2445B focus problem

[Grant Erwin]

I have a 2445B scope on which I can not adjust focus to obtain a clear
sharp trace. The best focus is achieved somewhere in the middle of the
range of the focus pot which leads me to believe that this isn't just
a pot which has drifted.

This is a scope purchased under warranty. Should I return it or try to
repair it? Any ideas what may be wrong?

To email me see http://www.tinyisland.com/email.html

Thanks!

Grant Erwin
Kirkland, Washington

 

[Bob M.]

How about the astigmatism control, usually a screwdriver adjustment on the
front panel? Between that and the focus pot it should be possible to get a
clear trace everywhere.

Does it do this with no input signal, or only when you have it connected to
something? The 20 MHz bandwidth switch cleans the trace up nicely on my
2445, otherwise it is fairly broad.

If that doesn't do it, I'd go for the warranty first.

Bob M.
======
"Grant Erwin" <grantNOSPAM@kirkland.net> wrote in message
news:vgr6vmp0r5dn7d@corp.supernews.com...

I have a 2445B scope on which I can not adjust focus to obtain a clear
sharp trace. The best focus is achieved somewhere in the middle of the
range of the focus pot which leads me to believe that this isn't just
a pot which has drifted.

This is a scope purchased under warranty. Should I return it or try to
repair it? Any ideas what may be wrong?

To email me see http://www.tinyisland.com/email.html

Thanks!

Grant Erwin
Kirkland, Washington

 

[Grant Erwin]

Tweezing the astigmatism pot did actually help quite a bit. It's now
probably usable. I was just looking at the DC traces and the lettering.
This scope was shipped without proper (original) packing material and
it may have just bonked the front panel pots a little.

My big concern is if the CRT is gassy - that is a killer when buying
old Tek scopes. Even when you could get replacements they would cost
as much as adding a room on your house!

I've heard that on 2215 scopes there is a resistor string focus
setting network which drifts. I've looked at the schematic for
the focus control electronics on the 24XX scopes and it is an
actual DC amplifier. I don't think this is a resistor drift issue.

As I do have a parts scope available, I do also have the option to
swap the high voltage boards. I don't know if that would cause the
scope to go out of calibration, however.

Grant Erwin
Kirkland, Washington

Bob M. wrote:

How about the astigmatism control, usually a screwdriver adjustment on the
front panel? Between that and the focus pot it should be possible to get a
clear trace everywhere.

Does it do this with no input signal, or only when you have it connected to
something? The 20 MHz bandwidth switch cleans the trace up nicely on my
2445, otherwise it is fairly broad.

If that doesn't do it, I'd go for the warranty first.

Bob M.
======
"Grant Erwin" <grantNOSPAM@kirkland.net> wrote in message
news:vgr6vmp0r5dn7d@corp.supernews.com...

I have a 2445B scope on which I can not adjust focus to obtain a clear
sharp trace. The best focus is achieved somewhere in the middle of the
range of the focus pot which leads me to believe that this isn't just
a pot which has drifted.

This is a scope purchased under warranty. Should I return it or try to
repair it? Any ideas what may be wrong?

To email me see http://www.tinyisland.com/email.html

Thanks!

Grant Erwin
Kirkland, Washington

 

[Jim Yanik]

"Bob M." <xxxxx@yyyy.zzz> wrote in
newsHadnfSoRPo-apCiXTWJgA@comcast.com:

How about the astigmatism control, usually a screwdriver adjustment on
the front panel? Between that and the focus pot it should be possible
to get a clear trace everywhere.

Does it do this with no input signal, or only when you have it
connected to something? The 20 MHz bandwidth switch cleans the trace
up nicely on my 2445, otherwise it is fairly broad.

If that doesn't do it, I'd go for the warranty first.

Bob M.
======
"Grant Erwin" <grantNOSPAM@kirkland.net> wrote in message
news:vgr6vmp0r5dn7d@corp.supernews.com...
I have a 2445B scope on which I can not adjust focus to obtain a
clear sharp trace. The best focus is achieved somewhere in the middle
of the range of the focus pot which leads me to believe that this
isn't just a pot which has drifted.

This is a scope purchased under warranty. Should I return it or try
to repair it? Any ideas what may be wrong?

To email me see http://www.tinyisland.com/email.html

Thanks!

Grant Erwin
Kirkland, Washington

This is good advice.IF all this fails,then you need a service manual,and
check out the circuit description for the HV circuitry.The worst thing
would be a bad Z-axis hybrid IC;not made any more,not available new,just
from parts scopes.

--
Jim Yanik,NRA member
remove null to contact me

 

[Jim Yanik]

Grant Erwin <grantNOSPAM@kirkland.net> wrote in
news:vgrvk42uvrbo5e@corp.supernews.com:

Tweezing the astigmatism pot did actually help quite a bit. It's now
probably usable. I was just looking at the DC traces and the
lettering. This scope was shipped without proper (original) packing
material and it may have just bonked the front panel pots a little.

My big concern is if the CRT is gassy - that is a killer when buying
old Tek scopes. Even when you could get replacements they would cost
as much as adding a room on your house!

I've heard that on 2215 scopes there is a resistor string focus
setting network which drifts. I've looked at the schematic for
the focus control electronics on the 24XX scopes and it is an
actual DC amplifier. I don't think this is a resistor drift issue.

As I do have a parts scope available, I do also have the option to
swap the high voltage boards. I don't know if that would cause the
scope to go out of calibration, however.

Grant Erwin
Kirkland, Washington

I've seen some of the small value ceramic tubular caps cause focus/astig
problems.Leaky or shorted caps.
This scope has dynamic focus tracking(with intensity changes).
If you do swap the HV boards,recalibration should be done.

--
Jim Yanik,NRA member
remove null to contact me