Tektronix TDS 340 help

[aqibi2000]

I’ve scored this scope cheap

And was told it was dead, as it arrived I dissembled and checked all unlit stages for shorts and the input high wattage power resistors


It turned on to my joy, but it’s not working correctly

1) When power is inserted all the buttons illuminate and the screen stays off, I press the power button and the unit boots up and passes all test, yet I cannot turn it off from the same switch?

2) the 2 reference signals are always displayed, how does one turn these off permanently - maybe the Coin cell battery needs replacing

3) the signal is very noisy

I know these can do with RECAP but I’d like to see what other failures may be on the cards

Poor photo looks like it’s a long exposure photo

[Smoky]

The first thing I would do is pop the grille off of the front of the scope. Remove the rubber membrane that holds the carbon contacts for the soft-buttons. Put it in a container of hot water and dish-washing soap. Scrub it with a toothbrush, rinse, and pat it dry.

Look closely at the carbon buttons in the membrane, if you see a silhouette or shadow on them, lightly swipe the face of them with a piece of 2000 grit or higher wet/dry sandpaper to remove the glazing.

Next, take a soft dampened cloth and lightly wipe over the contacts taped to the chassis of the oscilloscope. Don't use alcohol or any other solvent to do this.

The same needs to be done to the membrane behind the front panel board since there are soft-buttons that select/remove the waveforms. I've seen electrolyte eat the traces to the contacts and make the switch inoperable.

[aqibi2000]

I think you’re right. I thought I was powering it up but instead it’s auto booting up after about 30’ seconds of power.

Every button currently works on the front membrane so need to give the power button and ribbons some attention.

Also the noise signal was actual noise over the cables from my function gen ha ha

Thank you I’ll feedback after doing what you suggested to the entire unit