Type CA Channel B Gain Adj Problem


Cliff White <w5cnw@...>
 

I just finished repairing a Type CA plugin. Everything seems to have calibrated just fine, with the exception of the channel B gain. It won't go low enough. For example, if I apply a .1 volt P-P signal, at .05 volts/div, the lowest the gain will adjust to is about 2.3 divs. It will go higher, but not any lower. Channel A adjusts perfectly. All other adjustments on both channels work fine. Does anyone have any ideas as to how I can fix this?


--
Respectfully,
Cliff White, W5CNW
w5cnw@...


Don Black <donald_black@...>
 

Perhaps a plate resistor gone high, likely to increase gain but also effect frequency response.

Don Black.

On 30-Apr-13 12:07 PM, Cliff White wrote:
 

I just finished repairing a Type CA plugin. Everything seems to have calibrated just fine, with the exception of the channel B gain. It won't go low enough. For example, if I apply a .1 volt P-P signal, at .05 volts/div, the lowest the gain will adjust to is about 2.3 divs. It will go higher, but not any lower. Channel A adjusts perfectly. All other adjustments on both channels work fine. Does anyone have any ideas as to how I can fix this?


--
Respectfully,
Cliff White, W5CNW
w5cnw@...


 

First I would check the values of the resistors and potentiometers in
the cathode network for V4334 and V4354 and the voltage at the cathode
of V3393B. Then I would check the values of the resistors in the
cathode network for V4364 and V4374.

If none of the above turned up anything, then I would swap the matched
pairs of tubes between channel A and channel B to see if the problem
moves to channel A.

On Mon, 29 Apr 2013 21:07:29 -0500, Cliff White <w5cnw@arrl.net>
wrote:

I just finished repairing a Type CA plugin. Everything seems to have
calibrated just fine, with the exception of the channel B gain. It won't
go low enough. For example, if I apply a .1 volt P-P signal, at .05
volts/div, the lowest the gain will adjust to is about 2.3 divs. It will
go higher, but not any lower. Channel A adjusts perfectly. All other
adjustments on both channels work fine. Does anyone have any ideas as to
how I can fix this?


PA4TIM
 

Knob mounted wrong ? Or is it just in one position a problem.

Fred PA4TIM

Op 30 apr. 2013 om 04:07 heeft Cliff White <w5cnw@...> het volgende geschreven:

 

I just finished repairing a Type CA plugin. Everything seems to have calibrated just fine, with the exception of the channel B gain. It won't go low enough. For example, if I apply a .1 volt P-P signal, at .05 volts/div, the lowest the gain will adjust to is about 2.3 divs. It will go higher, but not any lower. Channel A adjusts perfectly. All other adjustments on both channels work fine. Does anyone have any ideas as to how I can fix this?


--
Respectfully,
Cliff White, W5CNW
w5cnw@...


Cliff White <w5cnw@...>
 

All resistor values match between the two channels. R4337 and R4357 are 2.75K, instead of the 5.6K marked on the schematic, but the corresponding resistors on channel A are also 2.75K. The voltage at the cathode of V3393B is 39.8 volts, while the voltage on the cathode of V3393A is 29.8 volts.


Respectfully,
Cliff White, W5CNW
w5cnw@...

On 04/29/2013 09:43 PM, David wrote:
 

First I would check the values of the resistors and potentiometers in
the cathode network for V4334 and V4354 and the voltage at the cathode
of V3393B. Then I would check the values of the resistors in the
cathode network for V4364 and V4374.

If none of the above turned up anything, then I would swap the matched
pairs of tubes between channel A and channel B to see if the problem
moves to channel A.

On Mon, 29 Apr 2013 21:07:29 -0500, Cliff White <w5cnw@...>
wrote:

>I just finished repairing a Type CA plugin. Everything seems to have
>calibrated just fine, with the exception of the channel B gain. It won't
>go low enough. For example, if I apply a .1 volt P-P signal, at .05
>volts/div, the lowest the gain will adjust to is about 2.3 divs. It will
>go higher, but not any lower. Channel A adjusts perfectly. All other
>adjustments on both channels work fine. Does anyone have any ideas as to
>how I can fix this?



