Topics

2467B focus/astigmatism anomaly...

Chuck Harris
 

Hi Gang,

I get about one 2467B to work on for every 30, 2465B's, so I haven't
got tons of experience with them. I don't have one on my bench, so
ditto the problem. They calibrate just like the 2465B, but I don't
know much about living with one.

So, I got a customer's 2467B that had focus issues where the focus was
changing at will. The previous owner really worked over the HV board
looking for the problem... my customer inherited those issues...

I traced down about a half dozen problems, ranging from bad transistors,
lead dress of the focus resistors, wires on the HV module that were
down to 1 strand... maybe less?, cut up teflon insulation back to the
CRT socket... lots of flux, and other dirt on the board...the usual
stupid stuff.

But after fixing all of that, there is still an anomaly.

If I let the scope warm up, put a cross hair in the center of the screen,
do a fine focus/astigmatism adjustment, turn the display, and intensity
off, to protect the CRT, and walk away for a couple of hours. When I turn
the intensities back up, the screen will be fuzzy at normal viewing
intensity levels..

The fuzziness can't be cleared by using the focus knob, only the little
screwdriver slotted astigmatism control.

I put a DVM on the astigmatism grid, and the value is rock solid. The
changes in focus are not the result of changes in astigmatism voltage, but
a change in astigmatism voltage is necessary to bring back focus.

Sharpen things up, turn off the intensities, walk away, and in another
couple of hours, it will be blurry again. Only correctable by adjusting
the astigmatism.

As an interesting side note, just before the internal timer turns off the
CRT beam, the beam and readout will get blurry, but when I move any control
to restore the display, it will return to sharpness once again.


OK...

So, I have a 2465B on my shelves that has a bad CRT, so I thought I would
see what it does under similar conditions:

It does the same thing! A little bit less so than my customer's scope, but
I definitely have to chase the astigmatism around if I leave it for a couple
of hours with the beam turned off.

Anybody notice any astigmatism weirdness with their 2467B's???

Thanks!

-Chuck Harris

OBTW, I read in the operator's guide that the 2467B will first turn the
display down, after extended inactivity, before it actually goes into shutdown...
maybe turning the display down involves blurring the focus???

satbeginner
 

Hi Chuck,

As test, I fired up my 2467B, showing an Analog Clock display in X-Y mode.

Will let it warm up,
find the sharpest display and readout using both front focus and astig,
then turn down display intensity and readout and check in two hours.

TBC

Leo

satbeginner
 

Follow up:

After about 2h45min and turning up both the intensity and readout, the display and readout were still in the sharpest setting.

Adjusting focus and/or astig would make the screen less focussed.....

I would suggest to (before and after) check all relevant voltages on the CRT.

Geometry, edge focus, y-axis alignment, and the components around Q4422, Q4402 and Q4403.

Maybe a cold solder joint in that area?

Un saludo,

Leo

Chuck Harris
 

Hi Leo,

Thanks for doing the test. The problem with making
measurements in the focus area of the 2467B is the
extreme high impedance of the circuitry. Even my
100M HV probe loads the circuits down visibly.

However, the low impedance CRT voltages:

edge focus, geometry, astigmatism, PDD lens and wall band,
anode 1, are all rock solid. As is the cathode of the
CRT.

So, that points to the actual anode voltage and the
focus voltage... neither of which will behave well when
measured with any probes I have.

It would seem to me that the only way for the astigmatism
voltage required for good focus to shift would be if the
anode voltage changed.

The change in the anode voltage wouldn't necessarily cause
a corresponding shift in the focus pot's position for best
focus, because the focus electrode's voltage is derived from
the cathode supply...

Q4402 was found earlier to be shorted. It was replaced with
new. I suppose it might be a good idea to figure out how it
got to be bad. Perhaps a problem with C4403 did the deed?

Puzzling.

-Chuck Harris


satbeginner wrote:

Follow up:

After about 2h45min and turning up both the intensity and readout, the display and readout were still in the sharpest setting.

Adjusting focus and/or astig would make the screen less focussed.....

I would suggest to (before and after) check all relevant voltages on the CRT.

Geometry, edge focus, y-axis alignment, and the components around Q4422, Q4402 and Q4403.

Maybe a cold solder joint in that area?

