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New user with 465 needs help

david
 

My name is Dave, I joined your group because I have a 465 scope that has a issue with channel 2. All my repair work has been on Tube Amps, Marshall & Fender, and on Stereo Amps. I am not familiar with analog scopes,I have a 1052B digital that I use frequently. Channel 1 & Channel 2 on the 465  match well with each other at 1Khz, I can overlay the traces with each other and they match. Also agrees with the 1052B, but as I increase the frequency of my test signal from 1Khz to 4Mhz Channel 2 shows a decrease in amplitude of about 400 mV less at 4Mhz. Channel 1 appears to be OK,  it is close to the readings on the 1052B. The wave forms are identical, only difference is the amplitude. Low voltage power supplies check good, all test voltage readings on the vertical preamp board checked OK except for the zero volt reading at the emitter of transistor Q262. Shows +10 mV, test wave forms on vertical preamp board checked OK except waveform number 19  which is also on the emitter of Q262, checks low, is less than one division. Manual shows 3 1/2 divisions. Hoping someone has had this problem and can help.
Dave

 

Hi Dave, welcome to Tektronix Anonymous.

What effect does the Invert switch have on channel 2?

Can you run your test at 5mV/div where all of the attenuators are
switched out?

Also verify that AC and DC coupling produce identical results from 1
kHz to 4 MHz.

How are you connecting your signal source to the oscilloscope?
Directly with a coaxial cable? Are you using a 50 ohm termination at
the oscilloscope?

Are you using a sine or square wave for testing? Does the low
frequency square wave response *look* square and identical and
channels 1 and 2?

The output from the emitter of Q262 goes to the internal trigger
circuits and has no effect on what is displayed unless you use the
trigger view function. That it is low and channel 1 displays
correctly just indicates that the problem is likely before this point.

On Sat, 24 Sep 2016 18:24:26 +0000 (UTC), you wrote:

My name is Dave, I joined your group because I have a 465 scope that has a issue with channel 2. All my repair work has been on Tube Amps, Marshall & Fender, and on Stereo Amps. I am not familiar with analog scopes,I have a 1052B digital that I use frequently. Channel 1 & Channel 2 on the 465  match well with each other at 1Khz, I can overlay the traces with each other and they match. Also agrees with the 1052B, but as I increase the frequency of my test signal from 1Khz to 4Mhz Channel 2 shows a decrease in amplitude of about 400 mV less at 4Mhz. Channel 1 appears to be OK,  it is close to the readings on the 1052B. The wave forms are identical, only difference is the amplitude. Low voltage power supplies check good, all test voltage readings on the vertical preamp board checked OK except for the zero volt reading at the emitter of transistor Q262. Shows +10 mV, test wave forms on vertical preamp board checked OK except waveform number 19  which is also on the emitter of Q262,
checks low, is less than one division. Manual shows 3 1/2 divisions. Hoping someone has had this problem and can help.
Dave

david
 

Hi Dave, thanks for the welcome, Invert switch works correctly,I am using a square wave for testing. I was connected to signal generator with a Tee, one three foot 50 ohm cable with BNC connectors on both ends to scope and one from Tee to counter. Then I had a Tee on the counter with another three foot 50 ohm BNC cable to channel two. Noticed channel two trace was fuzzy, switched cables, channel one was fuzzy, What is the correct way to connect generator to scope?I eliminated the counter hookup, connected one three foot cable to generator, other end to a tee and then two from tee to channel one and two. Ran my test at 5mV/div and all wave forms are identical, overlay one and two and they match perfectly. No difference in results between AC and DC coupling. Low frequency Square waves look "square". The voltage on emitter of Q262, may be from my fluorescent lights, When lights are on, and trigger source is set to channel 2, with Trigger mode set to Normal, they trigger a trace. Electronic ballasts! All other V/div ranges show difference between channels, Channel one shows no change in amplitude up to 4Mhz, Channel two at 4 Mhz is reduced 30% vertical, frequency of signals is good in all ranges, just the amplitude is bad.

From: "David @DWH [TekScopes]" <TekScopes@...>e
To: TekScopes@...
Sent: Saturday, September 24, 2016 3:39 PM
Subject: Re: [TekScopes] New user with 465 needs help

  Hi Dave, welcome to Tektronix Anonymous.

What effect does the Invert switch have on channel 2?

Can you run your test at 5mV/div where all of the attenuators are
switched out?

Also verify that AC and DC coupling produce identical results from 1
kHz to 4 MHz.

How are you connecting your signal source to the oscilloscope?
Directly with a coaxial cable? Are you using a 50 ohm termination at
the oscilloscope?

Are you using a sine or square wave for testing? Does the low
frequency square wave response *look* square and identical and
channels 1 and 2?

The output from the emitter of Q262 goes to the internal trigger
circuits and has no effect on what is displayed unless you use the
trigger view function. That it is low and channel 1 displays
correctly just indicates that the problem is likely before this point.

