Re: Another scope 7854

Joe Laffey
 

When this glitch occurs I noticed that the glitch waveform that appears joy for an instant looks like the triggering has the trigger slope inverted from the main waveform.

Cleaning and exercising the slope switch on the time base has no effect (which makes sense since it happens only with channel 2. Actually I will very very occasionally see something with channel 1 as well.

Still searching... I tried some percussive troubleshooting with a chopstick, but couldn't find anyplace where tapping made it better or worse.


--
Joe Laffey

On May 4, 2017, at 9:14 PM, Joe Laffey joe@... [TekScopes] <TekScopes@...> wrote:

The new C375 fixed the gain issues. Thanks again.

I am still having these triggering glitches.

Test waveform is a sine wave. Frequency doesn't seem to matter much.

Triggering off Ch1 is working fine.

Triggering off Ch2 has the occasional glitch.

Trigger off "Mode" (in between Ch1 and Ch2) also has the glitches

Trigger off external trigger is fine.

When the glitch happens I see for a split second an additional waveform out of phase, but the same amplitude.

When I have Ch2 inverted the glitches are much less frequent.

When I set the coupling to DC offset the glitches go away. They are present on AC and DC Coupling.

If I use variable gain on Ch2 and reduce the gain to around 50% or less the issue goes away. (something clipping?)

Trigger slope has no impact.

High frequency reject triggering fixes the issue as well.

I cleaned the trigger source wafer switch, and it seems to be OK with a meter.

I cleaned the cam switches for both volts/div and coupling mode. This did not seem to make much difference. Also, it looks like if this were the problem then D.C. Offset would have the issue as well.

I twiddled R521-- DC balance for Ch2-- back and forth to no avail

I will keep digging around... any insights appreciated.

Thanks.

--
Joe Laffey


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