope inputs) to observe that increasing the voltage (rotating (slowly!) the pot toward the +5V TDs should commutate in their high voltage state, while rotating toward the -8V should restore their levels to +5/80 mV or so.

You have the 475 schematics, I presume. See schematic page 5 for more details.

CR566 can be supposed open, not only shorted. In the open case, you can equally observe a dirty pulse like your, because is the TD that makes (generates) the steep voltage swing of +0.5V. This is precisely the reason for which TDs are used.

Max


--- In TekScopes@..., "stan_katz" wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan



------------------------------------

Yahoo! Groups Links



unclebanjoman
 

Another thing: since che 475 and 465 circuits are very very similar (I own a 465), the waveform on CR566 in effect is more dirty than CR556. It should rensemble the waveform of CR556 with superimposed a train of spikes a few mV high on the upper portion of the waveform.
In any case, during the commutation, the voltage swing on anode of CR566 MUST be around 500mV. No less, no more.
Both 465 and 475 Tek manuals stated that.

Max


Albert <aodiversen@...>
 

I wouldn't call it dirty. What you see is merely the effect of the 1 kHz TD current variation (from Q556/Q566) while both TDs are stable in their high state. It just happened that CR566 shows a larger ripple. With a change in trigger Level CR556 might have the largest ripple.

Stan, your "student" 'scope isn't very trustfully it seems. So why not perform DC measurements, simply with a DMM? Triggering at Norm, Slope +, no signal input, very slow sweep speed, Hold Off at maximum. Arming and firing events forced by rotating Level cw and ccw respectively. Only Holdoff might still last too short for a DMM, but is also less interesting since the TD voltages are determined then by transistor saturation.
If you generate a sweep by rotating Level ccw and leave Level in that position, then after the next Holdoff period both TDs will stay in there low state (but a few mV higher than during Holdoff). Next rotating Level cw will switch CR556 in the high state. Then also CR566 will jump a few mV higher (be "armed") but still not switch. Finally, rotating Level ccw will force CR566 to switch to the high state and the sweep starts. Then also CR556 will jump a few mV higher and remain stable in it's high state. At the end of the sweep both TDs get reset to their low states by the Holdoff circuit.
I don't have my 465 open to check voltages but I feel quite sure that the description is correct.

Albert

Another thing: since che 475 and 465 circuits are very very similar (I own a 465), the waveform on CR566 in effect is more dirty than CR556. It should rensemble the waveform of CR556 with superimposed a train of spikes a few mV high on the upper portion of the waveform.
In any case, during the commutation, the voltage swing on anode of CR566 MUST be around 500mV. No less, no more.
Both 465 and 475 Tek manuals stated that.

Max


unclebanjoman
 

Wow Albert,
your description is very precise and exactly what I already know.
My compliments to you!
I had described the situation in a very simplified manner to avoid getting Stan into confusion...

Max


stan_katz
 

I've finally downloaded REAL Tek 457 manual. MUCH better manual. Thanks Dave. Max, I think I've fiddled with R565 to get the best sensitivity possible. That is + trigger slope cranked fully clockwise, and max attenuation possible of .5v/div. I'll keep on trying to do better. I might try to upload sketches of the waveforms I now have to Archive 2. It would be easier to just email. Can I get permission to email direct?..Max?..Dave? As for detecting +80mv on my little D51, that's a stretch. Do my best tho.

Stan

Stan

Stan

--- In TekScopes@..., David wrote:

I found a couple of much better and complete 475 service manuals. You
may want to go through the trigger adjustment procedures on page 5-18
before risking any tunnel diodes. Do not let the equipment
requirements or setup dissuade you as you can certainly complete it if
you can generate sine or triangle waveforms from 0.35 to 2 divisions.

I am kind of tempted to grab a 465 or similar with tunnel diode
problems just to see if I can fabricate replacements using a Schmitt
comparator circuit. I have been studying the 475/465 design and doing
some schematic doodles and believe I could replace a tunnel diode with
2 transistors plus external biasing.

Tektronix has the 475 service manual available here although you need
to register with them:

http://www.tek.com/manual/475

The KO4BB manual is excellent also but larger in size:

http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_475_Oscilloscope


On Tue, 29 Jan 2013 02:59:40 -0000, "stan_katz"
wrote:

I've noticed a more than 10 fold improvement in triggering since adjusting R565. Scope now triggers on a sine wave with attenuator at .5v/div. and trigger slope cranked all the way over clockwise. My Army 475 manual doesn't seem to have "A trigger sensitivity" or "A trigger symmetry" calibration instructions. However I didn't notice any improvement adjusting R547 from nominal. The CR566 waveform is no longer as previously reported. It is still not a clean signal, as CR556 is. CR566 is still suspect although not as a failed TD, but rather degraded and out of spec part...still working up the courage to lift a lead.