Un saludo,

Leo



Jim Ford
 

Hmmm... maybe use an HPAK 34401A DMM in high resistance mode?  Don't know what your anode voltage is - it could exceed the 34401A's range.  Just a thought.Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Chuck Harris <cfharris@...> Date: 8/16/19 11:54 AM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 2467B focus/astigmatism anomaly... Hi Leo,Thanks for doing the test.  The problem with makingmeasurements in the focus area of the 2467B is theextreme high impedance of the circuitry.  Even my100M HV probe loads the circuits down visibly.However, the low impedance CRT voltages:edge focus, geometry, astigmatism, PDD lens and wall band,anode 1, are all rock solid.  As is the cathode of theCRT.So, that points to the actual anode voltage and thefocus voltage... neither of which will behave well whenmeasured with any probes I have.It would seem to me that the only way for the astigmatismvoltage required for good focus to shift would be if theanode voltage changed.The change in the anode voltage wouldn't necessarily causea corresponding shift in the focus pot's position for bestfocus, because the focus electrode's voltage is derived fromthe cathode supply...Q4402 was found earlier to be shorted.  It was replaced withnew.  I suppose it might be a good idea to figure out how itgot to be bad.  Perhaps a problem with C4403 did the deed?Puzzling.-Chuck Harrissatbeginner wrote:> Follow up:> > After about 2h45min and turning up both the intensity and readout,  the display and readout were still in the sharpest setting.> > Adjusting focus and/or astig would make the screen less focussed.....> > I would suggest to (before and after) check all relevant voltages on the CRT.> > Geometry, edge focus, y-axis alignment, and the components around Q4422, Q4402 and Q4403.> > Maybe a cold solder joint in that area?> > Un saludo,> > Leo> > > >

Chuck Harris
 

The anode voltage is 15KV... I the 34401 tops out at 1KV with 10M input
resistance. Not even close.

-Chuck Harris

Jim Ford wrote:

Hmmm... maybe use an HPAK 34401A DMM in high resistance mode? Don't know what your anode voltage is - it could exceed the 34401A's range. Just a thought.Jim Ford Sent

Lawrance A. Schneider
 

On Aug 16, 2019, at 10:08 AM, Chuck Harris <cfharris@...> wrote:

Hi Gang,

I get about one 2467B to work on for every 30, 2465B's, so I haven't
got tons of experience with them. I don't have one on my bench, so
ditto the problem. They calibrate just like the 2465B, but I don't
know much about living with one.

So, I got a customer's 2467B that had focus issues where the focus was
changing at will. The previous owner really worked over the HV board
looking for the problem... my customer inherited those issues...

I traced down about a half dozen problems, ranging from bad transistors,
lead dress of the focus resistors, wires on the HV module that were
down to 1 strand... maybe less?, cut up teflon insulation back to the
CRT socket... lots of flux, and other dirt on the board...the usual
stupid stuff.

But after fixing all of that, there is still an anomaly.

If I let the scope warm up, put a cross hair in the center of the screen,
do a fine focus/astigmatism adjustment, turn the display, and intensity
off, to protect the CRT, and walk away for a couple of hours. When I turn
the intensities back up, the screen will be fuzzy at normal viewing
intensity levels..

The fuzziness can't be cleared by using the focus knob, only the little
screwdriver slotted astigmatism control.

I put a DVM on the astigmatism grid, and the value is rock solid. The
changes in focus are not the result of changes in astigmatism voltage, but
a change in astigmatism voltage is necessary to bring back focus.

Sharpen things up, turn off the intensities, walk away, and in another
couple of hours, it will be blurry again. Only correctable by adjusting
the astigmatism.

As an interesting side note, just before the internal timer turns off the
CRT beam, the beam and readout will get blurry, but when I move any control
to restore the display, it will return to sharpness once again.


OK...

So, I have a 2465B on my shelves that has a bad CRT, so I thought I would
see what it does under similar conditions:

It does the same thing! A little bit less so than my customer's scope, but
I definitely have to chase the astigmatism around if I leave it for a couple
of hours with the beam turned off.

Anybody notice any astigmatism weirdness with their 2467B's???

Thanks!

-Chuck Harris

OBTW, I read in the operator's guide that the 2467B will first turn the
display down, after extended inactivity, before it actually goes into shutdown...
maybe turning the display down involves blurring the focus???


Yes, I’m have a focus problem. I’ve not tackled it yet. I have a thousand other things to do first. Besides, when I do tackle it, I most likely be hoping you have advise for me.

larry

Jim Ford
 

Yep, I figured it was a long shot.Thanks, Chuck. JimSent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Chuck Harris <cfharris@...> Date: 8/16/19 12:48 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 2467B focus/astigmatism anomaly... The anode voltage is 15KV... I the 34401 tops out at 1KV with 10M inputresistance.  Not even close.-Chuck HarrisJim Ford wrote:> Hmmm... maybe use an HPAK 34401A DMM in high resistance mode?  Don't know what your anode voltage is - it could exceed the 34401A's range.  Just a thought.Jim Ford Sent

Chuck Harris
 

I thought of using a Fluke differential voltmeter that does have virtually
infinite input impedance when it is in balance, but it too is only 1KV.

I am going to have to figure out a way to sneak sideways into this problem.