 

Was the measurement of the cathodes of V3393 made with the plug-in set
to ADD mode?

Those voltages change depending on which channel of it both channels
are active.

I agree with what Don posted as well. Also check and compare the 500
ohm anode resistors of V3334, V3354 and V4334, V4354.

On Tue, 30 Apr 2013 09:36:58 -0500, Cliff White <w5cnw@arrl.net>
wrote:

All resistor values match between the two channels. R4337 and R4357 are
2.75K, instead of the 5.6K marked on the schematic, but the
corresponding resistors on channel A are also 2.75K. The voltage at the
cathode of V3393B is 39.8 volts, while the voltage on the cathode of
V3393A is 29.8 volts.

Respectfully,
Cliff White, W5CNW
w5cnw@arrl.net <mailto:w5cnw@arrl.net>
On 04/29/2013 09:43 PM, David wrote:

First I would check the values of the resistors and potentiometers in
the cathode network for V4334 and V4354 and the voltage at the cathode
of V3393B. Then I would check the values of the resistors in the
cathode network for V4364 and V4374.

If none of the above turned up anything, then I would swap the matched
pairs of tubes between channel A and channel B to see if the problem
moves to channel A.

On Mon, 29 Apr 2013 21:07:29 -0500, Cliff White <w5cnw@arrl.net
<mailto:w5cnw%40arrl.net>>
wrote:

I just finished repairing a Type CA plugin. Everything seems to have
calibrated just fine, with the exception of the channel B gain. It won't
go low enough. For example, if I apply a .1 volt P-P signal, at .05
volts/div, the lowest the gain will adjust to is about 2.3 divs. It will
go higher, but not any lower. Channel A adjusts perfectly. All other
adjustments on both channels work fine. Does anyone have any ideas as to
how I can fix this?


Cliff White <w5cnw@...>
 

Oops. You're right about V3393. I should have realized to check what mode it was in. Duh. Here are the voltages in each mode, all taken with a vom in DC mode:

Channel A only:
    A: 40.2
    B: 30.1

Channel B only:
    A: 30.1
    B: 40.0

Alternate:
    A: 40.2
    B: 40.0

Chopped:
    A: 35.2
    B: 35.2

Added:
    A: 39.9
    B: 39.8


That looks good to me. Agreed? I swapped the set of tubes between the channels, and now they both are a little bit high on gain. (?) For example, before the swap, the lowest channel B would go would be about 2.3 divs, and A would work fine. Now, both stop at about 2.1. (huh?). Random thought: Could the amp on my main unit have gone high? How can I check this without another mainframe or plugin? It's a 532.



On 04/30/2013 02:32 PM, David wrote:
 

Was the measurement of the cathodes of V3393 made with the plug-in set
to ADD mode?

Those voltages change depending on which channel of it both channels
are active.

I agree with what Don posted as well. Also check and compare the 500
ohm anode resistors of V3334, V3354 and V4334, V4354.

On Tue, 30 Apr 2013 09:36:58 -0500, Cliff White <w5cnw@...>
wrote:

>All resistor values match between the two channels. R4337 and R4357 are
>2.75K, instead of the 5.6K marked on the schematic, but the
>corresponding resistors on channel A are also 2.75K. The voltage at the
>cathode of V3393B is 39.8 volts, while the voltage on the cathode of
>V3393A is 29.8 volts.
>
>Respectfully,
>Cliff White, W5CNW
>w5cnw@... w5cnw@...>
>On 04/29/2013 09:43 PM, David wrote:
>>
>> First I would check the values of the resistors and potentiometers in
>> the cathode network for V4334 and V4354 and the voltage at the cathode
>> of V3393B. Then I would check the values of the resistors in the
>> cathode network for V4364 and V4374.
>>
>> If none of the above turned up anything, then I would swap the matched
>> pairs of tubes between channel A and channel B to see if the problem
>> moves to channel A.
>>
>> On Mon, 29 Apr 2013 21:07:29 -0500, Cliff White <w5cnw@...
>> >
>> wrote:
>>
>> >I just finished repairing a Type CA plugin. Everything seems to have
>> >calibrated just fine, with the exception of the channel B gain. It won't
>> >go low enough. For example, if I apply a .1 volt P-P signal, at .05
>> >volts/div, the lowest the gain will adjust to is about 2.3 divs. It will
>> >go higher, but not any lower. Channel A adjusts perfectly. All other
>> >adjustments on both channels work fine. Does anyone have any ideas as to
>> >how I can fix this?



