Oscilloscope voltage range readout is acting strange

[bonxer]

I've got a Tektronix 2212 that's quite old, and I'm using the cheapy hooks-to-BNC cables that came with my EE kit years ago. Anyway, the on-screen readout for voltage is reading multiple times the actual voltage. While I have the scope set to 5 volts/div, and connect a test signal of +5v DC source, I get the expected straight line. But the readout will sometimes say 5v, then it will change to say 50v. It will alternate between 5 and 50. It does the same when I'm viewing an RS-232 signal also. Although the actual waveform never deforms, I am concerned about its readout. At one point tonight it actually displayed 0.5kV. :shock: Turning the unit off for a few minutes and then back on solved the problem. It is now displaying all units and measures correctly. Any idea what causes this, or if this is a sign of an expensive paperweight in my near future?

 

[zevon8]

Maybe your scope has the BNC's with the contact ring around them that tells the scope what type of lead is connected? There could be a problem with that connection or the related circuitry?

 

[chemelec]

You May have Dirty Switches or Potentiometers, Causing them to Make or Break Contact Intermittantly.

This Happend to me on my B&K Scope.

Try Wiggling the "Volt Per Div" Control and The Adjustable Pot., when it Goes Large and see if it Returns to Normal Size.

If you find this is what is Happening, Get a Can of Control Cleaner. Take the Scope apart and Spray these controls.

Hope This Helps......Gary