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Hey guys. I have done a lot of work to this 465. I had initially planned on selling it to help me buy some plugins for my 7633. I decided I don't want to sell it and am keeping it. Today I checked its rise time with a pg506 fast rise. Both channel 1 and 2 closely resemble each other and they are not close to right. Before I start trying to calibrate this thing, does it look like there is some type of component issue left to fix? I am thinking since both channels are so alike there is something wrong besides just out of calibration. Thanks guys. here are some pictures /g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0 /g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
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On Sun, 17 Jun 2018 18:47:37 -0700, you wrote: Hey guys. I have done a lot of work to this 465. I had initially planned on selling it to help me buy some plugins for my 7633. I decided I don't want to sell it and am keeping it. Today I checked its rise time with a pg506 fast rise. Both channel 1 and 2 closely resemble each other and they are not close to right. Before I start trying to calibrate this thing, does it look like there is some type of component issue left to fix? I am thinking since both channels are so alike there is something wrong besides just out of calibration. Thanks guys. This may not be exactly what you think. Rise time is measured from 10% to 90%. I'd have to look at the manual for that scope, but I remember that the dotted lines on the graticule are supposed to measure the 10% to 90% parts of the waveform. I think one problem is that you have too little vertical gain at the moment. Bear in mind that the risetime also varies with the vertical gain control. I'd check the manual and see exactly how you are supposed to measure risetime before thinking that the risetime is bad. Harvey
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
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On Sun, Jun 17, 2018 at 07:03 pm, Harvey White wrote:
On Sun, 17 Jun 2018 18:47:37 -0700, you wrote:
Hey guys. I have done a lot of work to this 465. I had initially planned on selling it to help me buy some plugins for my 7633. I decided I don't want to
sell it and am keeping it. Today I checked its rise time with a pg506 fast
rise. Both channel 1 and 2 closely resemble each other and they are not close
to right. Before I start trying to calibrate this thing, does it look like
there is some type of component issue left to fix? I am thinking since both
channels are so alike there is something wrong besides just out of
calibration. Thanks guys.
This may not be exactly what you think. Rise time is measured from
10% to 90%. I'd have to look at the manual for that scope, but I
remember that the dotted lines on the graticule are supposed to
measure the 10% to 90% parts of the waveform. I think one problem is
that you have too little vertical gain at the moment. Bear in mind
that the risetime also varies with the vertical gain control.
I'd check the manual and see exactly how you are supposed to measure
risetime before thinking that the risetime is bad.
Harvey
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
In the manual it says to set .05us and remove and add attenuators to keep the 5 divisions and to check for 3.5ns rise time. I used a 50ohm through termination with .2V/div. with the pg506 all most maxed out. I did set 10x mag because I dont know how to see 3.5ns while setting the time at .05us/50ns the trace is wider than 3.5ns. Duplicating the exact setup on my 468 shows the correct 3.5ns rise time without that giant round shoulder. Thanks for your help :)
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You are looking at the waveform with a scope probe that presents a 10 meg ohm load to the pulse generator. What you need to do is use a 50 ohm cable to go from the generator to the scope input and include a 50 ohm through termination right at the scope. A real simple solution would be to use a BNC T with the center loaded with a 49.9 ohm resistor. Or just look for a 50 ohm through termination on ebay.
Regards
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Show quoted text
----- Original Message ----- From: "lop pol via Groups.Io" <the_infinite_penguin@...> To: < [email protected]> Sent: Sunday, June 17, 2018 9:47 PM Subject: [TekScopes] 465 bad rise time Hey guys. I have done a lot of work to this 465. I had initially planned on selling it to help me buy some plugins for my 7633. I decided I don't want to sell it and am keeping it. Today I checked its rise time with a pg506 fast rise. Both channel 1 and 2 closely resemble each other and they are not close to right. Before I start trying to calibrate this thing, does it look like there is some type of component issue left to fix? I am thinking since both channels are so alike there is something wrong besides just out of calibration. Thanks guys. here are some pictures /g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0 /g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
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toggle quoted message
Show quoted text
On Sun, Jun 17, 2018 at 08:50 pm, tmillermdems wrote:
You are looking at the waveform with a scope probe that presents a 10 meg
ohm load to the pulse generator. What you need to do is use a 50 ohm cable
to go from the generator to the scope input and include a 50 ohm through
termination right at the scope. A real simple solution would be to use a BNC
T with the center loaded with a 49.9 ohm resistor. Or just look for a 50 ohm
through termination on ebay.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Sunday, June 17, 2018 9:47 PM
Subject: [TekScopes] 465 bad rise time
Hey guys. I have done a lot of work to this 465. I had initially planned on
selling it to help me buy some plugins for my 7633. I decided I don't want
to sell it and am keeping it. Today I checked its rise time with a pg506
fast rise. Both channel 1 and 2 closely resemble each other and they are not
close to right. Before I start trying to calibrate this thing, does it look
like there is some type of component issue left to fix? I am thinking since
both channels are so alike there is something wrong besides just out of
calibration. Thanks guys.
