Were you just in some part of the Service menu ?
For a TDS2k from the Service manual:
1. Power on the oscilloscope.
2. Push the front-panel MEASURE button to access the MEASURE menu.
3. Push the top option button to access the Measure 1 menu.
At step 3, the TDS3K top menu button is "snapshot all measurements" I continued on anyway, but no service menu.
If this was a service menu, odd that it would survive a power cycle.
OK the 3k seems a bit different.
From the TEK wiki site
http://w140.com/tek_tds_3000_series_service.pdfFactory Adjustment Procedure
To perform the factory adjustment procedure, do these steps:
1. Locate the hole that provides access to the CAL switch on the rear panel.
CAL
2. Put the adjustment tool into the CAL switch hole. Push and hold the CAL switch in while you power on the oscilloscope. Release the switch when the oscilloscope shows the power-on message with the oscilloscope graticule in the background.
3. Push the SAVE/RECALL button.
4. Push the Recall Factory Setup screen button.
5. Push the OK Confirm Factory Init screen button to restore factory settings prior to doing the factory calibration.
6. Push the MENU OFF button.
7. Push the UTILITY button.
8. Push the System screen button to select Cal.
9. Push the Factory screen button.
10. Push the OK Do Factory Calibration screen button to start the adjustment process
11. Connect signals from the DC voltage source, leveled sine wave, or fast-rise generator as instructed by the oscilloscope display. After you connect the correct signal, push the OK Do Next Step screen button to continue the
process.
NOTE. The oscilloscope adjusts itself automatically using the reference signal from the DC voltage source, leveled sine wave, or fast-rise generator. There are no manual oscilloscope adjustments that you need to make.
If you make an error, such as connecting the wrong input signal, you can repeat the last step by pushing the Return to Previous Screen screen button.
12. Continue the adjustment process until it is complete. You can abort the process at any time by pushing the MENU OFF button or by changing to a different menu.