Cliff White <w5cnw@...>
 

Oops. You're right about V3393. I should have realized to check what mode it was in. Duh. Here are the voltages in each mode, all taken with a vom in DC mode:

Channel A only:
    A: 40.2
    B: 30.1

Channel B only:
    A: 30.1
    B: 40.0

Alternate:
    A: 40.2
    B: 40.0

Chopped:
    A: 35.2
    B: 35.2

Added:
    A: 39.9
    B: 39.8


That looks good to me. Agreed? I swapped the set of tubes between the channels, and now they both are a little bit high on gain. (?) For example, before the swap, the lowest channel B would go would be about 2.3 divs, and A would work fine. Now, both stop at about 2.1. (huh?). Random thought: Could the amp on my main unit have gone high? How can I check this without another mainframe or plugin? It's a 532.



On 04/30/2013 02:32 PM, David wrote:
 

Was the measurement of the cathodes of V3393 made with the plug-in set
to ADD mode?

Those voltages change depending on which channel of it both channels
are active.

I agree with what Don posted as well. Also check and compare the 500
ohm anode resistors of V3334, V3354 and V4334, V4354.

On Tue, 30 Apr 2013 09:36:58 -0500, Cliff White <w5cnw@...>
wrote:

>All resistor values match between the two channels. R4337 and R4357 are
>2.75K, instead of the 5.6K marked on the schematic, but the
>corresponding resistors on channel A are also 2.75K. The voltage at the
>cathode of V3393B is 39.8 volts, while the voltage on the cathode of
>V3393A is 29.8 volts.
>
>Respectfully,
>Cliff White, W5CNW
>w5cnw@... w5cnw@...>
>On 04/29/2013 09:43 PM, David wrote:
>>
>> First I would check the values of the resistors and potentiometers in
>> the cathode network for V4334 and V4354 and the voltage at the cathode
>> of V3393B. Then I would check the values of the resistors in the
>> cathode network for V4364 and V4374.
>>
>> If none of the above turned up anything, then I would swap the matched
>> pairs of tubes between channel A and channel B to see if the problem
>> moves to channel A.
>>
>> On Mon, 29 Apr 2013 21:07:29 -0500, Cliff White <w5cnw@...
>> >
>> wrote:
>>
>> >I just finished repairing a Type CA plugin. Everything seems to have
>> >calibrated just fine, with the exception of the channel B gain. It won't
>> >go low enough. For example, if I apply a .1 volt P-P signal, at .05
>> >volts/div, the lowest the gain will adjust to is about 2.3 divs. It will
>> >go higher, but not any lower. Channel A adjusts perfectly. All other
>> >adjustments on both channels work fine. Does anyone have any ideas as to
>> >how I can fix this?



Cliff White <w5cnw@...>
 

I don't think this sent right the first time. Here it is again.

==============

Oops. You're right about V3393. I should have realized to check what mode it was in. Duh. Here are the voltages in each mode, all taken with a vom in DC mode:

Channel A only:
    A: 40.2
    B: 30.1

Channel B only:
    A: 30.1
    B: 40.0

Alternate:
    A: 40.2
    B: 40.0

Chopped:
    A: 35.2
    B: 35.2

Added:
    A: 39.9
    B: 39.8


That looks good to me. Agreed? I swapped the set of tubes between the channels, and now they both are a little bit high on gain. (?) For example, before the swap, the lowest channel B would go would be about 2.3 divs, and A would work fine. Now, both stop at about 2.1. (huh?). Random thought: Could the amp on my main unit have gone high? How can I check this without another mainframe or plugin? It's a 532.



On 04/30/2013 02:32 PM, David wrote:
 

Was the measurement of the cathodes of V3393 made with the plug-in set
to ADD mode?

Those voltages change depending on which channel of it both channels
are active.

I agree with what Don posted as well. Also check and compare the 500
ohm anode resistors of V3334, V3354 and V4334, V4354.