On Sat, 24 Sep 2016 18:24:26 +0000 (UTC), you wrote:

My name is Dave, I joined your group because I have a 465 scope that has a issue with channel 2. All my repair work has been on Tube Amps, Marshall & Fender, and on Stereo Amps. I am not familiar with analog scopes,I have a 1052B digital that I use frequently. Channel 1 & Channel 2 on the 465  match well with each other at 1Khz, I can overlay the traces with each other and they match. Also agrees with the 1052B, but as I increase the frequency of my test signal from 1Khz to 4Mhz Channel 2 shows a decrease in amplitude of about 400 mV less at 4Mhz. Channel 1 appears to be OK,  it is close to the readings on the 1052B. The wave forms are identical, only difference is the amplitude. Low voltage power supplies check good, all test voltage readings on the vertical preamp board checked OK except for the zero volt reading at the emitter of transistor Q262. Shows +10 mV, test wave forms on vertical preamp board checked OK except waveform number 19  which is also on the emitter of Q262,
checks low, is less than one division. Manual shows 3 1/2 divisions. Hoping someone has had this problem and can help.
Dave
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Bob Albert
 

I have been playing with electronics test equipment for about three quarters of a century and only relatively recently have realized the importance of test cable termination.
If connecting a coaxial line directly to an oscilloscope input, there should be a termination at the 'scope input that matches the line.  If you are using a probe that has high impedance, you still need the proper termination on the cable.
Reflections cause errors of many types, not the least of which is waveform distortion, especially when the length of cable is an appreciable fraction of a wavelength of any frequency component of interest.  When observing sinusoids it's deceptive because it's only the amplitude that seems wrong.  With complex waves, it's a more sophisticated distortion.
A tee is a potential troublemaker, since it won't present the same signal to both cables and it will interfere with impedance matching.  Even if both cables are terminated correctly, the tee parallels them and thus the source cable is incorrectly terminated.

There is no substitute for understanding the ramifications of the test setup.  I am not pointing any fingers here, just stating some things that often get overlooked.
Bob

On Saturday, September 24, 2016 6:35 PM, "David davide_us@... [TekScopes]" <TekScopes@...> wrote:


  Hi Dave, thanks for the welcome, Invert switch works correctly,I am using a square wave for testing. I was connected to signal generator with a Tee, one three foot 50 ohm cable with BNC connectors on both ends to scope and one from Tee to counter. Then I had a Tee on the counter with another three foot 50 ohm BNC cable to channel two. Noticed channel two trace was fuzzy, switched cables, channel one was fuzzy, What is the correct way to connect generator to scope?I eliminated the counter hookup, connected one three foot cable to generator, other end to a tee and then two from tee to channel one and two. Ran my test at 5mV/div and all wave forms are identical, overlay one and two and they match perfectly. No difference in results between AC and DC coupling. Low frequency Square waves look "square". The voltage on emitter of Q262, may be from my fluorescent lights, When lights are on, and trigger source is set to channel 2, with Trigger mode set to Normal, they trigger a trace. Electronic ballasts! All other V/div ranges show difference between channels, Channel one shows no change in amplitude up to 4Mhz, Channel two at 4 Mhz is reduced 30% vertical, frequency of signals is good in all ranges, just the amplitude is bad.

From: "David @DWH [TekScopes]" <TekScopes@...>e
To: TekScopes@...
Sent: Saturday, September 24, 2016 3:39 PM
Subject: Re: [TekScopes] New user with 465 needs help

  Hi Dave, welcome to Tektronix Anonymous.

What effect does the Invert switch have on channel 2?

Can you run your test at 5mV/div where all of the attenuators are
switched out?

Also verify that AC and DC coupling produce identical results from 1
kHz to 4 MHz.

How are you connecting your signal source to the oscilloscope?
Directly with a coaxial cable? Are you using a 50 ohm termination at
the oscilloscope?

Are you using a sine or square wave for testing? Does the low
frequency square wave response *look* square and identical and
channels 1 and 2?

The output from the emitter of Q262 goes to the internal trigger
circuits and has no effect on what is displayed unless you use the
trigger view function. That it is low and channel 1 displays
correctly just indicates that the problem is likely before this point.

On Sat, 24 Sep 2016 18:24:26 +0000 (UTC), you wrote:

My name is Dave, I joined your group because I have a 465 scope that has a issue with channel 2. All my repair work has been on Tube Amps, Marshall & Fender, and on Stereo Amps. I am not familiar with analog scopes,I have a 1052B digital that I use frequently. Channel 1 & Channel 2 on the 465  match well with each other at 1Khz, I can overlay the traces with each other and they match. Also agrees with the 1052B, but as I increase the frequency of my test signal from 1Khz to 4Mhz Channel 2 shows a decrease in amplitude of about 400 mV less at 4Mhz. Channel 1 appears to be OK,  it is close to the readings on the 1052B. The wave forms are identical, only difference is the amplitude. Low voltage power supplies check good, all test voltage readings on the vertical preamp board checked OK except for the zero volt reading at the emitter of transistor Q262. Shows +10 mV, test wave forms on vertical preamp board checked OK except waveform number 19  which is also on the emitter of Q262,
checks low, is less than one division. Manual shows 3 1/2 divisions. Hoping someone has had this problem and can help.
Dave
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[Non-text portions of this message have been removed]

Brad Thompson <brad.thompson@...>
 

On 9/24/2016 9:31 PM, David davide_us@... [TekScopes] wrote:
<snip>

The voltage on emitter of Q262, may be from my fluorescent lights, When lights are on, and trigger source is set to channel 2, with Trigger mode set to Normal, they trigger a trace. Electronic ballasts!
<snip>

Hello--

Long shot time-- maybe the effect isn't due to magnetic-field pickup from the
lights. There's an uncommon effect.