Stan

--- In TekScopes@..., "stan_katz" wrote:

R565 is right, after all. I had scope in "auto", should have been in "norm". Both diodes start comutating at the same time when advancing R565.

Stan


--- In TekScopes@..., "stan_katz" wrote:



Yes, Max, you're right. I moved to the second channel of my student scope and could slow down the free running trace (this little scope never could trigger below 1v sig.) and note that these are positive 500mv pulses on CR556, and now I see a different situation than first reported on CR566. CR566 has a positive DC offset of about 200mv on top of which are riding 200mv pulses. These pulses vary in width depending on the attenuation. As attenuation is increased these riding pulses decrease in duration until the point (.1v/div) at which time the signal vanishes and trig lamp extinguishes. Pulse duration remains constant on CR556. I was able to stablize student scope channel 1 to duplicate this picture, so I'm now confident this is the real picture. I used a 2v p-p 1khz triangle wave input signal, as Dave suggested, this time around.

As for observing anodes while adjusting R565, CR556 kept commutating, and CR566 remained dead. Are you sure it's R565 I was to play with?

Max, I hear you on the need for a better scope to diagnose my 475. Can you recommend a used scope I can find on Ebay that I can get for under, say $350.00? In the meantime, it seems that my next move is to pull out the cathode lead of CR566 and report on anode signals, as the change in signal level should be detectable on the student scope, and answer the tunnel diode question once and for all. Right?


Stan

--- In TekScopes@..., "Albert" wrote:

Could CR566 start to oscillate for some reason? If CR566 is shortcut or passive restive or open then the 300 mV signal at CR566 can't be explained. When the 6 mA supplied to CR566 after the switch of C556 does not produce a measurable signal at CR566, then an additional current switch in Q566 (less than 10 mA) will not produce 300 mV across CR566.

Albert

--- In TekScopes@..., "Max Mazza" wrote:


I've checked the schematic, "A' trigger generator".
The anode of CR556 should steps to about + 500mV. It's thearming diode.
Once it switches in high voltage state, then CR566 can commutate.
CR566 also steps to + 500mV

From your measurements, I conclude that CR556 is surely good, but CR566 not. The TD commutation is of the type you observe on CR556: clean, steep rising to +500 mV

Remember that CR566 switches only AFTER CR556 switches.
If a pulse reaches CR566 with CR556 still in low voltage state, CR566 doesn't commutates.

I hope that, since you have written the voltages with the - (minus) sign, you simply have made a mistake....

The "A trig sensitivity" simply regulates the quiescent point for both diodes. In low voltage state, it should be presumably around a few tens of mV.

You can play with R565 (with NO signal applied to scope inputs) to observe that increasing the voltage (rotating (slowly!) the pot toward the +5V TDs should commutate in their high voltage state, while rotating toward the -8V should restore their levels to +5/80 mV or so.

You have the 475 schematics, I presume. See schematic page 5 for more details.

CR566 can be supposed open, not only shorted. In the open case, you can equally observe a dirty pulse like your, because is the TD that makes (generates) the steep voltage swing of +0.5V. This is precisely the reason for which TDs are used.

Max


--- In TekScopes@..., "stan_katz" wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan



------------------------------------

Yahoo! Groups Links



 

Those manuals are a big improvement over the military manual I was
using.

The trigger level controls are just that. They set the point on the
waveform where the triggers occur. Sensitivity is exclusively
controlled by internal adjustment R565 for the A trigger and R785 for
the B trigger.

The internal trigger centering adjustments, R534 and R754, trim the
trigger level controls so that at midpoint, the trigger levels are
centered vertically on the CRT.

The internal trigger symmetry adjustments, R547 and R767, trim the
trigger circuits so that the trigger levels do not change when the
slopes are swapped between positive and negative.

The outputs from Q556 and Q566 are differential, one current falls
while the other rises, positive currents into the tunnel diodes. When
you measure the voltage from each tunnel diode to ground, the voltage
will jump from about 65mV to 500mV when each diode triggers. That
transition point happens at about 10mA. The A and B sweep generators
compare the tunnel diode voltage outputs to about 200mV.

