Oscilloscope distorted waveform at edges

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1audio

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Joined 2004
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Having thought about this I would guess that the HV (main accelerator voltage) is low. That will cause the defection to increase and typically the increase is larger at the edges than the center. A failing HV rectifier or some crud could be causing a lot of leakage.
 
BKnut

BKnut

Member
Joined 2021
Cool ohm, Can you take a photo of the CRT plug and the thin rotator discs glued near the CRT plug? I'm thinking magnetic alignment or linearity gain on the horizontal ccts( 1 div OK, 4 div bending) .

Check for CRT shield near the front panel & no loose wires leading to the CRT.


Watch out of high Voltage.
 
Mooly

Mooly

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Joined 2007
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1audio said:
Having thought about this I would guess that the HV (main accelerator voltage) is low. That will cause the defection to increase and typically the increase is larger at the edges than the center. A failing HV rectifier or some crud could be causing a lot of leakage.
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Good thinking. I wonder if altering the brightness up and down shows a change in the problem. Low EHT makes the beam easier to deflect and so if the brightness is whizzed up and down and the image size on screen alters then that points to a problem.

Using the squarewave Cal signal was one reason I wanted to see if the sweep was basically linear and that the markers line up OK. Do they ?

Also thinking aloud and just covering all bases.

Are those two large speaker cabinets I see in the picture? Big unshielded magnets? but then it wouldn't still be OK at low amplitude.

Any change if you turn the scope on its side?
 
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