Sick Scope
 

My Tek 466 scope decided to misbehave. It will not display the horizontal
beam unless I press the beam finder. When I do it displays whatever I'm
looking at(eg: 7 Mhz sine wave) properly.
I'm quite familiar with this scope, but possibly doing something stupid.
Does anyone have any idea as to what the problem could be?
Thanks in advance for any light you can shed on the problem.

Laurie

Laurie:

There are really several possible problems you may be encountering.
Positioning is one, another may be gain...

Beam finder centers the display so you can see you have a trace active. In
most models, it also temporarily switches the scope to auto trigger.

Most likely, you have the horizontal or vertical position maladjusted to put
the display way off the screen... Try centering the horizontal and vertical
position controls and see if you can see the trace.

If you set the trigger to Auto, you should see a trace on the display even if
there is no signal applied. Also, when you press the beam finder, if you
watch closely, you may notice which direction the displayed waveform came
from, or the direction it goes when you release the beam finder button. This
can give you an idea of which of the position controls you need to adjust.

If you have the position controls centered and the trace isn't somewhere near
center, check the DC/AC signal switch. If you have it set to AC, it should
be centered if the display position controls are somewhere near centered. If
the input signal is DC coupled, and there is a significant DC offset to the
signal, it can be off screen. Changing the coupling to AC will help to center
the trace on the display.

Gain could also be a problem. If you have the vertical gain set too high,
even if the display is centered, the trace is spread out so far vertically
that it can be nearly invisible.

Still no joy?
To set the scope to a known state, set Coupling to AC, center the horizontal
position controls, and set the trigger to auto. Turn up the display
brightness (not the graticule illumination) and you should see a single
horizontal line (trace) somewhere near the vertical center of the display.
Add an input signal and you should see a change in the trace. Adjusting the
time base and trigger level should allow resolving the trace to a
stable display.

Nearly everyone has lost a trace in the history of their scope use, been
there, done that myself a time or two, especially when in a hurry....

--Rick AH7H

Laurie Landry wrote:

My Tek 466 scope decided to misbehave. It will not display the horizontal
beam unless I press the beam finder. When I do it displays whatever I'm
looking at(eg: 7 Mhz sine wave) properly.
I'm quite familiar with this scope, but possibly doing something stupid.
Does anyone have any idea as to what the problem could be?
Thanks in advance for any light you can shed on the problem.

Laurie

Laurie:

There are really several possible problems you may be encountering.
Positioning is one, another may be gain...

Beam finder centers the display so you can see you have a trace active. In
most models, it also temporarily switches the scope to auto trigger.

Most likely, you have the horizontal or vertical position maladjusted to put
the display way off the screen... Try centering the horizontal and vertical
position controls and see if you can see the trace.

If you set the trigger to Auto, you should see a trace on the display even if
there is no signal applied. Also, when you press the beam finder, if you
watch closely, you may notice which direction the displayed waveform came
from, or the direction it goes when you release the beam finder button. This
can give you an idea of which of the position controls you need to adjust.

If you have the position controls centered and the trace isn't somewhere near
center, check the DC/AC signal switch. If you have it set to AC, it should
be centered if the display position controls are somewhere near centered. If
the input signal is DC coupled, and there is a significant DC offset to the
signal, it can be off screen. Changing the coupling to AC will help to center
the trace on the display.

Gain could also be a problem. If you have the vertical gain set too high,
even if the display is centered, the trace is spread out so far vertically
that it can be nearly invisible.

Still no joy?
To set the scope to a known state, set Coupling to AC, center the horizontal
position controls, and set the trigger to auto. Turn up the display
brightness (not the graticule illumination) and you should see a single
horizontal line (trace) somewhere near the vertical center of the display.
Add an input signal and you should see a change in the trace. Adjusting the
time base and trigger level should allow resolving the trace to a
stable display.

Nearly everyone has lost a trace in the history of their scope use, been
there, done that myself a time or two, especially when in a hurry....

--Rick AH7H

Laurie Landry wrote:

My Tek 466 scope decided to misbehave. It will not display the horizontal
beam unless I press the beam finder. When I do it displays whatever I'm
looking at(eg: 7 Mhz sine wave) properly.
I'm quite familiar with this scope, but possibly doing something stupid.
Does anyone have any idea as to what the problem could be?
Thanks in advance for any light you can shed on the problem.

Laurie

I just finished repairing my 465 scope that had a similar problem. When powered up the trace would appear off
the left hand side of the screen. Turned out to be bad filter caps in the +5v and -8v supplies. Check the
supply voltages at the TPs, if 2v or more less that what it should be then replace the caps.
After looking at some of the Tek newsgroups I gather that bad filter caps are a common problem with Tektronix
scopes.

Richard WB8KRN


"Laurie Landry" wrote in message ...
My Tek 466 scope decided to misbehave. It will not display the horizontal
beam unless I press the beam finder. When I do it displays whatever I'm
looking at(eg: 7 Mhz sine wave) properly.
I'm quite familiar with this scope, but possibly doing something stupid.
Does anyone have any idea as to what the problem could be?
Thanks in advance for any light you can shed on the problem.

Laurie

I just finished repairing my 465 scope that had a similar problem. When powered up the trace would appear off
the left hand side of the screen. Turned out to be bad filter caps in the +5v and -8v supplies. Check the
supply voltages at the TPs, if 2v or more less that what it should be then replace the caps.
After looking at some of the Tek newsgroups I gather that bad filter caps are a common problem with Tektronix
scopes.

Richard WB8KRN


"Laurie Landry" wrote in message ...
My Tek 466 scope decided to misbehave. It will not display the horizontal
beam unless I press the beam finder. When I do it displays whatever I'm
looking at(eg: 7 Mhz sine wave) properly.
I'm quite familiar with this scope, but possibly doing something stupid.
Does anyone have any idea as to what the problem could be?
Thanks in advance for any light you can shed on the problem.

Laurie

Rick & Joe,
Thanks for your suggestions, however, all of your mentioned items have
been checked, and I am quite confident that the problem lies inside the box.
I now have a 333 page service manual...that unfortunately is more oriented
towards callibration than troubleshooting...but may lead to some useful
information.

Laurie

Rick & Joe,
Thanks for your suggestions, however, all of your mentioned items have
been checked, and I am quite confident that the problem lies inside the box.
I now have a 333 page service manual...that unfortunately is more oriented
towards callibration than troubleshooting...but may lead to some useful
information.

Laurie

Richard,
I believe that you are on target. I will try to find the TPs and verify
the voltages.
You mention Tek newsgroups. Can you tell me their location.
So far, they have eluded my searches.
Thank you very much for your suggestion.

Laurie

Richard,
I believe that you are on target. I will try to find the TPs and verify
the voltages.
You mention Tek newsgroups. Can you tell me their location.
So far, they have eluded my searches.
Thank you very much for your suggestion.

Laurie

Laurie,
Here is one group on yahoo, http://groups.yahoo.com/group/TekSco...guid=145910120
Another is the newsgroup, sci.electronics.repair, this group covers everything under the sun.
I would tell you were to look but the 465 is different than the 466. Mine were on the "interface board"
which is located on the bottom of the scope, they are pins with eyelets in the ends. Voltage should be marked
on the pcb next to the test point pin.
Richard WB8KRN


"Laurie Landry" wrote in message ...
Richard,
I believe that you are on target. I will try to find the TPs and verify
the voltages.
You mention Tek newsgroups. Can you tell me their location.
So far, they have eluded my searches.
Thank you very much for your suggestion.

Laurie