You are welcome to email scans or pictures to me and I can host them
and provide links. I am not very fond of Yahoo's picture hosting
myself.

On Wed, 30 Jan 2013 01:24:44 -0000, "stan_katz" <stan_katz@...>
wrote:

I've finally downloaded REAL Tek 457 manual. MUCH better manual. Thanks Dave. Max, I think I've fiddled with R565 to get the best sensitivity possible. That is + trigger slope cranked fully clockwise, and max attenuation possible of .5v/div. I'll keep on trying to do better. I might try to upload sketches of the waveforms I now have to Archive 2. It would be easier to just email. Can I get permission to email direct?..Max?..Dave? As for detecting +80mv on my little D51, that's a stretch. Do my best tho.

Stan

--- In TekScopes@..., David wrote:

I found a couple of much better and complete 475 service manuals. You
may want to go through the trigger adjustment procedures on page 5-18
before risking any tunnel diodes. Do not let the equipment
requirements or setup dissuade you as you can certainly complete it if
you can generate sine or triangle waveforms from 0.35 to 2 divisions.

I am kind of tempted to grab a 465 or similar with tunnel diode
problems just to see if I can fabricate replacements using a Schmitt
comparator circuit. I have been studying the 475/465 design and doing
some schematic doodles and believe I could replace a tunnel diode with
2 transistors plus external biasing.

Tektronix has the 475 service manual available here although you need
to register with them:

http://www.tek.com/manual/475

The KO4BB manual is excellent also but larger in size:

http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_475_Oscilloscope


On Tue, 29 Jan 2013 02:59:40 -0000, "stan_katz"
wrote:

I've noticed a more than 10 fold improvement in triggering since adjusting R565. Scope now triggers on a sine wave with attenuator at .5v/div. and trigger slope cranked all the way over clockwise. My Army 475 manual doesn't seem to have "A trigger sensitivity" or "A trigger symmetry" calibration instructions. However I didn't notice any improvement adjusting R547 from nominal. The CR566 waveform is no longer as previously reported. It is still not a clean signal, as CR556 is. CR566 is still suspect although not as a failed TD, but rather degraded and out of spec part...still working up the courage to lift a lead.

Stan

--- In TekScopes@..., "stan_katz" wrote:

R565 is right, after all. I had scope in "auto", should have been in "norm". Both diodes start comutating at the same time when advancing R565.

Stan


unclebanjoman
 

If you finally have a good and decent copy of the manual, you can finally do the work in a right manner.
The page relevant to you should be 5-40 and followings.
However I recommend to pause and read carefully the manual first, then proceed calmly.

The best sensitivity when adjusting R565 should be checked with the trigger level position to 0, not full clockwise, anyway. Fully clockwise implies that you raises the trigger level very above 0 V. The level spans from -8V to +5.2V. In normal operation the trigger level should be near 0. You can vary trigger level only if you knows what you are doing.... for instance, when there are noisy signals, they can generate spurious or false triggering; in that case it's obvious to raise the trigger level just above 0 level, up to the point where a stable waveform can be displayed.

Moreover, if you have touched R534 (A trig centering), it's easy that you have altered the 0 level for the trigger level knob....

Conclusion: study carefully the manual first, then resume the process on your 475. The calibration procedures are somewhat complicated in some cases, and they require a lot of patience and calm.
No problem if you want to contact me directly, but I think that it's better that you post your questions here, since "many brains are better tha one :-)

Don't rely strong on my suggestion to read +80mV, it's an extreme simplification to help you to make your scope functioning with the instrumentation in your possess. Read the manual first, then ask with no problem!

Max

--- In TekScopes@..., "stan_katz" wrote:

I've finally downloaded REAL Tek 457 manual. MUCH better manual. Thanks Dave. Max, I think I've fiddled with R565 to get the best sensitivity possible. That is + trigger slope cranked fully clockwise, and max attenuation possible of .5v/div. I'll keep on trying to do better. I might try to upload sketches of the waveforms I now have to Archive 2. It would be easier to just email. Can I get permission to email direct?..Max?..Dave? As for detecting +80mv on my little D51, that's a stretch. Do my best tho.

