Topics

Tektronix 2245a Flickering Trace

William Schuler
 

Hey guys, newbie here. First of all I want to say thanks for what a great resource this place is! Made my donation two days ago.

I have a Tektronix 2245a, which I bought about a year ago. This is my first scope, and I’m still learning how to use it. I have replaced all the power supply capacitors, and all the voltages test out OK., and the unit runs OK when I first power it on. After about 10 minutes though, I start to get ghost traces and a jumpy, flickering image. Here is a link to a video I made of the unit. https://youtu.be/j6Dqke1CIRE

It is usable for what I do, which is just viewing a signal after it’s gone through a tube amp, but I would like to track down the issue. Any suggestions on where to look?

Thanks everyone, Bill

Panos
 

Hi Bill,
Is this disappear if you will use one of the freq rejection filters, or hold off setting?


Panos

KB6NAX
 

Hi Bill,

Sounds like Panos has a clue. Switch in the 20 MHz bandwidth filter to see if the erratic triggering stops or lessens. Too much bandwidth can be a problem in a noisy environment. If the triggering in 20 MHz mode still acts up there's something noisy in the triggering circuits.

Arden

-----Original Message-----
From: guitardad1967@...
Sent: Thursday, January 02, 2020 5:58 AM
To: TekScopes@groups.io
Subject: [TekScopes] Tektronix 2245a Flickering Trace

Hey guys, newbie here. First of all I want to say thanks for what a great resource this place is! Made my donation two days ago.

I have a Tektronix 2245a, which I bought about a year ago. This is my first scope, and I’m still learning how to use it. I have replaced all the power supply capacitors, and all the voltages test out OK., and the unit runs OK when I first power it on. After about 10 minutes though, I start to get ghost traces and a jumpy, flickering image. Here is a link to a video I made of the unit. https://youtu.be/j6Dqke1CIRE

It is usable for what I do, which is just viewing a signal after it’s gone through a tube amp, but I would like to track down the issue. Any suggestions on where to look?

Thanks everyone, Bill

William Schuler
 

Thanks Arden, I’ll give that a whirl this weekend.

On Thu, Jan 2, 2020 at 2:04 PM KB6NAX <gumbear@...> wrote:

Hi Bill,

Sounds like Panos has a clue. Switch in the 20 MHz bandwidth filter to
see
if the erratic triggering stops or lessens. Too much bandwidth can be a
problem in a noisy environment. If the triggering in 20 MHz mode still
acts
up there's something noisy in the triggering circuits.

Arden

-----Original Message-----
From: guitardad1967@...
Sent: Thursday, January 02, 2020 5:58 AM
To: TekScopes@groups.io
Subject: [TekScopes] Tektronix 2245a Flickering Trace

Hey guys, newbie here. First of all I want to say thanks for what a great
resource this place is! Made my donation two days ago.

I have a Tektronix 2245a, which I bought about a year ago. This is my
first
scope, and I’m still learning how to use it. I have replaced all the power
supply capacitors, and all the voltages test out OK., and the unit runs OK
when I first power it on. After about 10 minutes though, I start to get
ghost traces and a jumpy, flickering image. Here is a link to a video I
made
of the unit. https://youtu.be/j6Dqke1CIRE

It is usable for what I do, which is just viewing a signal after it’s gone
through a tube amp, but I would like to track down the issue. Any
suggestions on where to look?

Thanks everyone, Bill






Siggi
 

Hey Bill,

I think it's safe to say that you have more than just a triggering issue,
as your OSD (on-screen display) is jumping around as well as the traces
(see e.g. around here https://youtu.be/j6Dqke1CIRE?t=74). This could be as
simple as a marginally plugged-in connector somewhere, but you should be
looking at points common to the OSD and sweeps. This includes power
supplies and e.g. the horizontal amplifier. Your vertical appears
unaffected, however.
If you haven't read this:
https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf already,
you may want to take a gander. Do you have a second scope you could turn on
your 2245A?

Siggi

On Thu, Jan 2, 2020 at 8:23 PM William Schuler <guitardad1967@...>
wrote:

Thanks Arden, I’ll give that a whirl this weekend.

On Thu, Jan 2, 2020 at 2:04 PM KB6NAX <gumbear@...> wrote:

Hi Bill,

Sounds like Panos has a clue. Switch in the 20 MHz bandwidth filter to
see
if the erratic triggering stops or lessens. Too much bandwidth can be a
problem in a noisy environment. If the triggering in 20 MHz mode still
acts
up there's something noisy in the triggering circuits.

