Re: 454A With Strange Oscillation


You do get trace interference on the 453 and 454 if you operate the 'scope with the EHT section (aluminium) cover off. Do you have this cover in place?


--- In, David <davidwhess@...> wrote:

The inverter that produces the CRT voltages operates at about 26 kHz
but I do not see any obvious way for it to get into the vertical
signal path.

Did you check the DC supply voltages for 26 kHz ripple? Maybe the
inverter output is getting into them.

I would also check the vertical CRT amplifier to see if both sides of
the differential signal are operating correctly. Is the vertical
calibrated gain what it should be?

On Mon, 24 Dec 2012 04:53:24 -0000, "Mike Harmon" <mharmon@...>

I have a 454A portable scope with a strange problem. Instead of a clean horizontal line, the trace on the scope exhibits a sine wave of approximately 26 kHz. After switching both vertical inputs to ground with no change (the problem appears on both input channels), I began working my way through the vertical preamps and switching circuitry.

All voltages in the scope appear to be right on, and the the signal lines are completely clean all the way to the thick film hybrid vertical output assembly, but the output connections to the deflecting plates show the 26 kHz sine wave where there should be nothing. The offending sinewave has to be introduced in the hybrid assembly or somehow coming from in the CRT itself.

Has anyone ever heard of anything like this? I have a "parts" 454A, but I thought I'd bounce this off the group before I went tearing the vertical amp out of another scope.

Please let me know if you have any words of wisdom or suggestions.

Merry Christmas everybody!
Mike Harmon, WB0LDJ
mharmon at att dot net

Join to automatically receive all group messages.