Do not do anything.
There is one beam.? It has to be "borrowed" to write the readouts.
There are two ways:
1) Borrow the beam when it's needed.? This chops tiny holes in the trace.? it's going to be obvious at some sweep speeds, but will work on slow sweeps.
2) refresh the readouts on the sweep retrace.? This eliminates the "noise" but for slow sweep speeds, you will get a flickering readout.
There's generally a switch on the readout board to control this behavior.
Harvey
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On 12/30/2021 10:14 AM, n4buq wrote:
When displaying a sine-wave where several cycles/division are present, when the READOUT is switched on, there is noticeable "noise" (for lack of a better definition) in the trace. It appears as tiny blank spots in the trace that move rapidly along the trace. The noise is not in sync with the triggering and appears at many points along the trace. Switching the readout off stops the effect.
The power supply has fresh filter caps as well as the horizontal board and the HV board so I don't think this is PS ripple and more likely digital noise from the READOUT circuitry but that's just a guess.
I've looked for places in the READOUT board and/or interface board where there might be bypass filtering components that might have been designed to eliminate this but I don't see anything. I do note that switching on the READOUT connects it to the +15V rail and possibly that's the source of the noise.
I've mostly observed this with sine-waves but it might be present with other waveforms. As a side note, with mostly square-waves, with the GRATICULE ILLUMINATION turned up, I can see a much smaller presentation of similar noise in the trace. This is much less noticeable but could be related.
Any ideas what I can look for as a cause for this?
Thanks,
Barry - N4BUQ