Arden

-----Original Message-----
From: guitardad1967@...
Sent: Thursday, January 02, 2020 5:58 AM
To: TekScopes@groups.io
Subject: [TekScopes] Tektronix 2245a Flickering Trace

Hey guys, newbie here. First of all I want to say thanks for what a great
resource this place is! Made my donation two days ago.

I have a Tektronix 2245a, which I bought about a year ago. This is my
first
scope, and I’m still learning how to use it. I have replaced all the
power
supply capacitors, and all the voltages test out OK., and the unit runs
OK
when I first power it on. After about 10 minutes though, I start to get
ghost traces and a jumpy, flickering image. Here is a link to a video I
made
of the unit. https://youtu.be/j6Dqke1CIRE

It is usable for what I do, which is just viewing a signal after it’s
gone
through a tube amp, but I would like to track down the issue. Any
suggestions on where to look?

Thanks everyone, Bill








KB6NAX
 

Yup, I have to agree with Siggi. The "OSD," meaning the vertical
sensitivity callout in the lower left hand corner and the sweep time in the
lower right hand corner also are jumping sideways along with the
sine wave. So the jitter is occurring in the horizontal amplifier chain, not
the triggering circuit. With power off, carefully reseat anything that plugs in.
Don't slip up and plug anything back in wrong that you pulled out - no bent
pins, etc.

Arden


I think it's safe to say that you have more than just a triggering issue,
as your OSD (on-screen display) is jumping around as well as the traces
(see e.g. around here https://youtu.be/j6Dqke1CIRE?t=74). This could be as
simple as a marginally plugged-in connector somewhere, but you should be
looking at points common to the OSD and sweeps. This includes power
supplies and e.g. the horizontal amplifier. Your vertical appears
unaffected, however.
If you haven't read this:
https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf already,
you may want to take a gander. Do you have a second scope you could turn on
your 2245A?

Siggi <

William Schuler
 

Thanks for narrowing it down guys. I will look into it this weekend. I
could take it over to my buddies house who has a scope...

On Thu, Jan 2, 2020 at 8:54 PM KB6NAX <gumbear@...> wrote:

Yup, I have to agree with Siggi. The "OSD," meaning the vertical
sensitivity callout in the lower left hand corner and the sweep time in the
lower right hand corner also are jumping sideways along with the
sine wave. So the jitter is occurring in the horizontal amplifier chain,
not
the triggering circuit. With power off, carefully reseat anything that
plugs in.
Don't slip up and plug anything back in wrong that you pulled out - no bent
pins, etc.

Arden


I think it's safe to say that you have more than just a triggering issue,
as your OSD (on-screen display) is jumping around as well as the traces
(see e.g. around here https://youtu.be/j6Dqke1CIRE?t=74). This could be as
simple as a marginally plugged-in connector somewhere, but you should be
looking at points common to the OSD and sweeps. This includes power
supplies and e.g. the horizontal amplifier. Your vertical appears
unaffected, however.
If you haven't read this:
https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf
already,
you may want to take a gander. Do you have a second scope you could turn on
your 2245A?

Siggi <




William Schuler
 

“Do you have a second scope you could turn on
your 2245A?

Siggi”

That makes me wonder – can you use a mostly functional scope to diagnose
itself? Or could that be catastrophic, like creating tears in the
time/space continuum when messing around with time machines? ; )

If it comes to it my friend has a scope for use.

On Thu, Jan 2, 2020 at 11:22 PM William Schuler via Groups.Io
<guitardad1967=gmail.com@groups.io> wrote:

Thanks for narrowing it down guys. I will look into it this weekend. I
could take it over to my buddies house who has a scope...

On Thu, Jan 2, 2020 at 8:54 PM KB6NAX <gumbear@...> wrote:

Yup, I have to agree with Siggi. The "OSD," meaning the vertical
sensitivity callout in the lower left hand corner and the sweep time in
the
lower right hand corner also are jumping sideways along with the
sine wave. So the jitter is occurring in the horizontal amplifier chain,
not
the triggering circuit. With power off, carefully reseat anything that
plugs in.
Don't slip up and plug anything back in wrong that you pulled out - no
bent
pins, etc.

