My 2246 Oscilloscope Quit Working Today - Suggestions

[Jamie Starr]

Guys: I was rearranging my bench today as I installed a new shelf. When I went to test my gear, the scope screen begin flashing like a Christmas tree. Actually it was just the traces. I assumed that I didn’t push the plug all the way into the rear of the unit or perhaps it was loose at the wall power strip. In any case, it appeared to begin working after flashing for about 10 seconds. However, upon closer look, the “uncal” lights now stay lit. I have made sure all the knobs and buttons are in the appropriate positions. I have tried to unplug it in an attempt to reset the unit, but no luck. Ironically, it’s still reads sine waves fine and from what I can tell it works as normal except when I try to use the built-in meter to read the peak to peak voltage, it can’t do because it reads as “uncal.”
I opened the unit and took some reading from power board. Those checked out fine.
Any suggestions on what to do with the unit. I paid $125 for it a year ago. I think repairing it is beyond my skills. The service manual is 300 pages long. I don’t want to put in electronic landfill, but I assume I could buy a brand new digital scope for the price to get it repaired. Suggestions? Thanks

 

[BillWojo]

Go over to the EEVBlog forum. They have a section there that covers repairing test gear. Tex scopes are popular because of the high build quality.

BillWojo

 

[Watthour]

On many Tektronix, the "uncal" indicator will illuminate when the variable volt/division or sweep time controls are not fully returned to the OFF position. Just for the sake of argument, turn on the o-scope, feed a signal and get the waveform display stabilized. Then operate the "VAR" knobs for Volts/Div for each channel and see if the raster changes with the control position. Turn off the variable control for that channel, then switch to the opposite channel for the same checks. Then perform the same kind of check with the "VAR" knob for the sweep time (Sec/Div) control.

It might be that one was inadvertently left on, or that the the switch contacts incorporated in each variable control are a little dirty or oxidized. Some exercise of the controls might help, and cleaning might even be necessary. We see the same thing on function switches and potentiometers in our audio gear all the time, and the 2246 is getting close to that age.

 

[Jamie Starr]

On many Tektronix, the "uncal" indicator will illuminate when the variable volt/division….It might be that one was inadvertently left on, or that the the switch contacts incorporated in each variable control are a little dirty or oxidized. Some exercise of the controls might help, and cleaning might even be necessary. We see the same thing on function switches and potentiometers in our audio gear all the time, and the 2246 is getting close to that age.

Thanks for taking the time to respond. While I had the cover off, I began tapping around on the components to see if anything would change.
After doing that, and making sure all the ribbon connectors were secure, the “uncal” light has gone off and things are working again. Maybe when I was moving the unit around, something came loose. Or again as you said, it could just be the age of the components. In any case, it’s back working now. Thanks again for chiming in.