It's also possible that one or more diodes are photosensitive. This occurred in older
diodes with painted bodies-- if the paint flaked away, light shining on the diode would
generate photocurrent that modulated (or DC-biased) whatever current was normally supposed
to flow through the diode.

You could use a piece of opaque cardboard as a light shield-- place it between
the circuit board and the light source.

Incidentally, some older-vintage transistors featured transparent glass-to-metal lead seals.
Shining light on the seals would affect the the transistor's operation. This showed up mostly
when the circuit was in its breadboard phase, with parts on long leads bent every which way.


73--

Brad AA1IP

 

Your test setup is not ideal but I doubt it is causing a problem.

Just to be clear, do the 5mV/div, 10mV/div, and 20mV/div ranges show
the change in amplitude at 4 MHz?

What the 5mV/div, 10mV/div, and 20mV/div ranges have in common is that
no high impedance attenuators are used before the input amplifier. The
x10 and x100 attenuator modules plug in so you might try reseating
them.

There is another easy test which you should do. Set the volts/div to
5mV/div. Short the BNC input; a 50 ohm terminator or x1 probe with
the ground clip connected to the tip will work as a short. Does the
trace shift between AC and DC coupling? This checks the leakage
current into the JFET.

The puzzling part of your description of the problem is that at 4 MHz
the square wave still looks square. If it showed tilt, high frequency
roll-off, or low frequency roll-off, then that would make more sense.

On Sun, 25 Sep 2016 12:20:48 +0000 (UTC), you wrote:

I ran another test and both channels match in 5mV/div range, 10mV/div range, and 20mV/div range. All the settings 50mV/div and above show errors. Could this be my test setup? My Tek 1052B digital shows no problems.
On Sun, 25 Sep 2016 01:31:59 +0000 (UTC), you wrote:

Hi Dave, thanks for the welcome, Invert switch works correctly,I am using a square wave for testing. I was connected to signal generator with a Tee, one three foot 50 ohm cable with BNC connectors on both ends to scope and one from Tee to counter. Then I had a Tee on the counter with another three foot 50 ohm BNC cable to channel two. Noticed channel two trace was fuzzy, switched cables, channel one was fuzzy, What is the correct way to connect generator to scope?I eliminated the counter hookup, connected one three foot cable to generator, other end to a tee and then two from tee to channel one and two. Ran my test at 5mV/div and all wave forms are identical, overlay one and two and they match perfectly. No difference in results between AC and DC coupling. Low frequency Square waves look "square". The voltage on emitter of Q262, may be from my fluorescent lights, When lights are on, and trigger source is set to channel 2, with Trigger mode set to Normal, they trigger a trace.
Electronic ballasts! All other V/div ranges show difference between channels, Channel one shows no change in amplitude up to 4Mhz, Channel two at 4 Mhz is reduced 30% vertical, frequency of signals is good in all ranges, just the amplitude is bad.

david
 

| Hi Dave, want to thank you guys for helping me. It appears my test setup is causing a lot of the distortion and all the attenuation on channel two.Too many connections and no 50 ohm Termination. Bob Albert sent me a link for a video, explained 50ohm termination. Hate to show my ignorance on the web for all to see but it helped. After all the checking, I sampled the signal from my generator with a 10x probe and all is well. No attenuation, Channel one and two match well, waveforms match my good scope also. I did find that the channel two connector on scope needed cleaned,is better now. I am going to get a 50 ohm feed through terminator and check again Only paid $91.00 for this 465, Still has issues though, occasionally when I turn on scope it runs for a minute or two, then I smell something, the trace starts to fade out and moves off the top of the screen. Turn off scope for a minute, turn it back on, and it will run for hours. Had it good and warm and it keeps working.Has done this 5 or 6 times now. Did it again today, do I have to wait till it fails to troubleshoot? Only other problem I have right now is the trigger mode switch needs cleaned, Auto & Normal modes work OK, Single sweep is not working. Don't need it because I have a good scope, may not mess with it. From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Tuesday, September 27, 2016 1:22 AM
Subject: Re: [TekScopes] New user with 465 needs help

Your test setup is not ideal but I doubt it is causing a problem.

Just to be clear, do the 5mV/div, 10mV/div, and 20mV/div ranges show
the change in amplitude at 4 MHz?

What the 5mV/div, 10mV/div, and 20mV/div ranges have in common is that
no high impedance attenuators are used before the input amplifier. The
x10 and x100 attenuator modules plug in so you might try reseating
them.