Arden


I think it's safe to say that you have more than just a triggering
issue,
as your OSD (on-screen display) is jumping around as well as the traces
(see e.g. around here https://youtu.be/j6Dqke1CIRE?t=74). This could be
as
simple as a marginally plugged-in connector somewhere, but you should be
looking at points common to the OSD and sweeps. This includes power
supplies and e.g. the horizontal amplifier. Your vertical appears
unaffected, however.
If you haven't read this:
https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf
already,
you may want to take a gander. Do you have a second scope you could turn
on
your 2245A?

Siggi <






Panos
 

On Sat, Jan 4, 2020 at 02:59 PM, William Schuler wrote:

That makes me wonder – can you use a mostly functional scope to diagnose
itself?
I think that already I see the Star Trek to arriving as to save the earth after this!!!

Siggi
 

On Sat, Jan 4, 2020 at 8:00 AM William Schuler <guitardad1967@...>
wrote:

That makes me wonder – can you use a mostly functional scope to diagnose
itself?

I guess it depends, though a large section of this document (
https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf) is
about "Front-Panel Diagnosis" which largely interrogates the instrument
about its own faults. You can - to a point - use a scope to look at its own
power supply ripple and the like, and *some* of its internal state, like
some portion of the sweep ramp(s). I guess it can be hard to know what to
believe when the instrument itself is faulty.
This scope also has a service mode with some self-diagnosis capability. You
can get the service manual from here (http://w140.com/tekwiki/wiki/2245),
see page 6-10 for the service menu.

Also note that every scope has two built-in "signal sources"; the
calibrator and GND coupling, and most scopes have an additional trigger
signal which is the line. You can also think of AUTO trigger mode and the
holdoff as trigger signals. Then there's X/Y mode, which allows you to
introduce a calibrated signal to the horizontal circuitry. In your case, it
might be interesting to inject DC on the X, and e.g. a sine or triangle
wave on the Y. It might also be interesting to play with line triggering to
see whether the glitching is line-synchronous, which could happen if e.g.
you have excessive line ripple on a supply ... time passes ... these scopes
have a switch-mode power supply, so more likely power supply noise or
ripple will be at the switching frequency.

If it comes to it my friend has a scope for use.


That'll certainly be an easier way to go :). If you poke around in the
power supply, be very, very careful, as everything except the final
low-voltage supplies are line-referenced.

Good luck and much fun,
Siggi

Panos
 

I have read enough service manuals for the oscilloscopes, and till today I didn't find any of them to mention, that someone can use the same faulty scope (partially or totally) to repair his self.
But as always we can hope for something like that. After all, don't they say that hope dies always last? :-)

In my opinion if you have time to play then do it by that way. But if you want really to repair it, then proceed it with another oscilloscope.

William Schuler
 

Exactly!

On Sat, Jan 4, 2020 at 9:39 AM Panos <sadosp@...> wrote:

On Sat, Jan 4, 2020 at 02:59 PM, William Schuler wrote:

That makes me wonder – can you use a mostly functional scope to diagnose
itself?
I think that already I see the Star Trek to arriving as to save the earth
after this!!!



William Schuler
 

I am in no hurry, so I will give it a try just for fun. It would be
interesting to compare results with my buddy’s functional scope. Now to
figure out exactly where that horizontal amplifier is....

On Sat, Jan 4, 2020 at 2:29 PM Panos <sadosp@...> wrote:

I have read enough service manuals for the oscilloscopes, and till today I
didn't find any of them to mention, that someone can use the same faulty
scope (partially or totally) to repair his self.
But as always we can hope for something like that. After all, don't they
say that hope dies always last? :-)

In my opinion if you have time to play then do it by that way. But if
you want really to repair it, then proceed it with another oscilloscope.



Siggi
 

On Sat, Jan 4, 2020 at 8:13 PM William Schuler <guitardad1967@...>
wrote:

I am in no hurry, so I will give it a try just for fun. It would be
interesting to compare results with my buddy’s functional scope.

Hmmm, you already see the output of the horizontal amplifier - that's what
your CRT shows.
The only thing is that your horizontal output (
https://youtu.be/8dzxGlcErUo?t=10) is differential. By comparing both
sides, you'd be able to see whether this is due to one side pulling or both
- it's a data point at least. I'd bet that you'll find your problem
elsewhere than in the horizontal amp, though. I'm betting on power
supplies, as that's where ~90% of all trouble happens. Is the fan working
OK?
In any case, while I often^Wsometimes miss the most direct way to figure
out what's up, I find the detours are more than worth their while for the
learnin'.