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
|
Ok, it looked like a probe at first. What is the H sweep rate set to? Can't see it in the pictures.
Looks like 1 1/4 divisions on the horizontal 10-90% points.
Regards
toggle quoted message
Show quoted text
----- Original Message ----- From: "lop pol via Groups.Io" <the_infinite_penguin@...> To: < [email protected]> Sent: Monday, June 18, 2018 12:02 AM Subject: Re: [TekScopes] 465 bad rise time Im using a 50ohm cable with a 50ohm through terminator. /g/TekScopes/photo/59361/2?p=Name,,,20,1,0,0 On Sun, Jun 17, 2018 at 08:50 pm, tmillermdems wrote:
You are looking at the waveform with a scope probe that presents a 10 meg
ohm load to the pulse generator. What you need to do is use a 50 ohm cable
to go from the generator to the scope input and include a 50 ohm through
termination right at the scope. A real simple solution would be to use a BNC
T with the center loaded with a 49.9 ohm resistor. Or just look for a 50 ohm
through termination on ebay.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Sunday, June 17, 2018 9:47 PM
Subject: [TekScopes] 465 bad rise time
Hey guys. I have done a lot of work to this 465. I had initially planned on
selling it to help me buy some plugins for my 7633. I decided I don't want
to sell it and am keeping it. Today I checked its rise time with a pg506
fast rise. Both channel 1 and 2 closely resemble each other and they are not
close to right. Before I start trying to calibrate this thing, does it look
like there is some type of component issue left to fix? I am thinking since
both channels are so alike there is something wrong besides just out of
calibration. Thanks guys.
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
|
Time div is set to .05us but I have 10x mag on so that should be 5ns.
toggle quoted message
Show quoted text
On Sun, Jun 17, 2018 at 09:10 pm, tmillermdems wrote:
Ok, it looked like a probe at first. What is the H sweep rate set to? Can't
see it in the pictures.
Looks like 1 1/4 divisions on the horizontal 10-90% points.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Monday, June 18, 2018 12:02 AM
Subject: Re: [TekScopes] 465 bad rise time
Im using a 50ohm cable with a 50ohm through terminator.
/g/TekScopes/photo/59361/2?p=Name,,,20,1,0,0
On Sun, Jun 17, 2018 at 08:50 pm, tmillermdems wrote:
You are looking at the waveform with a scope probe that presents a 10 meg
ohm load to the pulse generator. What you need to do is use a 50 ohm cable
to go from the generator to the scope input and include a 50 ohm through
termination right at the scope. A real simple solution would be to use a
BNC
T with the center loaded with a 49.9 ohm resistor. Or just look for a 50
ohm
through termination on ebay.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Sunday, June 17, 2018 9:47 PM
Subject: [TekScopes] 465 bad rise time
Hey guys. I have done a lot of work to this 465. I had initially planned
on
selling it to help me buy some plugins for my 7633. I decided I don't want
to sell it and am keeping it. Today I checked its rise time with a pg506
fast rise. Both channel 1 and 2 closely resemble each other and they are
not
close to right. Before I start trying to calibrate this thing, does it
look
like there is some type of component issue left to fix? I am thinking
since
both channels are so alike there is something wrong besides just out of
calibration. Thanks guys.
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
|
So BW = 0.35/risetime in seconds or 0.35/0.000000006 = ~~60 MHz.
The 465 should go around 100 MHz bandwidth. Around 3.5 ns.
Is the bandwidth limit turned on ( maybe a fault with the switching? ).