On Tue, 30 Apr 2013 09:36:58 -0500, Cliff White <w5cnw@...>
wrote:

>All resistor values match between the two channels. R4337 and R4357 are
>2.75K, instead of the 5.6K marked on the schematic, but the
>corresponding resistors on channel A are also 2.75K. The voltage at the
>cathode of V3393B is 39.8 volts, while the voltage on the cathode of
>V3393A is 29.8 volts.
>
>Respectfully,
>Cliff White, W5CNW
>w5cnw@... w5cnw@...>
>On 04/29/2013 09:43 PM, David wrote:
>>
>> First I would check the values of the resistors and potentiometers in
>> the cathode network for V4334 and V4354 and the voltage at the cathode
>> of V3393B. Then I would check the values of the resistors in the
>> cathode network for V4364 and V4374.
>>
>> If none of the above turned up anything, then I would swap the matched
>> pairs of tubes between channel A and channel B to see if the problem
>> moves to channel A.
>>
>> On Mon, 29 Apr 2013 21:07:29 -0500, Cliff White <w5cnw@...
>> >
>> wrote:
>>
>> >I just finished repairing a Type CA plugin. Everything seems to have
>> >calibrated just fine, with the exception of the channel B gain. It won't
>> >go low enough. For example, if I apply a .1 volt P-P signal, at .05
>> >volts/div, the lowest the gain will adjust to is about 2.3 divs. It will
>> >go higher, but not any lower. Channel A adjusts perfectly. All other
>> >adjustments on both channels work fine. Does anyone have any ideas as to
>> >how I can fix this?









kf5iyl <w5cnw@...>
 

Oops. You're right about V3393. I should have realized to check what mode it was in. Duh. Here are the voltages in each mode, all taken with a vom in DC mode:

Channel A only:
A: 40.2
B: 30.1

Channel B only:
A: 30.1
B: 40.0

Alternate:
A: 40.2
B: 40.0

Chopped:
A: 35.2
B: 35.2

Added:
A: 39.9
B: 39.8

That looks good to me. Agreed? I swapped the set of tubes between the channels, and now they both are a little bit high on gain. (?) For example, before the swap, the lowest channel B would go would be about 2.3 divs, and A would work fine. Now, both stop at about 2.1. (huh?). Random thought: Could the amp on my main unit have gone high? How can I check this without another mainframe or plugin? It's a 532.

--- In TekScopes@yahoogroups.com, David <davidwhess@...> wrote:

Was the measurement of the cathodes of V3393 made with the plug-in set
to ADD mode?

Those voltages change depending on which channel of it both channels
are active.

I agree with what Don posted as well. Also check and compare the 500
ohm anode resistors of V3334, V3354 and V4334, V4354.

On Tue, 30 Apr 2013 09:36:58 -0500, Cliff White <w5cnw@...>
wrote:

All resistor values match between the two channels. R4337 and R4357 are
2.75K, instead of the 5.6K marked on the schematic, but the
corresponding resistors on channel A are also 2.75K. The voltage at the
cathode of V3393B is 39.8 volts, while the voltage on the cathode of
V3393A is 29.8 volts.

Respectfully,
Cliff White, W5CNW
w5cnw@... <mailto:w5cnw@...>
On 04/29/2013 09:43 PM, David wrote:

First I would check the values of the resistors and potentiometers in
the cathode network for V4334 and V4354 and the voltage at the cathode
of V3393B. Then I would check the values of the resistors in the
cathode network for V4364 and V4374.

If none of the above turned up anything, then I would swap the matched
pairs of tubes between channel A and channel B to see if the problem
moves to channel A.

On Mon, 29 Apr 2013 21:07:29 -0500, Cliff White <w5cnw@...
<mailto:w5cnw%40arrl.net>>
wrote:

I just finished repairing a Type CA plugin. Everything seems to have
calibrated just fine, with the exception of the channel B gain. It won't
go low enough. For example, if I apply a .1 volt P-P signal, at .05
volts/div, the lowest the gain will adjust to is about 2.3 divs. It will
go higher, but not any lower. Channel A adjusts perfectly. All other
adjustments on both channels work fine. Does anyone have any ideas as to
how I can fix this?