Now to
figure out exactly where that horizontal amplifier is....
You have the service manual (
http://www.ko4bb.com/manuals/download.php?file=Tektronix/Tektronix_-_2245A/Tektronix_2245A_Oscilloscope_Service_Manual.pdf
)?

Have fun!
Siggi

Harvey White
 

There are some tests you can do with a partially working scope, but you are going to be very limited.

1) assuming horizontal sweep problems, you use an external ramp or the "other" sweep if you have a dual sweep model.

2) if you have a horizontal amplifier problem, using the scope in XY mode, even with the calibrator, can give you some idea of whether or not it's the sweep or the amplifier.

3) if you have a dual channel scope, you can use a working channel to debug the separate part of the vertical amplifier

These generally end up being go/no-go tests and are somewhat crude.

Function generators can make a very crude horizontal sweep.  If they're gated, then a gated ramp might work as a sweep.

Very crude, but better than nothing.

Generally, unless you have a scope specifically designed for self diagnosis, you're better off with another, completely working, scope.

Even then, a scope designed for self diagnosis makes certain assumptions about what's working, especially once you get past the "is the CPU working...."

Harvey

On 1/4/2020 4:29 PM, Panos wrote:
I have read enough service manuals for the oscilloscopes, and till today I didn't find any of them to mention, that someone can use the same faulty scope (partially or totally) to repair his self.
But as always we can hope for something like that. After all, don't they say that hope dies always last? :-)

In my opinion if you have time to play then do it by that way. But if you want really to repair it, then proceed it with another oscilloscope.


William Schuler
 

Thanks Siggy, I appreciate the pointers. Nice “outer limits“ clip as well!

BTW, the fan runs fine.

On Sat, Jan 4, 2020 at 6:45 PM Siggi <siggi@...> wrote:

On Sat, Jan 4, 2020 at 8:13 PM William Schuler <guitardad1967@...>
wrote:

I am in no hurry, so I will give it a try just for fun. It would be
interesting to compare results with my buddy’s functional scope.

Hmmm, you already see the output of the horizontal amplifier - that's what
your CRT shows.
The only thing is that your horizontal output (
https://youtu.be/8dzxGlcErUo?t=10) is differential. By comparing both
sides, you'd be able to see whether this is due to one side pulling or both
- it's a data point at least. I'd bet that you'll find your problem
elsewhere than in the horizontal amp, though. I'm betting on power
supplies, as that's where ~90% of all trouble happens. Is the fan working
OK?
In any case, while I often^Wsometimes miss the most direct way to figure
out what's up, I find the detours are more than worth their while for the
learnin'.


Now to
figure out exactly where that horizontal amplifier is....
You have the service manual (

http://www.ko4bb.com/manuals/download.php?file=Tektronix/Tektronix_-_2245A/Tektronix_2245A_Oscilloscope_Service_Manual.pdf
)?

Have fun!
Siggi



William Schuler
 

Thanks Harvey, going through some family things right now, but hopefully I
can get to looking at the scope this weekend.

On Sun, Jan 5, 2020 at 9:35 PM Harvey White <madyn@...> wrote:

There are some tests you can do with a partially working scope, but you
are going to be very limited.

1) assuming horizontal sweep problems, you use an external ramp or the
"other" sweep if you have a dual sweep model.

2) if you have a horizontal amplifier problem, using the scope in XY
mode, even with the calibrator, can give you some idea of whether or not
it's the sweep or the amplifier.

3) if you have a dual channel scope, you can use a working channel to
debug the separate part of the vertical amplifier

These generally end up being go/no-go tests and are somewhat crude.

Function generators can make a very crude horizontal sweep. If they're
gated, then a gated ramp might work as a sweep.

Very crude, but better than nothing.

Generally, unless you have a scope specifically designed for self
diagnosis, you're better off with another, completely working, scope.

Even then, a scope designed for self diagnosis makes certain assumptions
about what's working, especially once you get past the "is the CPU
working...."