There is another easy test which you should do. Set the volts/div to
5mV/div. Short the BNC input; a 50 ohm terminator or x1 probe with
the ground clip connected to the tip will work as a short. Does the
trace shift between AC and DC coupling? This checks the leakage
current into the JFET.

The puzzling part of your description of the problem is that at 4 MHz
the square wave still looks square. If it showed tilt, high frequency
roll-off, or low frequency roll-off, then that would make more sense.

On Sun, 25 Sep 2016 12:20:48 +0000 (UTC), you wrote:

I ran another test and both channels match in 5mV/div range, 10mV/div range, and 20mV/div range. All the settings 50mV/div and above show errors. Could this be my test setup? My Tek 1052B digital shows no problems.
On Sun, 25 Sep 2016 01:31:59 +0000 (UTC), you wrote:

Hi Dave, thanks for the welcome, Invert switch works correctly,I am using a square wave for testing. I was connected to signal generator with a Tee, one three foot 50 ohm cable with BNC connectors on both ends to scope and one from Tee to counter. Then I had a Tee on the counter with another three foot 50 ohm BNC cable to channel two. Noticed channel two trace was fuzzy, switched cables, channel one was fuzzy, What is the correct way to connect generator to scope?I eliminated the counter hookup, connected one three foot cable to generator, other end to a tee and then two from tee to channel one and two. Ran my test at 5mV/div and all wave forms are identical, overlay one and two and they match perfectly. No difference in results between AC and DC coupling. Low frequency Square waves look "square". The voltage on emitter of Q262, may be from my fluorescent lights, When lights are on, and trigger source is set to channel 2, with Trigger mode set to Normal, they trigger a trace.
Electronic ballasts! All other V/div ranges show difference between channels, Channel one shows no change in amplitude up to 4Mhz, Channel two at 4 Mhz is reduced 30% vertical, frequency of signals is good in all ranges, just the amplitude is bad.

|

Only paid $91.00 for this 465, Still has issues though, occasionally when I turn on scope it runs for a minute or two, then I smell something, the trace starts to fade out and moves off the top of the screen. Turn off scope for a minute, turn it back on, and it will run for hours. Had it good and warm and it keeps working.Has done this 5 or 6 times now. Did it today, do I have to wait till it fails to troubleshoot? I am going to get a 50 ohm feed through terminator and check again.


From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Tuesday, September 27, 2016 1:22 AM
Subject: Re: [TekScopes] New user with 465 needs help

  Your test setup is not ideal but I doubt it is causing a problem.

Just to be clear, do the 5mV/div, 10mV/div, and 20mV/div ranges show
the change in amplitude at 4 MHz?

What the 5mV/div, 10mV/div, and 20mV/div ranges have in common is that
no high impedance attenuators are used before the input amplifier. The
x10 and x100 attenuator modules plug in so you might try reseating
them.

There is another easy test which you should do. Set the volts/div to
5mV/div. Short the BNC input; a 50 ohm terminator or x1 probe with
the ground clip connected to the tip will work as a short. Does the
trace shift between AC and DC coupling? This checks the leakage
current into the JFET.

The puzzling part of your description of the problem is that at 4 MHz
the square wave still looks square. If it showed tilt, high frequency
roll-off, or low frequency roll-off, then that would make more sense.

On Sun, 25 Sep 2016 12:20:48 +0000 (UTC), you wrote:

I ran another test and both channels match in 5mV/div range, 10mV/div range, and 20mV/div range. All the settings 50mV/div and above show errors. Could this be my test setup? My Tek 1052B digital shows no problems.
On Sun, 25 Sep 2016 01:31:59 +0000 (UTC), you wrote:

Hi Dave, thanks for the welcome, Invert switch works correctly,I am using a square wave for testing. I was connected to signal generator with a Tee, one three foot 50 ohm cable with BNC connectors on both ends to scope and one from Tee to counter. Then I had a Tee on the counter with another three foot 50 ohm BNC cable to channel two. Noticed channel two trace was fuzzy, switched cables, channel one was fuzzy, What is the correct way to connect generator to scope?I eliminated the counter hookup, connected one three foot cable to generator, other end to a tee and then two from tee to channel one and two. Ran my test at 5mV/div and all wave forms are identical, overlay one and two and they match perfectly. No difference in results between AC and DC coupling. Low frequency Square waves look "square". The voltage on emitter of Q262, may be from my fluorescent lights, When lights are on, and trigger source is set to channel 2, with Trigger mode set to Normal, they trigger a trace.
Electronic ballasts! All other V/div ranges show difference between channels, Channel one shows no change in amplitude up to 4Mhz, Channel two at 4 Mhz is reduced 30% vertical, frequency of signals is good in all ranges, just the amplitude is bad.
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Tom Gardner
 

For a 100MHz scope (e.g. a 465) and for these purposes you can get away with a stand 50ohm terminator and a BNC T connector. Of course, a feed-through terminator is nice to have for faster scopes.

May I suggest that you may benefit from understanding more of the distortions that can occur with "suboptimal" probing, e.g. a standard *10 probe and 6" ground lead will resonate at ~100MHz. Such resonances can be very visible when probing ordinary digital signals.