 

Cliff,

Are you sure the "low" channel is really "low"?
Could it be that the higher gain channel is actually too high ?
If the mainframe vertical gain is too far off, you may get one channel which will adjust to it while the other ch cannot.
If you have the extender with the banana jack on one side, you can adjust the "mainframe" gain.
Also, the trace should be reasonably well-centered with no plug-in installed.
A TU-7 plugin would be ideal for setting the mainframe gain but I suspect those are pretty rare.
Also, make sure both the Var V/div knobs are in their detent position.
 
HankC, Boston
WA1HOS


 

I could not find any specifications for the 500 series vertical
plug-in interface voltage levels. If you know those, then you can
certainly standardize the mainframe with just an AC voltmeter and low
frequency signal generator or even the calibrator output. Just
measure the AC voltage at the vertical plug-in interface.

On Tue, 30 Apr 2013 15:32:09 -0700 (PDT), HankC <hankc918@yahoo.com>
wrote:

Cliff,

Are you sure the "low" channel is really "low"?
Could it be that the higher gain channel is actually too high ?
If the mainframe vertical gain is too far off, you may get one channel which will adjust to it while the other ch cannot.
If you have the extender with the banana jack on one side, you can adjust the "mainframe" gain.
Also, the trace should be reasonably well-centered with no plug-in installed.
A TU-7 plugin would be ideal for setting the mainframe gain but I suspect those are pretty rare.
Also, make sure both the Var V/div knobs are in their detent position.

 
HankC, Boston
WA1HOS


Dave Wise
 

67.5VDC common-mode, 0.1V/div differential.

Dave Wise

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf Of David
Sent: Tuesday, April 30, 2013 3:47 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: Type CA Channel B Gain Adj Problem

I could not find any specifications for the 500 series vertical
plug-in interface voltage levels. If you know those, then you can
certainly standardize the mainframe with just an AC voltmeter and low
frequency signal generator or even the calibrator output. Just
measure the AC voltage at the vertical plug-in interface.

On Tue, 30 Apr 2013 15:32:09 -0700 (PDT), HankC <hankc918@yahoo.com>
wrote:

Cliff,

Are you sure the "low" channel is really "low"?
Could it be that the higher gain channel is actually too high ?
If the mainframe vertical gain is too far off, you may get one channel which will adjust to it while the other ch cannot.
If you have the extender with the banana jack on one side, you can adjust the "mainframe" gain.
Also, the trace should be reasonably well-centered with no plug-in installed.
A TU-7 plugin would be ideal for setting the mainframe gain but I suspect those are pretty rare.
Also, make sure both the Var V/div knobs are in their detent position.

 
HankC, Boston
WA1HOS

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

Yahoo! Groups Links


 

Did Tektronix write that down somewhere? That sounds like it comes
from a service manual I should print up.

On Tue, 30 Apr 2013 15:49:58 -0700, David Wise
<david_wise@phoenix.com> wrote:

67.5VDC common-mode, 0.1V/div differential.

Dave Wise

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf Of David
Sent: Tuesday, April 30, 2013 3:47 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: Type CA Channel B Gain Adj Problem

I could not find any specifications for the 500 series vertical
plug-in interface voltage levels. If you know those, then you can
certainly standardize the mainframe with just an AC voltmeter and low
frequency signal generator or even the calibrator output. Just
measure the AC voltage at the vertical plug-in interface.


Dave Wise
 

Sorry, can't remember.

Dave Wise

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf Of David
Sent: Tuesday, April 30, 2013 4:00 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: Type CA Channel B Gain Adj Problem

Did Tektronix write that down somewhere? That sounds like it comes
from a service manual I should print up.

On Tue, 30 Apr 2013 15:49:58 -0700, David Wise
<david_wise@phoenix.com> wrote:

67.5VDC common-mode, 0.1V/div differential.

Dave Wise

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf Of David
Sent: Tuesday, April 30, 2013 3:47 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: Type CA Channel B Gain Adj Problem

I could not find any specifications for the 500 series vertical
plug-in interface voltage levels. If you know those, then you can


teamlarryohio
 

The TU-7 manual (on bama) mentions it as .4V P-P is 4 div.
-ls-


David Wise <david_wise@phoenix.com> wrote:

Sorry, can't remember.