-Chuck Harris

Jim Ford wrote:

Yep, I figured it was a long shot.Thanks, Chuck. JimSent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Chuck Harris <cfharris@...> Date: 8/16/19 12:48 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 2467B focus/astigmatism anomaly... The anode voltage is 15KV... I the 34401 tops out at 1KV with 10M inputresistance. Not even close.-Chuck HarrisJim Ford wrote:> Hmmm... maybe use an HPAK 34401A DMM in high resistance mode? Don't know what your anode voltage is - it could exceed the 34401A's range. Just a thought.Jim Ford Sent

george edmonds
 

Why don't you use a Fluke 40KV probe these are designed to work with a 10M Ohm input DVM

George

On Friday, August 16, 2019, 9:10:30 PM GMT+1, Chuck Harris <cfharris@...> wrote:

I thought of using a Fluke differential voltmeter that does have virtually
infinite input impedance when it is in balance, but it too is only 1KV.

I am going to have to figure out a way to sneak sideways into this problem.

-Chuck Harris

Jim Ford wrote:
Yep, I figured it was a long shot.Thanks, Chuck. JimSent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Chuck Harris <cfharris@...> Date: 8/16/19  12:48 PM  (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 2467B focus/astigmatism anomaly... The anode voltage is 15KV... I the 34401 tops out at 1KV with 10M inputresistance.  Not even close.-Chuck HarrisJim Ford wrote:> Hmmm... maybe use an HPAK 34401A DMM in high resistance mode?  Don't know what your anode voltage is - it could exceed the 34401A's range.  Just a thought.Jim Ford Sent

Dave Wise
 

If you have another power supply that can make 15KV, you could assemble a differential voltmeter using the supply, a battery-powered voltmeter as null detector, and another voltmeter to measure the supply output once you have it nulled. The detector should have autoranging turned off, and have protection diodes across its input.

I'm feeling a mad-scientist vibe, makes me wish I had a 15KV supply :)

Dave Wise

Let my creation LIIIIIVE!!!!!

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: Friday, August 16, 2019 1:10 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 2467B focus/astigmatism anomaly...

I thought of using a Fluke differential voltmeter that does have virtually
infinite input impedance when it is in balance, but it too is only 1KV.

I am going to have to figure out a way to sneak sideways into this problem.

-Chuck Harris

Jim Ford wrote:
Yep, I figured it was a long shot.Thanks, Chuck. JimSent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Chuck Harris <cfharris@...> Date: 8/16/19 12:48 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 2467B focus/astigmatism anomaly... The anode voltage is 15KV... I the 34401 tops out at 1KV with 10M inputresistance. Not even close.-Chuck HarrisJim Ford wrote:> Hmmm... maybe use an HPAK 34401A DMM in high resistance mode? Don't know what your anode voltage is - it could exceed the 34401A's range. Just a thought.Jim Ford Sent

Chuck Harris
 

That is where I went first, but when my 100M Keithley probe
is applied to the focus grid, it pulls the scope out of focus.
It is a problem when the measurement equipment adversely
affects the measured circuit.

-Chuck Harris


george edmonds via Groups.Io wrote:

Why don't you use a Fluke 40KV probe these are designed to work with a 10M Ohm input DVM

George
On Friday, August 16, 2019, 9:10:30 PM GMT+1, Chuck Harris <cfharris@...> wrote:

I thought of using a Fluke differential voltmeter that does have virtually
infinite input impedance when it is in balance, but it too is only 1KV.

I am going to have to figure out a way to sneak sideways into this problem.

-Chuck Harris

Chuck Harris
 

You're scaring me Dave....

-Chuck Harris

Dave Wise wrote:

If you have another power supply that can make 15KV, you could assemble a differential voltmeter using the supply, a battery-powered voltmeter as null detector, and another voltmeter to measure the supply output once you have it nulled. The detector should have autoranging turned off, and have protection diodes across its input.

I'm feeling a mad-scientist vibe, makes me wish I had a 15KV supply :)

Dave Wise

Let my creation LIIIIIVE!!!!!

george edmonds
 

Hi Chuck

The Fluke 40KV probe is 1,000M input, The only other quick solution is an electrostatic meter, but I doubt it would have the resolution that you require.

George.

On Friday, August 16, 2019, 10:30:26 PM GMT+1, Chuck Harris <cfharris@...> wrote:

That is where I went first, but when my 100M Keithley probe
is applied to the focus grid, it pulls the scope out of focus.
It is a problem when the measurement equipment adversely
affects the measured circuit.

-Chuck Harris


george edmonds via Groups.Io wrote:
  Why don't you use a Fluke 40KV probe these are designed to work with a 10M Ohm input DVM

George
      On Friday, August 16, 2019, 9:10:30 PM GMT+1, Chuck Harris <cfharris@...> wrote:
 
  I thought of using a Fluke differential voltmeter that does have virtually
infinite input impedance when it is in balance, but it too is only 1KV.