Do you have any other scope with a higher bandwidth available? Some way to verify the setup.
toggle quoted message
Show quoted text
----- Original Message ----- From: "lop pol via Groups.Io" <the_infinite_penguin@...> To: < [email protected]> Sent: Monday, June 18, 2018 12:22 AM Subject: Re: [TekScopes] 465 bad rise time Time div is set to .05us but I have 10x mag on so that should be 5ns. On Sun, Jun 17, 2018 at 09:10 pm, tmillermdems wrote:
Ok, it looked like a probe at first. What is the H sweep rate set to? Can't
see it in the pictures.
Looks like 1 1/4 divisions on the horizontal 10-90% points.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Monday, June 18, 2018 12:02 AM
Subject: Re: [TekScopes] 465 bad rise time
Im using a 50ohm cable with a 50ohm through terminator.
/g/TekScopes/photo/59361/2?p=Name,,,20,1,0,0
On Sun, Jun 17, 2018 at 08:50 pm, tmillermdems wrote:
You are looking at the waveform with a scope probe that presents a 10 meg
ohm load to the pulse generator. What you need to do is use a 50 ohm cable
to go from the generator to the scope input and include a 50 ohm through
termination right at the scope. A real simple solution would be to use a
BNC
T with the center loaded with a 49.9 ohm resistor. Or just look for a 50
ohm
through termination on ebay.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Sunday, June 17, 2018 9:47 PM
Subject: [TekScopes] 465 bad rise time
Hey guys. I have done a lot of work to this 465. I had initially planned
on
selling it to help me buy some plugins for my 7633. I decided I don't want
to sell it and am keeping it. Today I checked its rise time with a pg506
fast rise. Both channel 1 and 2 closely resemble each other and they are
not
close to right. Before I start trying to calibrate this thing, does it
look
like there is some type of component issue left to fix? I am thinking
since
both channels are so alike there is something wrong besides just out of
calibration. Thanks guys.
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
|
With curves like this /g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0 I wouldn't even bother to calculate a rise time. Obviously the main problem is roll-off. I would search the manual for Adjustments which influence that nanoseconds part of the curve and try these first.
On Sun, Jun 17, 2018 at 09:59 pm, tmillermdems wrote:
So BW = 0.35/risetime in seconds or 0.35/0.000000006 = ~~60 MHz.
The 465 should go around 100 MHz bandwidth. Around 3.5 ns.
Is the bandwidth limit turned on ( maybe a fault with the switching? ).
Do you have any other scope with a higher bandwidth available? Some way to
verify the setup.
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Monday, June 18, 2018 12:22 AM
Subject: Re: [TekScopes] 465 bad rise time
Time div is set to .05us but I have 10x mag on so that should be 5ns.
On Sun, Jun 17, 2018 at 09:10 pm, tmillermdems wrote:
Ok, it looked like a probe at first. What is the H sweep rate set to?
Can't
see it in the pictures.
Looks like 1 1/4 divisions on the horizontal 10-90% points.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Monday, June 18, 2018 12:02 AM
Subject: Re: [TekScopes] 465 bad rise time
Im using a 50ohm cable with a 50ohm through terminator.
/g/TekScopes/photo/59361/2?p=Name,,,20,1,0,0
On Sun, Jun 17, 2018 at 08:50 pm, tmillermdems wrote:
You are looking at the waveform with a scope probe that presents a 10
meg
ohm load to the pulse generator. What you need to do is use a 50 ohm
cable
to go from the generator to the scope input and include a 50 ohm through
termination right at the scope. A real simple solution would be to use a
BNC
T with the center loaded with a 49.9 ohm resistor. Or just look for a 50
ohm
through termination on ebay.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Sunday, June 17, 2018 9:47 PM
Subject: [TekScopes] 465 bad rise time
Hey guys. I have done a lot of work to this 465. I had initially planned
on
selling it to help me buy some plugins for my 7633. I decided I don't
want
to sell it and am keeping it. Today I checked its rise time with a pg506
fast rise. Both channel 1 and 2 closely resemble each other and they are
not
close to right. Before I start trying to calibrate this thing, does it
look
like there is some type of component issue left to fix? I am thinking
since
both channels are so alike there is something wrong besides just out of
calibration. Thanks guys.