Dave Wise

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf Of David
Sent: Tuesday, April 30, 2013 4:00 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: Type CA Channel B Gain Adj Problem

Did Tektronix write that down somewhere? That sounds like it comes
from a service manual I should print up.

On Tue, 30 Apr 2013 15:49:58 -0700, David Wise
<david_wise@phoenix.com> wrote:

67.5VDC common-mode, 0.1V/div differential.

Dave Wise

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf Of David
Sent: Tuesday, April 30, 2013 3:47 PM
To: TekScopes@yahoogroups.com
Subject: Re: [TekScopes] Re: Type CA Channel B Gain Adj Problem

I could not find any specifications for the 500 series vertical
plug-in interface voltage levels. If you know those, then you can

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

Yahoo! Groups Links



Don Black <donald_black@...>
 

I've checked bot the CA and 536 manuals and neither seem to have the usual waveforms that would indicate the signal level from the plugin to the mainframe. However in the TU2 test plugin (attached) it indicates 0.1 volt per division. You should be able to measure this at the mainframe and see if it gives the correct sensitivity. I suggest looking for more than one divisions at 0.1 volts per division. You'll need another scope for this, however any scope will do, you can check it against the calibrator if necessary.
Incidentally, are you relying on the calibrator signal for your measurements? It's always possible that's drifted and may be fooling you. You could measure an AC signal with a meter, calculate its peak to peak voltage (V RMS X 2√2) and see how that agrees with your cal signal.
Don Black.

On 30-Apr-13 12:07 PM, Cliff White wrote:
 

I just finished repairing a Type CA plugin. Everything seems to have calibrated just fine, with the exception of the channel B gain. It won't go low enough. For example, if I apply a .1 volt P-P signal, at .05 volts/div, the lowest the gain will adjust to is about 2.3 divs. It will go higher, but not any lower. Channel A adjusts perfectly. All other adjustments on both channels work fine. Does anyone have any ideas as to how I can fix this?


--
Respectfully,
Cliff White, W5CNW
w5cnw@...


Cliff White <w5cnw@...>
 

I've been using the calibrator from a different scope, which was calibrated a few weeks ago, so I'm pretty sure it's right. I do have two other working scopes right now, just none of the same series. I'll set the interface to the .1 volt/div and see if that fixes anything. Is the DC voltage it's floating on supposed to be calibrated as well?


Respectfully,
Cliff White, W5CNW
w5cnw@...

On 05/01/2013 01:43 AM, Don Black wrote:
 

I've checked bot the CA and 536 manuals and neither seem to have the usual waveforms that would indicate the signal level from the plugin to the mainframe. However in the TU2 test plugin (attached) it indicates 0.1 volt per division. You should be able to measure this at the mainframe and see if it gives the correct sensitivity. I suggest looking for more than one divisions at 0.1 volts per division. You'll need another scope for this, however any scope will do, you can check it against the calibrator if necessary.
Incidentally, are you relying on the calibrator signal for your measurements? It's always possible that's drifted and may be fooling you. You could measure an AC signal with a meter, calculate its peak to peak voltage (V RMS X 2√2) and see how that agrees with your cal signal.
Don Black.

On 30-Apr-13 12:07 PM, Cliff White wrote:

 

I just finished repairing a Type CA plugin. Everything seems to have calibrated just fine, with the exception of the channel B gain. It won't go low enough. For example, if I apply a .1 volt P-P signal, at .05 volts/div, the lowest the gain will adjust to is about 2.3 divs. It will go higher, but not any lower. Channel A adjusts perfectly. All other adjustments on both channels work fine. Does anyone have any ideas as to how I can fix this?


--
Respectfully,
Cliff White, W5CNW
w5cnw@...



Cliff White <w5cnw@...>
 

Something doesn't quite smell right about the .1v/div thing. I just tried to adjust it, and here's what I got: I have a 0.2v signal, with the plugin set to .05 volts/div, which should be 4 divs, right? With the CA gain turned all the way down (just channel A, B isn't too much different), I'm seeing 4.2 divs on the mainframe, 0.18 volts on the interface. With the CA gain all the way up, I'm seeing 6.7 divs on mainframe, 0.29 volts on the interface. This almost looks to me like it really should be .05 volts/div at the interface? Thoughts?


