Re: 2215 avoiding future CRT damage

Vincent Trouilliez
 

On Fri, Jul 6, 2018 at 10:35 pm, John Kolb wrote:
The hold-off circuit introduces a delay between one sweep cycle and the next.
Thus the longer the delay, the less often the sweeps occur, which affects the
brightness. If the trace is bright with minimum hold-off, you should be in
good shape.
Thanks a lot John, in just a couple lines you managed to make it all limpid ! :-)

So looks like the Hold-off feature can be used to "select"/pick a particular event in a complex waveform. I now understand why someone advised me to fiddle with hold-off when I was trying to get a clear picture of the switched currents in the inverter of the SMSP of my 2232 scope, which I was fixing. There was a "current sense" resistor which was common to both windings, so I conveniently used it. Of course that meant that I would see the switched current of both windings on the same trace, "interleaved".

Without hold-off, the scope would trigger on both windings indistinctly, hence superimposing them on top of each other. Since the two currents did not have exactly the same amplitude, on the screen I would see a "double" waveform, as if the trace was unstable, which it was not then, just the two currents being "stacked" on one another. When I fiddled with hold-off I could get rid of the double waveform and "select" which of the two currents I wanted to see, and have only that one on the screen. Was great ! :-)

Sorry for the rambling/thinking out loud, but I like it so much when someone with just a few words can clarify something that's been obscure for so long ! ^^

Thanks :-)

Anyway, to get back on topic : looks like my CRT is not worn out, that's a big relief indeed...



Vincent Trouilliez

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