Harvey


On 1/4/2020 4:29 PM, Panos wrote:
I have read enough service manuals for the oscilloscopes, and till today
I didn't find any of them to mention, that someone can use the same faulty
scope (partially or totally) to repair his self.
But as always we can hope for something like that. After all, don't
they say that hope dies always last? :-)

In my opinion if you have time to play then do it by that way. But if
you want really to repair it, then proceed it with another oscilloscope.





battyhugh
 

Telonics 2003

I was hoping that the seller (of the manual) would link me with the buyer - no luck. So does some kind person had the manual for the earlier model - (or does anyone still have a 2003 manual loitering in a cupboard?? (or the old 3 pin plug?).

I'd hate to scrap it.

Cheers

hugh

Tony Fleming
 

First of all Harvey, Happy New Year 2020 and wishes of lots of health and
great ELECTRONS in your life!
If it wasn't for you, my scope would not work, so I trust you and wish you
are my neighbor!
Anyway, thanks for helping everyone here, including me. ( tonysfun.com and
click on MY VIDEOS to see how micro-knowledge functions in my very small
brain! ... ha ha ha)

Lastly, I wish you all HAPPY NEW YEAR 2020 and POSITIVE ELECTRON'S in your
life and scopes!

Tony

On Sun, Jan 5, 2020 at 10:35 PM Harvey White <madyn@...> wrote:

There are some tests you can do with a partially working scope, but you
are going to be very limited.

1) assuming horizontal sweep problems, you use an external ramp or the
"other" sweep if you have a dual sweep model.

2) if you have a horizontal amplifier problem, using the scope in XY
mode, even with the calibrator, can give you some idea of whether or not
it's the sweep or the amplifier.

3) if you have a dual channel scope, you can use a working channel to
debug the separate part of the vertical amplifier

These generally end up being go/no-go tests and are somewhat crude.

Function generators can make a very crude horizontal sweep. If they're
gated, then a gated ramp might work as a sweep.

Very crude, but better than nothing.

Generally, unless you have a scope specifically designed for self
diagnosis, you're better off with another, completely working, scope.

Even then, a scope designed for self diagnosis makes certain assumptions
about what's working, especially once you get past the "is the CPU
working...."

Harvey


On 1/4/2020 4:29 PM, Panos wrote:
I have read enough service manuals for the oscilloscopes, and till today
I didn't find any of them to mention, that someone can use the same faulty
scope (partially or totally) to repair his self.
But as always we can hope for something like that. After all, don't
they say that hope dies always last? :-)

In my opinion if you have time to play then do it by that way. But if
you want really to repair it, then proceed it with another oscilloscope.





William Schuler
 

Well I fear the worst... While self diagnosing power supply ripple, I
touched 130 V test point, saw a bright flash on screen, then everything
went black. Unit powers up, LEDs on front light up, relays click, but there
is no display on the screen. The beam find button does nothing. Bummer! I
realized I didn’t have probe on 10 X. Is there any hope you guys?

On Sat, Jan 4, 2020 at 11:27 AM Siggi <siggi@...> wrote:

On Sat, Jan 4, 2020 at 8:00 AM William Schuler <guitardad1967@...>
wrote:

That makes me wonder – can you use a mostly functional scope to diagnose
itself?

I guess it depends, though a large section of this document (
https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf) is
about "Front-Panel Diagnosis" which largely interrogates the instrument
about its own faults. You can - to a point - use a scope to look at its own
power supply ripple and the like, and *some* of its internal state, like
some portion of the sweep ramp(s). I guess it can be hard to know what to
believe when the instrument itself is faulty.
This scope also has a service mode with some self-diagnosis capability. You
can get the service manual from here (http://w140.com/tekwiki/wiki/2245),
see page 6-10 for the service menu.

Also note that every scope has two built-in "signal sources"; the
calibrator and GND coupling, and most scopes have an additional trigger
signal which is the line. You can also think of AUTO trigger mode and the
holdoff as trigger signals. Then there's X/Y mode, which allows you to
introduce a calibrated signal to the horizontal circuitry. In your case, it
might be interesting to inject DC on the X, and e.g. a sine or triangle
wave on the Y. It might also be interesting to play with line triggering to
see whether the glitching is line-synchronous, which could happen if e.g.
you have excessive line ripple on a supply ... time passes ... these scopes
have a switch-mode power supply, so more likely power supply noise or
ripple will be at the switching frequency.

If it comes to it my friend has a scope for use.


That'll certainly be an easier way to go :). If you poke around in the
power supply, be very, very careful, as everything except the final
low-voltage supplies are line-referenced.

Good luck and much fun,
Siggi