On 28/09/16 00:38, David davide_us@... [TekScopes] wrote:

I am going to get a 50 ohm feed through terminator and check again

 

On Tue, 27 Sep 2016 23:38:20 +0000 (UTC), you wrote:

| Hi Dave, want to thank you guys for helping me. It appears my test setup is causing a lot of the distortion and all the attenuation on channel two.Too many connections and no 50 ohm Termination. Bob Albert sent me a link for a video, explained 50ohm termination. Hate to show my ignorance on the web for all to see but it helped.
Vertical deflection calibration is usually done without 50 ohm
terminations because the tolerance of the 50 ohm terminations at both
ends adds to the calibration error.

With a termination problem at higher frequencies, I was expecting a
non-square waveform instead of a lower amplitude but good fidelity
waveform.

It often pays to do a sanity check by duplicating the test setup as
closely as possible for each channel when things are going weird.

After all the checking, I sampled the signal from my generator with a 10x probe and all is well. No attenuation, Channel one and two match well, waveforms match my good scope also. I did find that the channel two connector on scope needed cleaned,is better now. I am going to get a 50 ohm feed through terminator and check again
Up to almost 100 MHz you can get away with using a BNC-T adapter and a
normal terminator in place of a usually more expensive feed-through
terminator.

Only paid $91.00 for this 465, Still has issues though, occasionally when I turn on scope it runs for a minute or two, then I smell something, the trace starts to fade out and moves off the top of the screen. Turn off scope for a minute, turn it back on, and it will run for hours. Had it good and warm and it keeps working.Has done
this 5 or 6 times now. Did it again today, do I have to wait till it fails to troubleshoot? Only other problem I have right now is the trigger mode switch needs cleaned, Auto & Normal modes work OK, Single sweep is not working. Don't need it because I have a good scope, may not mess with it.
That is a reasonable price for a likely easy to repair and good
performance analog oscilloscope. With a full rebuild, it should
operate trouble free for years.

That sounds like it will be difficult to track down until the problem
gets worse. The power supply is pretty resilient to damage so I would
not worry too much about catastrophic failure.

What you might try is removing the case and making a close visual
inspection (mark 1 eyeball) of the dipped epoxy solid tantalum
capacitors and other parts in general for signs of overheating like
discoloration, cracking, or surface eruptions. Usually they fail as a
complete short but sometimes they just drop to a low but non-zero
resistance and act as little heaters. A test using your mark 1 nose
might find the problem area.

david
 

Well I'm back to where I started. Checking at 40kHz with 10x probe, square wave, the channels only match at .2V/div setting and below. At .5 V/div channel 1 shows 3 div., top of wave has a curve, is not flat. Channel 2 shows 2.4 div., and top and bottom of wave, is full 90 deg. segment of circle. All the settings above .5 V show channel 2 with the same distortion, and lower amplitude than channel 1. At 1V/div there is 1 div. diff. at 5V/div there is 2.5 div diff. At 1mHz to 4mHz Waveforms look the same, rounded off top and bottom, but channel 2 is 2 div. less amplitude than ch.1. Don't know how to proceed.


From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Wednesday, September 28, 2016 5:01 AM
Subject: Re: [TekScopes] New user with 465 needs help

  On Tue, 27 Sep 2016 23:38:20 +0000 (UTC), you wrote:

| Hi Dave, want to thank you guys for helping me. It appears my test setup is causing a lot of the distortion and all the attenuation on channel two.Too many connections and no 50 ohm Termination. Bob Albert sent me a link for a video, explained 50ohm termination. Hate to show my ignorance on the web for all to see but it helped.
Vertical deflection calibration is usually done without 50 ohm
terminations because the tolerance of the 50 ohm terminations at both
ends adds to the calibration error.

With a termination problem at higher frequencies, I was expecting a
non-square waveform instead of a lower amplitude but good fidelity
waveform.

It often pays to do a sanity check by duplicating the test setup as
closely as possible for each channel when things are going weird.

After all the checking, I sampled the signal from my generator with a 10x probe and all is well. No attenuation, Channel one and two match well, waveforms match my good scope also. I did find that the channel two connector on scope needed cleaned,is better now. I am going to get a 50 ohm feed through terminator and check again
Up to almost 100 MHz you can get away with using a BNC-T adapter and a
normal terminator in place of a usually more expensive feed-through
terminator.

Only paid $91.00 for this 465, Still has issues though, occasionally when I turn on scope it runs for a minute or two, then I smell something, the trace starts to fade out and moves off the top of the screen. Turn off scope for a minute, turn it back on, and it will run for hours. Had it good and warm and it keeps working.Has done
this 5 or 6 times now. Did it again today, do I have to wait till it fails to troubleshoot? Only other problem I have right now is the trigger mode switch needs cleaned, Auto & Normal modes work OK, Single sweep is not working. Don't need it because I have a good scope, may not mess with it.
That is a reasonable price for a likely easy to repair and good
performance analog oscilloscope. With a full rebuild, it should
operate trouble free for years.

That sounds like it will be difficult to track down until the problem
gets worse. The power supply is pretty resilient to damage so I would
not worry too much about catastrophic failure.

