On Monday, November 19, 2012 8:20:05 AM UTC-8, wrote:

I have a Tek 2246 ModA which has a slight but annoying problem:

If I leave the scope off for some time, more than a couple hours, when I turn it back on, channel 1 is deflected off screen, below it.

All other channels are there and appear fine, but not channel 1.

Then after a couple minutes it comes back and everything works fine then.

The most likely reason for this, is a power supply sequencing problem.
If it's only channel 1, there's possibly an RC filter in a channel one
supply that has either a faulty resistor (high value) or faulty capacitor
(leakage current too high). It could even be a shorted capacitor
that heats up and behaves better (but that isn't as good as a working capacitor).

It's also possible that offset adjustments of all your channels run off a
highly regulated reference supply, and that secondary supply is
slow coming up (but other channels have a smaller adjustment, so show
less effect).