I am going to have to figure out a way to sneak sideways into this problem.

-Chuck Harris

Dave Seiter
 

Who was it that was building the "frankenscope" about 13 years ago?
-Dave (another one)

On Friday, August 16, 2019, 02:36:18 PM PDT, Chuck Harris <cfharris@...> wrote:

You're scaring me Dave....

-Chuck Harris

Dave Wise wrote:
If you have another power supply that can make 15KV, you could assemble a differential voltmeter using the supply, a battery-powered voltmeter as null detector, and another voltmeter to measure the supply output once you have it nulled.  The detector should have autoranging turned off, and have protection diodes across its input.

I'm feeling a mad-scientist vibe, makes me wish I had a 15KV supply :)

Dave Wise

Let my creation LIIIIIVE!!!!!

John Griessen
 

On 8/16/19 3:49 PM, Dave Wise wrote:
I'm feeling a mad-scientist vibe, makes me wish I had a 15KV supply
I've got a 40kV Glassman 2kW I'm in the middle of converting from positive to negative.

Chuck Harris
 

Hi George,

Yes, you are right... but then, my keithley 1600A is also
1000M input impedance...

I just tried the keithley on the focus grid, and it did
*not* load it down noticeably. Clearly, I must have tried
some other scheme the last time I measured it.

I am not sure how I can leave this huge probe connected
given that it isn't amenable to a gripper clip. A skyhook,
I guess...

-Chuck Harris

george edmonds via Groups.Io wrote:

Hi Chuck

The Fluke 40KV probe is 1,000M input, The only other quick solution is an electrostatic meter, but I doubt it would have the resolution that you require.

George.
On Friday, August 16, 2019, 10:30:26 PM GMT+1, Chuck Harris <cfharris@...> wrote:

That is where I went first, but when my 100M Keithley probe
is applied to the focus grid, it pulls the scope out of focus.
It is a problem when the measurement equipment adversely
affects the measured circuit.

-Chuck Harris

Chuck Harris
 

Sounds like someone is making him a Farnsworth Fusor.

-Chuck Harris

John Griessen wrote:

On 8/16/19 3:49 PM, Dave Wise wrote:
I'm feeling a mad-scientist vibe, makes me wish I had a 15KV supply
I've got a 40kV Glassman 2kW I'm in the middle of converting from positive to negative.



george edmonds
 

Hi Chuck

I am quite amused by the 40KV probe as rule one is that you do not hand hold such an item when applied to power.

Best of luck

George

On Friday, August 16, 2019, 11:02:22 PM GMT+1, Chuck Harris <cfharris@...> wrote:

Hi George,

Yes, you are right... but then, my keithley 1600A is also
1000M input impedance...

I just tried the keithley on the focus grid, and it did
*not* load it down noticeably.  Clearly, I must have tried
some other scheme the last time I measured it.

I am not sure how I can leave this huge probe connected
given that it isn't amenable to a gripper clip.  A skyhook,
I guess...

-Chuck Harris

george edmonds via Groups.Io wrote:
  Hi Chuck

The Fluke 40KV probe is 1,000M input, The only other quick solution is an electrostatic meter, but I doubt it would have the resolution that you require.

George.
      On Friday, August 16, 2019, 10:30:26 PM GMT+1, Chuck Harris <cfharris@...> wrote:
 
  That is where I went first, but when my 100M Keithley probe
is applied to the focus grid, it pulls the scope out of focus.
It is a problem when the measurement equipment adversely
affects the measured circuit.

-Chuck Harris

 

Chuck,
I assume that after fiddling with the astig setting, you always end up at the setting before turning down intensity?
Did you try not touching the astig setting after turning intensity back up? Will focus eventually return even when not touching astig?
I'm thinking about leakage somewhere or lack of DC coupling (almost the same here).

With intensity off, beam current goes to almost zero.

I have seen setups where the astig electrode is closer to the cathode than the focus electrode. That does not seem to be so in this CRT but could it be that the dot distortion caused by disturbing the round shape of the beam (by operating the astig control) after upping the intensity causes a slight charge leak to/from the focus hole in the focus electrode, slightly adjusting the potential on the focus electrode?
This raises the question of whether the "dark" situation might actually be the correct situation, which is then *disturbed* after upping intensity or the other way around?
I would expect the currents on the focus and astig electrodes to be virtually zero during normal operation but the beam could approach the edge of the focus hole when it's not round, causing some leakage.
Perhaps replacing C4403 (since it carries a substantial DC voltage during operation, a slight leakage may disturb things) would be a good idea without having to resort to more extreme measures to see the high impedance HV's. As you say, regular HV probes (like a Fluke 40K8, for DC) or a Tek P6015A or the like won't be of much help in many places here.

Raymond