[Test-Equipment] Tektronix PS 503A

[David]

As much as I prefer mailman.qth.net, you would probably be better
served asking questions about Tektronix equipment over at
TekScopes at yahoogroups.com or TekScopes2 at yahoogroups.com.

I do not have an experience with any of the TM series oscilloscope
plug-ins but that sounds like a internal power supply problem to me.
If the SC504 is like most other Tektronix oscilloscopes, it has a high
frequency inverter and/or switching regulator which provides the
various internal and CRT operating voltages.  The electrolytic
capacitors may have worn out and be in need of changing.

One easy thing to try is operating it in a different mainframe or a
different set of slots in the same mainframe in the event that the
mainframe power supply is the problem.

Also try using LINE triggering to see if the noise is synchronous to
the AC power line.

On Wed, 26 Sep 2012 15:20:08 -0400, Ray <w4byg at att.net> wrote:

>The current dialog above brings up a question for me.
>
>I have a very nice SC-504 80 MHz scope mounted in the right hand 2 slots 
>of a TM-504 .  It has worked well for me for years.
>
>However, I just turned it on and the scope trace will not resolve to a 
>fine line vertically as it should.  It seems to be internally modulated 
>by about 3/4 of a division of vertical noise across the horizontal trace.
>
>The focus control has no effect on the problem.  It does not appear to 
>be any sort of an external RFI, etc., as inserting the internal filters 
>or grounding the input, doesn't change the displayed noise. The noisy 
>trace problem persists if connected to the cal test point.  In cal mode, 
>the  top of the square wave has the same erroneous noise.   Changing the 
>vertical sensitivity changes the amplitude square wave display as it 
>should, but does not change the level of the problem noise on the trace. 
>   The noise stays the same amount in all input settings.   I take this 
>to indicate the problem is internal and not external.
>
>The horizontal settings display and trigger OK.  Rotating the 
>seconds/div knob seems to work as it should but does not give any clue 
>as to any time interval or frequency, of the source of the problem.
>
>Before I dig into it, does anyone have any experienced suggestions as to 
>how to track the problem down and repair it?  As a guess, I would think 
>it's a capacitor break down somewhere in the vertical output amplifier 
>circuit, because it's in both vertical channels.
>
>  I have the large extender for TM-500 modules and a photocopy of the 
>manual.  I do not have a small extender board to match the small (other) 
>connector on the back of the scope.  It may not be needed for 
>troubleshooting.
>
>Your attention is appreciated.
>Ray, W4BYG
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