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
|
Is the bandwidth limit turned on ( maybe a fault with the switching? )
The BW limit switch is off. Turning it on increases the rise time and smoothed the trace like I would expect. Do you have any other scope with a higher bandwidth available? Some way to
verify the setup. Yes but i checked the setup with my 468 (100 mhz) and the rise time was the correct 3.5ns On Mon, Jun 18, 2018 at 12:34 am, Albert Otten wrote:
With curves like this
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0 I wouldn't even
bother to calculate a rise time. Obviously the main problem is roll-off. I
would search the manual for Adjustments which influence that nanoseconds part
of the curve and try these first.
Ok. I will start turning screws. I just wanted to get opinions on whether this could possibly be a problem with a bad component prior to messing with the calibration. I would hate to have a bad transistor or capacitor causing the bad rise time and start turning the adjustments and mess up something that was actually already set correctly. So BW = 0.35/risetime in seconds or 0.35/0.000000006 = ~~60 MHz.
The 465 should go around 100 MHz bandwidth. Around 3.5 ns.
.
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Monday, June 18, 2018 12:22 AM
Subject: Re: [TekScopes] 465 bad rise time
Time div is set to .05us but I have 10x mag on so that should be 5ns.
On Sun, Jun 17, 2018 at 09:10 pm, tmillermdems wrote:
Ok, it looked like a probe at first. What is the H sweep rate set to?
Can't
see it in the pictures.
Looks like 1 1/4 divisions on the horizontal 10-90% points.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Monday, June 18, 2018 12:02 AM
Subject: Re: [TekScopes] 465 bad rise time
Im using a 50ohm cable with a 50ohm through terminator.
/g/TekScopes/photo/59361/2?p=Name,,,20,1,0,0
On Sun, Jun 17, 2018 at 08:50 pm, tmillermdems wrote:
You are looking at the waveform with a scope probe that presents a 10
meg
ohm load to the pulse generator. What you need to do is use a 50 ohm
cable
to go from the generator to the scope input and include a 50 ohm through
termination right at the scope. A real simple solution would be to use a
BNC
T with the center loaded with a 49.9 ohm resistor. Or just look for a 50
ohm
through termination on ebay.
Regards
----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin@...>
To: <[email protected]>
Sent: Sunday, June 17, 2018 9:47 PM
Subject: [TekScopes] 465 bad rise time
Hey guys. I have done a lot of work to this 465. I had initially planned
on
selling it to help me buy some plugins for my 7633. I decided I don't
want
to sell it and am keeping it. Today I checked its rise time with a pg506
fast rise. Both channel 1 and 2 closely resemble each other and they are
not
close to right. Before I start trying to calibrate this thing, does it
look
like there is some type of component issue left to fix? I am thinking
since
both channels are so alike there is something wrong besides just out of
calibration. Thanks guys.
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
|
On Mon, Jun 18, 2018 at 04:23 am, lop pol wrote:
I will start turning screws. I just wanted to get opinions on whether this
could possibly be a problem with a bad component prior to messing with the
calibration.
Before you start turning screws: 1. It is not uncommon for the variable caps to become open. I've had that happen to some in the vertical (output) amplifier. I've seen both the rotor not moving *and* the connection to the stator opening up. When screwing, check those first by watching their influence. 2. Look at the flatness of the square wave at lower frequencies (1 kHz, 10 kHz and up). I've seen an increase of the impedance in the differential circuits out of the delay line causing huge distortions, not just slow edges, by high-drifting low-value R's. Now that I've become involved, I have to ask a stupid(?) question: You *are* using the right i.e. fast edges of the PG506, are you? The left-hand BNC has a fast *fall* time, the middle BNC has a fast *rise* time. Raymond
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You have the proper fast rise generator to perform an adjustment. The risk in my opinion is that you destroy a stuck trimcap or trimpot.
You might first verify DC levels in the output amplifier stages and perhaps symmetry in the push-pull signals. Often some stages are common-base current driven which makes it more difficult to check signals.
Unlike some other manuals the 465 manuals do not tell which part of the curve is affected by each adjustment.