Respectfully,
Cliff White, W5CNW
w5cnw@...

On 05/01/2013 01:43 AM, Don Black wrote:
 

I've checked bot the CA and 536 manuals and neither seem to have the usual waveforms that would indicate the signal level from the plugin to the mainframe. However in the TU2 test plugin (attached) it indicates 0.1 volt per division. You should be able to measure this at the mainframe and see if it gives the correct sensitivity. I suggest looking for more than one divisions at 0.1 volts per division. You'll need another scope for this, however any scope will do, you can check it against the calibrator if necessary.
Incidentally, are you relying on the calibrator signal for your measurements? It's always possible that's drifted and may be fooling you. You could measure an AC signal with a meter, calculate its peak to peak voltage (V RMS X 2√2) and see how that agrees with your cal signal.
Don Black.

On 30-Apr-13 12:07 PM, Cliff White wrote:

 

I just finished repairing a Type CA plugin. Everything seems to have calibrated just fine, with the exception of the channel B gain. It won't go low enough. For example, if I apply a .1 volt P-P signal, at .05 volts/div, the lowest the gain will adjust to is about 2.3 divs. It will go higher, but not any lower. Channel A adjusts perfectly. All other adjustments on both channels work fine. Does anyone have any ideas as to how I can fix this?


--
Respectfully,
Cliff White, W5CNW
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Don Black <donald_black@...>
 

The DC is the operating bias voltage for the 536 input stage and should be ignored, it's the peak to peak signal voltage you need to measure.
However I think there's a trap. The TU-2 calibrator only applies the signal to one of the differential inputs to the 536, the other input is AC grounded. That should be 0.1 volt per division according to the TU-2 manual. However if you use the signal through the CA preamplifier. it should enter the 536 as a differential signal, half at each input point but out of phase so they add. It's the total signal between the two inputs that's important so I'd expect to see 50 mV per division on each of the inputs, the grids of V304 and V324 (pins 1 and 3 of the interconnecting socket). They should be identical but of opposite phase, however I'd measure both and add them together in case the CA isn't exactly balanced. If your test scope has differential input you could directly measure the input between the two grids.
Since the error isn't too great if the signals aren't close to what they should be then let me know and I'll double check but I think I'm right. It's a pity they don't have waveforms in the manuals.
Anyone familiar with these models with anything to add or thinks I've made an error, please jump in.

Don Black.

On 01-May-13 11:33 PM, Cliff White wrote:
 

I've been using the calibrator from a different scope, which was calibrated a few weeks ago, so I'm pretty sure it's right. I do have two other working scopes right now, just none of the same series. I'll set the interface to the .1 volt/div and see if that fixes anything. Is the DC voltage it's floating on supposed to be calibrated as well?


Respectfully,
Cliff White, W5CNW
w5cnw@...
On 05/01/2013 01:43 AM, Don Black wrote:
 

I've checked bot the CA and 536 manuals and neither seem to have the usual waveforms that would indicate the signal level from the plugin to the mainframe. However in the TU2 test plugin (attached) it indicates 0.1 volt per division. You should be able to measure this at the mainframe and see if it gives the correct sensitivity. I suggest looking for more than one divisions at 0.1 volts per division. You'll need another scope for this, however any scope will do, you can check it against the calibrator if necessary.
Incidentally, are you relying on the calibrator signal for your measurements? It's always possible that's drifted and may be fooling you. You could measure an AC signal with a meter, calculate its peak to peak voltage (V RMS X 2√2) and see how that agrees with your cal signal.
Don Black.

On 30-Apr-13 12:07 PM, Cliff White wrote:

 

I just finished repairing a Type CA plugin. Everything seems to have calibrated just fine, with the exception of the channel B gain. It won't go low enough. For example, if I apply a .1 volt P-P signal, at .05 volts/div, the lowest the gain will adjust to is about 2.3 divs. It will go higher, but not any lower. Channel A adjusts perfectly. All other adjustments on both channels work fine. Does anyone have any ideas as to how I can fix this?


--
Respectfully,
Cliff White, W5CNW
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