Tek 465B scope repair

[uberblitz]

Hello,

I am sort of stumped trying to fix my Tek 465B scope. It was working fine a few weeks ago but has developed some strange issues as of late.

Symptoms:
1. With no inputs I get flat lines on both inputs. However, when I turn on scale illumination I get noise on both channels.
2. When either input is connected to the calibration output, I see two lines being drawn on the square wave.

I have checked the voltage rails on the power supply board, and the +110, +55, +15, +5, and -8 look to be within expected values and are stable.

Any ideas on what I should check?

[grumpydoc]

Power supply lines for voltage and ripple, power supply caps for ESR.

[uberblitz]

Well, I think the issue has a lot to do with my bench fluorescent lights I found that the scope started working right after I turned my lights off. That would explain why I didn't have any issues until a couple of weeks ago with it (that's when I replaced the tubes)

SO, that probably means that the main input caps are getting weak and can't filter out that stuff anymore? I don't have an ESR meter (and my dmm doesn't go up high enough to test their capacitance). Any ideas on how to test them?

[grumpydoc]

You can measure ESR with a sig gen and 'scope - see the notes here. I suspect the difficulty will be that you don't have a 2nd 'scope.

[uberblitz]

I will give that a try. (And I actually have 3 scopes, so it isn't an issue :-)

[ModemHead]

Check the grounding contacts for the outer can, make sure they make good contact.  Also check all the screws around the vertical attenuator modules for tightness and good contact, especially the shields.  The mechanical integrity and grounding around that area is more important than one might think.