What you might try is removing the case and making a close visual
inspection (mark 1 eyeball) of the dipped epoxy solid tantalum
capacitors and other parts in general for signs of overheating like
discoloration, cracking, or surface eruptions. Usually they fail as a
complete short but sometimes they just drop to a low but non-zero
resistance and act as little heaters. A test using your mark 1 nose
might find the problem area.
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[Non-text portions of this message have been removed]

david
 

If I connect both channels to generator with a tee & two 50 ohm cables, channel one is good channel two is bad. can I post a picture of the traces?


From: "Tom Gardner tggzzz@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Wednesday, September 28, 2016 2:29 AM
Subject: Re: [TekScopes] New user with 465 needs help

  For a 100MHz scope (e.g. a 465) and for these purposes you can get away with a
stand 50ohm terminator and a BNC T connector. Of course, a feed-through
terminator is nice to have for faster scopes.

May I suggest that you may benefit from understanding more of the distortions
that can occur with "suboptimal" probing, e.g. a standard *10 probe and 6"
ground lead will resonate at ~100MHz. Such resonances can be very visible when
probing ordinary digital signals.

On 28/09/16 00:38, David davide_us@... [TekScopes] wrote:

I am going to get a 50 ohm feed through terminator and check again
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[Non-text portions of this message have been removed]

 

Take a close look at the volts/div switch shown on either schematic 1
or schematic 2. The x100 high input impedance attenuator is not used
for all of the settings of 0.2V/div and lower so the problem is likely
the x100 attenuator.

These attenuators are socketted into the printed circuit board and
sometimes the socket connections go bad. If this is the problem,
reseating the attenuator module will likely solve it. I had one where
one of the pins did not connect to the hybrid board inside the module
well; removing the cover and touching up the soldering job on the pin
solved that.

You could swap the attenuator modules between channels to see if the
problem follows the bad module.

An interesting test would be to connect your DMM to the BNC input of
the oscilloscope to measure the input resistance on every volts/div
setting with DC coupling selected and the oscilloscope turned on. The
input resistance should always be 1 megohm within about 1%.

On Thu, 29 Sep 2016 00:53:15 +0000 (UTC), you wrote:

Well I'm back to where I started. Checking at 40kHz with 10x probe, square wave, the channels only match at .2V/div setting and below. At .5 V/div channel 1 shows 3 div., top of wave has a curve, is not flat. Channel 2 shows 2.4 div., and top and bottom of wave, is full 90 deg. segment of circle. All the settings above .5 V show channel 2 with the same distortion, and lower amplitude than channel 1. At 1V/div there is 1 div. diff. at 5V/div there is 2.5 div diff. At 1mHz to 4mHz Waveforms look the same, rounded off top and bottom, but channel 2 is 2 div. less amplitude than ch.1. Don't know how to proceed.

Tom Gardner
 

I'm not sure how you would do that with only one tee.

If you connect
siggen-cable-tee/scope-cable-tee/scope/terminator
then that would be suitable for low frequency adjustments, but not for the high-frequency rising/falling edge adjustments. The problem is that the 20pF of the first scope input will put a slight blip on the second scope trace. The blip will be at roughly time = l/(0.7*c), where l is the length of the second cable and c is the speed of light.

It would be best to do two separate measurements, siggen-cable-tee/scope/terminator.

Note that you cannot post photos to this newsgroup, but you can post the URL of where they are stored.

BTW, please delete all the "pretty pictures and lines" at the bottom of a message when replying, since they are responsible for the junk in the reply.

On 29/09/16 02:55, David davide_us@... [TekScopes] wrote:

If I connect both channels to generator with a tee & two 50 ohm cables, channel one is good channel two is bad. can I post a picture of the traces?

From: "Tom Gardner tggzzz@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Wednesday, September 28, 2016 2:29 AM
Subject: Re: [TekScopes] New user with 465 needs help

For a 100MHz scope (e.g. a 465) and for these purposes you can get away with a
stand 50ohm terminator and a BNC T connector. Of course, a feed-through
terminator is nice to have for faster scopes.

May I suggest that you may benefit from understanding more of the distortions
that can occur with "suboptimal" probing, e.g. a standard *10 probe and 6"
ground lead will resonate at ~100MHz. Such resonances can be very visible when
probing ordinary digital signals.

On 28/09/16 00:38, David davide_us@... [TekScopes] wrote:

I am going to get a 50 ohm feed through terminator and check again

david
 

I think you found the problem Dave, I swapped the x100 attenuators and the symptoms are on channel 1 now.Is it possible that it just needs adjusted? Probably not the original part because Channel 1 part is older Part no. 307-1014-01, and bad channel 2 is newer Part no. 307-1014-02.


From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Wednesday, September 28, 2016 11:21 PM
Subject: Re: [TekScopes] New user with 465 needs help

  Take a close look at the volts/div switch shown on either schematic 1
or schematic 2. The x100 high input impedance attenuator is not used
for all of the settings of 0.2V/div and lower so the problem is likely
the x100 attenuator.

