weird Tek scope

Sounds broken. Has it always "worked" this way? Is it still under waranty?

I has always been weird triggering, but I just figured out the actual behavior. It's out of waranty, but it sure looks like a software bug to me, not a real failure.

Perhaps there is nothing to trigger on and setting the trigger level to 3.6V makes it trigger on crosstalk between some circuits.

Quite possibly. Any firmware updates that you haven't installed?

What did TEK customer service say when you asked them? There's a good place for questions of this type:

Don't know if it's still relevant, but the TDS540 series used one D/A converter and a bunch of sample/holds to set all the adjustable levels in the front end. It took very little leakage, usually supplied by electrolyte from leaky caps on the circuit board, to significantly affect the output of the S/H circuits. Possible that AC coupling lets the leakage path control the levels, while DC shunts the leakage to ground.

An interesting experiment might be to input a signal barely large enough to trigger, then switch trigger slope to see it it triggers in the same place.

Is that you Skybuck Flying?

It's worse than that. I forget which one it is (a DPO or MSO something, might be the 2024), but sometimes the trigger level is completely offset. Graphically and (apparently) electrically. Suppose you have a 1Vp-p signal, 500mV/div, and you adjust the trigger level to 0V. Nothing happens, just untriggered AUTO. Some days it might trigger at, say, -1.5V: the triangle arrow "trigger level" indicator isn't *anywhere near* the waveform being displayed! Not all channels have the same offset, at any given time. Some read correct, some do this. It's stupid.

I'm getting pretty confident that, somewhere in the 80s to 90s, Tek simply gave away all their credibility, at least with regards to their low end models. Agilent has won. Next time I'm shopping for a scope, I might just forego eBay and buy a brand new Agilent, off the shelf.

My TDS460 (circa 1992 was it?) seems to work okay, the UI is just slow.

Tim

-- Deep Friar: a very philosophical monk. Website:

The Rigol stuff is pretty good. The last two scopes that we bought were a 1 GHz Rigol and a 6 Ghz LeCroy, both 4 channels.

Color digital scopes rock. Those old toob scopes confuse me... everything is green!