Which version output amplifier is in your 465, discrete or IC? It seems you use the pre-B250000 manual because of what you said about the 10X magnifier. The B250000-up manual clearly mentions the 10X mag. That manual also shows both versions output amplifier.
toggle quoted message
Show quoted text
On Mon, Jun 18, 2018 at 04:23 am, lop pol wrote:
On Mon, Jun 18, 2018 at 12:34 am, Albert Otten wrote:
With curves like this
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0 I wouldn't
even bother to calculate a rise time. Obviously the main problem is roll-off. I
would search the manual for Adjustments which influence that nanoseconds
part of the curve and try these first.
Ok. I will start turning screws. I just wanted to get opinions on whether this
could possibly be a problem with a bad component prior to messing with the
calibration. I would hate to have a bad transistor or capacitor causing the
bad rise time and start turning the adjustments and mess up something that was
actually already set correctly.
|
On Mon, Jun 18, 2018 at 04:41 am, Raymond Domp Frank wrote:
On Mon, Jun 18, 2018 at 04:23 am, lop pol wrote:
I will start turning screws. I just wanted to get opinions on whether this
could possibly be a problem with a bad component prior to messing with the
calibration.
Before you start turning screws:
1. It is not uncommon for the variable caps to become open. I've had that
happen to some in the vertical (output) amplifier. I've seen both the rotor
not moving *and* the connection to the stator opening up. When screwing, check
those first by watching their influence.
2. Look at the flatness of the square wave at lower frequencies (1 kHz, 10 kHz
and up). I've seen an increase of the impedance in the differential circuits
out of the delay line causing huge distortions, not just slow edges, by
high-drifting low-value R's.
Now that I've become involved, I have to ask a stupid(?) question: You *are*
using the right i.e. fast edges of the PG506, are you? The left-hand BNC has a
fast *fall* time, the middle BNC has a fast *rise* time.
Raymond
Yes I'm using the correct output. The rise time reminded me of my 7a26 that had bad var capacitors, but that only affected one channel. Seeing that are both channels are essentially the same just seems weird to me.
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On Mon, Jun 18, 2018 at 05:06 am, lop pol wrote:
Seeing that are both channels are essentially the same just seems weird to me.
The vertical output Amp and some other parts, like parts of the channel switch, are common. Raymond
|
|
|
Sorry Raymond, again I missed you message of a few minutes ago!
BTW I sold my one and only 465 some time ago, so I can't help with doing measurements.
Albert
|
What is the source of the signal being displayed ?
What kind of probe is being used ?Is it compensated ??Is the probe ground lead connected ?
Do yourself a favor & lose the probe.Connect to a decent signal source, via coax, using a 50 ohm termination at the scope end.
HankC, Boston
|
Im using a 50ohm cable a 50ohm through termination and a pg506 fast rise pulse.
toggle quoted message
Show quoted text
On Mon, Jun 18, 2018 at 08:31 am, HankC, Boston, WA1HOS wrote:
What is the source of the signal being displayed ?
What kind of probe is being used ?Is it compensated ??Is the probe ground lead
connected ?
Do yourself a favor & lose the probe.Connect to a decent signal source, via
coax, using a 50 ohm termination at the scope end.
HankC, Boston
|
I'm calling it close enough. The previous owner had turned every var/cap/resistor available and he may sneak into your lab and turn your too. Lock your doors. /g/TekScopes/photo/59361/3?p=Name,,,20,1,0,0 Hey guys. I have done a lot of work to this 465. I had initially planned on selling it to help me buy some plugins for my 7633. I decided I don't want to sell it and am keeping it. Today I checked its rise time with a pg506 fast rise. Both channel 1 and 2 closely resemble each other and they are not close to right. Before I start trying to calibrate this thing, does it look like there is some type of component issue left to fix? I am thinking since both channels are so alike there is something wrong besides just out of calibration. Raymond Domp Frank Jun 18 #148963
On Mon, Jun 18, 2018 at 05:06 am, lop pol wrote:
Seeing that are both channels are essentially the same just seems weird to me.
The vertical output Amp and some other parts, like parts of the channel switch, are common.
Raymond
You have the proper fast rise generator to perform an adjustment. The risk in my opinion is that you destroy a stuck trimcap or trimpot.
You might first verify DC levels in the output amplifier stages and perhaps symmetry in the push-pull signals. Often some stages are common-base current driven which makes it more difficult to check signals.
Unlike some other manuals the 465 manuals do not tell which part of the curve is affected by each adjustment.