These attenuators are socketted into the printed circuit board and
sometimes the socket connections go bad. If this is the problem,
reseating the attenuator module will likely solve it. I had one where
one of the pins did not connect to the hybrid board inside the module
well; removing the cover and touching up the soldering job on the pin
solved that.

You could swap the attenuator modules between channels to see if the
problem follows the bad module.

An interesting test would be to connect your DMM to the BNC input of
the oscilloscope to measure the input resistance on every volts/div
setting with DC coupling selected and the oscilloscope turned on. The
input resistance should always be 1 megohm within about 1%.

On Thu, 29 Sep 2016 00:53:15 +0000 (UTC), you wrote:

Well I'm back to where I started. Checking at 40kHz with 10x probe, square wave, the channels only match at .2V/div setting and below. At .5 V/div channel 1 shows 3 div., top of wave has a curve, is not flat. Channel 2 shows 2.4 div., and top and bottom of wave, is full 90 deg. segment of circle. All the settings above .5 V show channel 2 with the same distortion, and lower amplitude than channel 1. At 1V/div there is 1 div. diff. at 5V/div there is 2.5 div diff. At 1mHz to 4mHz Waveforms look the same, rounded off top and bottom, but channel 2 is 2 div. less amplitude than ch.1. Don't know how to proceed.
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[Non-text portions of this message have been removed]

david
 

I didn't ask you, are those part numbers are interchangeable? I can get part number 307-1014-00, will this part work?


From: "David davide_us@... [TekScopes]" <TekScopes@...>
To: "TekScopes@..." <TekScopes@...>
Sent: Thursday, September 29, 2016 6:10 PM
Subject: Re: [TekScopes] New user with 465 needs help

  I think you found the problem Dave, I swapped the x100 attenuators and the symptoms are on channel 1 now.Is it possible that it just needs adjusted? Probably not the original part because Channel 1 part is older Part no. 307-1014-01, and bad channel 2 is newer Part no. 307-1014-02.

From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Wednesday, September 28, 2016 11:21 PM
Subject: Re: [TekScopes] New user with 465 needs help

  Take a close look at the volts/div switch shown on either schematic 1
or schematic 2. The x100 high input impedance attenuator is not used
for all of the settings of 0.2V/div and lower so the problem is likely
the x100 attenuator.

These attenuators are socketted into the printed circuit board and
sometimes the socket connections go bad. If this is the problem,
reseating the attenuator module will likely solve it. I had one where
one of the pins did not connect to the hybrid board inside the module
well; removing the cover and touching up the soldering job on the pin
solved that.

You could swap the attenuator modules between channels to see if the
problem follows the bad module.

An interesting test would be to connect your DMM to the BNC input of
the oscilloscope to measure the input resistance on every volts/div
setting with DC coupling selected and the oscilloscope turned on. The
input resistance should always be 1 megohm within about 1%.

On Thu, 29 Sep 2016 00:53:15 +0000 (UTC), you wrote:

Well I'm back to where I started. Checking at 40kHz with 10x probe, square wave, the channels only match at .2V/div setting and below. At .5 V/div channel 1 shows 3 div., top of wave has a curve, is not flat. Channel 2 shows 2.4 div., and top and bottom of wave, is full 90 deg. segment of circle. All the settings above .5 V show channel 2 with the same distortion, and lower amplitude than channel 1. At 1V/div there is 1 div. diff. at 5V/div there is 2.5 div diff. At 1mHz to 4mHz Waveforms look the same, rounded off top and bottom, but channel 2 is 2 div. less amplitude than ch.1. Don't know how to proceed.
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[Non-text portions of this message have been removed]

 

The adjustments are for input capacitance and compensation. Input
capacitance is adjusted using a normalizer or x10 probe and
compensation is adjusted using a 50 ohm termination at the BNC. The
compensation adjustment affects the input capacitance adjustment a
little bit.

If you want to make sure, use a 1 kHz square wave test signal into the
50 ohm termination and look to see if it square without roll off or
peaking of the leading edge when the x100 attenuator is selected by
the volts/div setting.

The rather nebulous procedure for this calibration starts on page 6-18
of the service manual. I think C10/C60 is the adjustment which
matters in this case.

The plastic top can be popped off of the attenuator module for visual
inspection which may reveal the problem.

On Thu, 29 Sep 2016 22:10:02 +0000 (UTC), you wrote:

I think you found the problem Dave, I swapped the x100 attenuators and the symptoms are on channel 1 now.Is it possible that it just needs adjusted? Probably not the original part because Channel 1 part is older Part no. 307-1014-01, and bad channel 2 is newer Part no. 307-1014-02.

From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Wednesday, September 28, 2016 11:21 PM
Subject: Re: [TekScopes] New user with 465 needs help

  Take a close look at the volts/div switch shown on either schematic 1
or schematic 2. The x100 high input impedance attenuator is not used
for all of the settings of 0.2V/div and lower so the problem is likely
the x100 attenuator.

These attenuators are socketted into the printed circuit board and
sometimes the socket connections go bad. If this is the problem,
reseating the attenuator module will likely solve it. I had one where
one of the pins did not connect to the hybrid board inside the module
well; removing the cover and touching up the soldering job on the pin
solved that.

