Re: A 2465 teaser...

Chuck Harris
 

When I first got the scope, it was good, but as I recall,
the fuzz just slowly progressed until it was there always.

That seemed like a capacitor problem, so I started there.

I removed the A1 board to do the capacitor replacement,
and I put all of the screws back myself. They are properly
tightened. That act alone should have refreshed all of the
ground contacts.

The delay line on the 2465 is soldered onto the back of
the A1 board. It doesn't use the little socket pins like
the 465/475 family does.

There is no sensitivity to prodding or smacking the scope
around.

Putting a jumper between CH3/4 and CH1/2 had no effect.

An additional clue is the leading hook's decay curve changes
slope with sweep speed, but the scope will not trigger on
this signal, nor on any of the random grass that appears on
the trace. That indicates that it is getting injected after
the trigger pickoff.

I am pretty certain it has something to do with the display
readout logic.

-Chuck Harris

edbreya@... [TekScopes] wrote:

You may want to check all readily accessible hardware mounting and grounding, particularly around the delay line. If the hooks are constant, then they must be leaking into the circuit past the front-end, and somehow localized so some parts are not affected. The one thing that is commonest to all sections and operations is the grounding. Check that all screws are tightened up snug (and that none are missing), and jiggle things around to see if the symptoms can be aggravated.

To see if you've got some kind of ground loops at the front, jump the apparently unaffected CH3 and CH4 inputs to the CH1 and CH2 - it's easy to just use BNC cables for this.

Ed

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