Stan

Stan

Stan


stan_katz
 

I can study the manual. What I can't do is figure out what cabling and interface devices I need. What's a 50ohm 5ns GR cable (GR stands for General Radio?). What's a 50ohm signal pickoff unit, GR to BNC adapter, X10 attenuator (a standalone cabled inline attenuator??). Sorry I'm so dense here, but I need help to cobble together whatever is alluded to here. All I have is a signal generator, and a bunch of 50ohm cables. I have a feeling if I were a ham radio guy, the above stuff would be obvious. Maybe someone can post Ebay links to whatever it is I should order. In the meantime, I'll continue to do my homework reading the manual.

Stan

--- In TekScopes@..., "Max Mazza" wrote:

If you finally have a good and decent copy of the manual, you can finally do the work in a right manner.
The page relevant to you should be 5-40 and followings.
However I recommend to pause and read carefully the manual first, then proceed calmly.

The best sensitivity when adjusting R565 should be checked with the trigger level position to 0, not full clockwise, anyway. Fully clockwise implies that you raises the trigger level very above 0 V. The level spans from -8V to +5.2V. In normal operation the trigger level should be near 0. You can vary trigger level only if you knows what you are doing.... for instance, when there are noisy signals, they can generate spurious or false triggering; in that case it's obvious to raise the trigger level just above 0 level, up to the point where a stable waveform can be displayed.

Moreover, if you have touched R534 (A trig centering), it's easy that you have altered the 0 level for the trigger level knob....

Conclusion: study carefully the manual first, then resume the process on your 475. The calibration procedures are somewhat complicated in some cases, and they require a lot of patience and calm.
No problem if you want to contact me directly, but I think that it's better that you post your questions here, since "many brains are better tha one :-)

Don't rely strong on my suggestion to read +80mV, it's an extreme simplification to help you to make your scope functioning with the instrumentation in your possess. Read the manual first, then ask with no problem!

Max

--- In TekScopes@..., "stan_katz" wrote:

I've finally downloaded REAL Tek 457 manual. MUCH better manual. Thanks Dave. Max, I think I've fiddled with R565 to get the best sensitivity possible. That is + trigger slope cranked fully clockwise, and max attenuation possible of .5v/div. I'll keep on trying to do better. I might try to upload sketches of the waveforms I now have to Archive 2. It would be easier to just email. Can I get permission to email direct?..Max?..Dave? As for detecting +80mv on my little D51, that's a stretch. Do my best tho.

Stan

Stan

Stan


 

That is why I said in an earlier post, "Do not let the equipment
requirements or setup dissuade you as you can certainly complete it if
you can generate sine or triangle waveforms from 0.35 to 2 divisions."

All you need to do is connect the signal or function generator to the
channel 1 or channel 2 input with a short BNC patch cable and produce
a 50 kHz to 350 kHz sine or triangle wave with a CRT deflection of
0.35 divisions to 2 or 3 divisions. The vertical volts/div settings
are relatively unimportant because the internal trigger circuits see
exactly what is displayed on the CRT.

I would not worry about the external trigger calibration until you
verify that the internal trigger is working correctly and even then,
all that is really needed is a BNC T-connector to use as a splitter
and maybe an attenuator.

On Thu, 31 Jan 2013 00:23:28 -0000, "stan_katz" <stan_katz@...>
wrote:

I can study the manual. What I can't do is figure out what cabling and interface devices I need. What's a 50ohm 5ns GR cable (GR stands for General Radio?). What's a 50ohm signal pickoff unit, GR to BNC adapter, X10 attenuator (a standalone cabled inline attenuator??). Sorry I'm so dense here, but I need help to cobble together whatever is alluded to here. All I have is a signal generator, and a bunch of 50ohm cables. I have a feeling if I were a ham radio guy, the above stuff would be obvious. Maybe someone can post Ebay links to whatever it is I should order. In the meantime, I'll continue to do my homework reading the manual.

Stan

--- In TekScopes@..., "Max Mazza" wrote:

If you finally have a good and decent copy of the manual, you can finally do the work in a right manner.
The page relevant to you should be 5-40 and followings.
However I recommend to pause and read carefully the manual first, then proceed calmly.

The best sensitivity when adjusting R565 should be checked with the trigger level position to 0, not full clockwise, anyway. Fully clockwise implies that you raises the trigger level very above 0 V. The level spans from -8V to +5.2V. In normal operation the trigger level should be near 0. You can vary trigger level only if you knows what you are doing.... for instance, when there are noisy signals, they can generate spurious or false triggering; in that case it's obvious to raise the trigger level just above 0 level, up to the point where a stable waveform can be displayed.

Moreover, if you have touched R534 (A trig centering), it's easy that you have altered the 0 level for the trigger level knob....