You could swap the attenuator modules between channels to see if the
problem follows the bad module.

An interesting test would be to connect your DMM to the BNC input of
the oscilloscope to measure the input resistance on every volts/div
setting with DC coupling selected and the oscilloscope turned on. The
input resistance should always be 1 megohm within about 1%.

 

I think they are interchangeable. Tektronix used these in a lot of
different products.

If they are different, then maybe whoever swapped it did not adjust
it.

On Thu, 29 Sep 2016 22:36:02 +0000 (UTC), you wrote:

I didn't ask you, are those part numbers are interchangeable? I can get part number 307-1014-00, will this part work?

From: "David davide_us@... [TekScopes]" <TekScopes@...>
To: "TekScopes@..." <TekScopes@...>
Sent: Thursday, September 29, 2016 6:10 PM
Subject: Re: [TekScopes] New user with 465 needs help

  I think you found the problem Dave, I swapped the x100 attenuators and the symptoms are on channel 1 now.Is it possible that it just needs adjusted? Probably not the original part because Channel 1 part is older Part no. 307-1014-01, and bad channel 2 is newer Part no. 307-1014-02.

Tom Jobe <tomjobe@...>
 

To add on to what David Hess has been trying to explain..
I doubt the X100 attenuator's part number dash version matters.
If it is not a simple attenuator adjustment problem, then take the
attenuator apart.
The top of the attenuator comes off by pushing in on the little white
hooks in the two holes on either side of the attenuator body.
Inside there are six pins that are soldered to a small printed circuit
board. The solder connections to the six pins often break, and even
though they were soldered with some odd type of solder, you can often
repair them with normal lead-tin solder and good soldering equipment if
you clean the immediate area around the broken solder joint before you
start your solder repair.
tom jobe...

On 9/29/2016 3:10 PM, David davide_us@... [TekScopes] wrote:

I think you found the problem Dave, I swapped the x100 attenuators and
the symptoms are on channel 1 now.Is it possible that it just needs
adjusted? Probably not the original part because Channel 1 part is
older Part no. 307-1014-01, and bad channel 2 is newer Part no.
307-1014-02.

From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Wednesday, September 28, 2016 11:21 PM
Subject: Re: [TekScopes] New user with 465 needs help

Take a close look at the volts/div switch shown on either schematic 1
or schematic 2. The x100 high input impedance attenuator is not used
for all of the settings of 0.2V/div and lower so the problem is likely
the x100 attenuator.

These attenuators are socketted into the printed circuit board and
sometimes the socket connections go bad. If this is the problem,
reseating the attenuator module will likely solve it. I had one where
one of the pins did not connect to the hybrid board inside the module
well; removing the cover and touching up the soldering job on the pin
solved that.

You could swap the attenuator modules between channels to see if the
problem follows the bad module.

An interesting test would be to connect your DMM to the BNC input of
the oscilloscope to measure the input resistance on every volts/div
setting with DC coupling selected and the oscilloscope turned on. The
input resistance should always be 1 megohm within about 1%.

On Thu, 29 Sep 2016 00:53:15 +0000 (UTC), you wrote:

Well I'm back to where I started. Checking at 40kHz with 10x probe,
square wave, the channels only match at .2V/div setting and below. At
.5 V/div channel 1 shows 3 div., top of wave has a curve, is not flat.
Channel 2 shows 2.4 div., and top and bottom of wave, is full 90 deg.
segment of circle. All the settings above .5 V show channel 2 with the
same distortion, and lower amplitude than channel 1. At 1V/div there
is 1 div. diff. at 5V/div there is 2.5 div diff. At 1mHz to 4mHz
Waveforms look the same, rounded off top and bottom, but channel 2 is
2 div. less amplitude than ch.1. Don't know how to proceed.
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[Non-text portions of this message have been removed]



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

david
 

I tested the inputs with ohm meter. Channel with 307-1014-01 attenuator is 1M ohm all voltage settings. Channel with suspect 307-1014-02 attenuator is 1M ohm thru .2V/div, all higher voltage settings show .993M ohm. 7K ohm difference. Doesn't matter which channel it is in, reads the same. The 307-1014-02 is correct part in part list, 


From: "David @DWH [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Thursday, September 29, 2016 7:15 PM
Subject: Re: [TekScopes] New user with 465 needs help

  I think they are interchangeable. Tektronix used these in a lot of
different products.

If they are different, then maybe whoever swapped it did not adjust
it.





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

 

A change from 1.000 megohms to 0.993 megohms is not significant so
maybe the input capacitance and compensation just needs to be
adjusted.

On Fri, 30 Sep 2016 00:06:07 +0000 (UTC), you wrote:

I tested the inputs with ohm meter. Channel with 307-1014-01 attenuator is 1M ohm all voltage settings. Channel with suspect 307-1014-02 attenuator is 1M ohm thru .2V/div, all higher voltage settings show .993M ohm. 7K ohm difference. Doesn't matter which channel it is in, reads the same. The 307-1014-02 is correct part in part list,