Which version output amplifier is in your 465, discrete or IC? It seems you use the pre-B250000 manual because of what you said about the 10X magnifier. The B250000-up manual clearly mentions the 10X mag. That manual also shows both versions output amplifier.
|
Hello lop pol,
I've followed up this topic from the start, without having actually jumped in, hoping since the beginning that someone would ask or make remarks about two or three important things (to check, or to be aware of).
1. That's a question... What type of Vertical Output board does your 465 have. the one discrete or the one with the custom Tek IC?
It's important because the High Freq. compensation networks are different from one type of board to the other and since your problem manifests in both channels, there's a great likelihood the problem is located on the Vertical Output Amplifier board, instead of on the pre-amplifier. Without that information is difficult to advise further.
2. If your vertical amplifier is of the "Teck IC" kind, look also to the BIAS trimpot. If the wiper is open, the amplifier may be operating on the wrong bias point and that is supposed to impact the high-frequency performance.
Since the procedure for calibrating the bias calls for applying a 100Mhz signal and adjusting the bias for the highest p-p display, from there we deduct it has a marked effect on the low nanosecond time constant, which is exactly where your issue lies.
3. Besides what Raymond already mentioned, that is not uncommon for some of those trimmer caps fail open (I had 3 of those failed on my 464), I want to bring to your attention that ALL the trimpots that are used on the H.F. compensation networks are connected as "rheostats" so, a false contact or open wiper will make any of them appear open, or in the best case, the full trimpot's resistance, which will be just as bad for the step response.
Since many of them are in series with trimmer caps, it's easy to check them in circuit, without needing to lift any leg, or remove any component.
Last but not least, despite your problem clearly doesn't seem to be on the pre-amplifiers, when you find out the culprit and eventually replace one faulty trimmer cap or faulty trimmer resistor, you will eventually need to go through the Vertical High Frequency step response calibration, and for that, it's important that you follow the procedure, and from your description, I think you're already doing wrong...
While choosing for the right input level / input attenuator (pass-through) and vertical attenuator settings, it's important to do all the High-Frequency calibration with the oscilloscope set to the most sensitive setting... i.e.: 5mV/div (not 10mV, not 100mV... and not 200mV/div).
In other words, you need to source 25mVpp to the oscilloscope's input (for a 5 division display).
This is what will assure you that none of the high impedance input attenuators are upsetting the subtle high frequency adjustments and artifacts.
While - in theory - the high-impedance input attenuators shouldn't degrade the step response of the osciloscope, they're not perfect and they do cause some minor disturbances and aberrations to the step response (and they can also be misadjusted, something that you will only correct at a later stage) so, to make a "clean" H.F. calibration, you need to make sure you got them (the high impedance input attenuators) out of the way.
The only compromise to that rule is the input probe itself... If you intend to use the oscilloscope with a particular probe (let's say, a 10:1), then you need to connect that probe to the input, use the scope set to 5mV/div, and apply, accordingly, a 250mVpp signal to the probe (if it's a 10:1 probe). This will assure you will compensate in the scope, for the probe's H.F. inaccuracies or artifacts.
Yet on this topic, you need to be sure to "source" that signal (regardless if directly to the input or through your preferred probe), from a low impedance source (50Ohm).
The latter is important because you don't want the frequency response of the incoming signal to be affected by variations caused by the 'scope's input capacitance, or your probe's input capacitance.
The lower the impedance of the source signal, the less the input capacitance will matter and, of course, you will also want to assure the interconnect cable is properly terminated.
Good luck with that,
Krgrds,
Fabio
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On Sun, Jun 17, 2018 at 06:47 pm, lop pol wrote:
Hey guys. I have done a lot of work to this 465. I had initially planned on
selling it to help me buy some plugins for my 7633. I decided I don't want to
sell it and am keeping it. Today I checked its rise time with a pg506 fast
rise. Both channel 1 and 2 closely resemble each other and they are not close
to right. Before I start trying to calibrate this thing, does it look like
there is some type of component issue left to fix? I am thinking since both
channels are so alike there is something wrong besides just out of
calibration. Thanks guys.
here are some pictures
/g/TekScopes/photo/59361/0?p=Name,,,20,1,0,0
/g/TekScopes/photo/59361/1?p=Name,,,20,1,0,0
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Raymond Domp Frank
Fabio Trevisan