Conclusion: study carefully the manual first, then resume the process on your 475. The calibration procedures are somewhat complicated in some cases, and they require a lot of patience and calm.
No problem if you want to contact me directly, but I think that it's better that you post your questions here, since "many brains are better tha one :-)

Don't rely strong on my suggestion to read +80mV, it's an extreme simplification to help you to make your scope functioning with the instrumentation in your possess. Read the manual first, then ask with no problem!

Max

--- In TekScopes@..., "stan_katz" wrote:

I've finally downloaded REAL Tek 457 manual. MUCH better manual. Thanks Dave. Max, I think I've fiddled with R565 to get the best sensitivity possible. That is + trigger slope cranked fully clockwise, and max attenuation possible of .5v/div. I'll keep on trying to do better. I might try to upload sketches of the waveforms I now have to Archive 2. It would be easier to just email. Can I get permission to email direct?..Max?..Dave? As for detecting +80mv on my little D51, that's a stretch. Do my best tho.

Stan

Stan

Stan



------------------------------------

Yahoo! Groups Links



stan_katz
 

Dave,

I got it now.

Thanks,

Stan

--- In TekScopes@..., David wrote:

That is why I said in an earlier post, "Do not let the equipment
requirements or setup dissuade you as you can certainly complete it if
you can generate sine or triangle waveforms from 0.35 to 2 divisions."

All you need to do is connect the signal or function generator to the
channel 1 or channel 2 input with a short BNC patch cable and produce
a 50 kHz to 350 kHz sine or triangle wave with a CRT deflection of
0.35 divisions to 2 or 3 divisions. The vertical volts/div settings
are relatively unimportant because the internal trigger circuits see
exactly what is displayed on the CRT.

I would not worry about the external trigger calibration until you
verify that the internal trigger is working correctly and even then,
all that is really needed is a BNC T-connector to use as a splitter
and maybe an attenuator.

On Thu, 31 Jan 2013 00:23:28 -0000, "stan_katz"
wrote:

I can study the manual. What I can't do is figure out what cabling and interface devices I need. What's a 50ohm 5ns GR cable (GR stands for General Radio?). What's a 50ohm signal pickoff unit, GR to BNC adapter, X10 attenuator (a standalone cabled inline attenuator??). Sorry I'm so dense here, but I need help to cobble together whatever is alluded to here. All I have is a signal generator, and a bunch of 50ohm cables. I have a feeling if I were a ham radio guy, the above stuff would be obvious. Maybe someone can post Ebay links to whatever it is I should order. In the meantime, I'll continue to do my homework reading the manual.

Stan

--- In TekScopes@..., "Max Mazza" wrote:

If you finally have a good and decent copy of the manual, you can finally do the work in a right manner.
The page relevant to you should be 5-40 and followings.
However I recommend to pause and read carefully the manual first, then proceed calmly.

The best sensitivity when adjusting R565 should be checked with the trigger level position to 0, not full clockwise, anyway. Fully clockwise implies that you raises the trigger level very above 0 V. The level spans from -8V to +5.2V. In normal operation the trigger level should be near 0. You can vary trigger level only if you knows what you are doing.... for instance, when there are noisy signals, they can generate spurious or false triggering; in that case it's obvious to raise the trigger level just above 0 level, up to the point where a stable waveform can be displayed.

Moreover, if you have touched R534 (A trig centering), it's easy that you have altered the 0 level for the trigger level knob....

Conclusion: study carefully the manual first, then resume the process on your 475. The calibration procedures are somewhat complicated in some cases, and they require a lot of patience and calm.
No problem if you want to contact me directly, but I think that it's better that you post your questions here, since "many brains are better tha one :-)

Don't rely strong on my suggestion to read +80mV, it's an extreme simplification to help you to make your scope functioning with the instrumentation in your possess. Read the manual first, then ask with no problem!

Max

--- In TekScopes@..., "stan_katz" wrote:

I've finally downloaded REAL Tek 457 manual. MUCH better manual. Thanks Dave. Max, I think I've fiddled with R565 to get the best sensitivity possible. That is + trigger slope cranked fully clockwise, and max attenuation possible of .5v/div. I'll keep on trying to do better. I might try to upload sketches of the waveforms I now have to Archive 2. It would be easier to just email. Can I get permission to email direct?..Max?..Dave? As for detecting +80mv on my little D51, that's a stretch. Do my best tho.

Stan

Stan

Stan



------------------------------------

Yahoo! Groups Links