Tektronix 2215 Help

[Heliman]

I just recently bought a Tektronix 2215 scope. I checked the scope out and everything is calibrated and is very accurate. The problem is when displaying a sine wave below 1 Mhz the display is fine, has good brightness. Putting the scope in XY mode with just a spot on screen it also has good brightness. When you start going over 1 Mhz the trace gets dimmer the higher in frequency it goes. By the time the frequency reaches 25 Mhz you can barely see the trace. Its still accurate just really dim. The intensity control gets really touchy and turning to far to the right or to far to the left and the trace will disappear. Ive checked all the power supply voltages and they are all within specs. I don't have a HV probe so I haven't checked the high voltage. Anyone have any ideas?

 

[elebish]

Almost all scopes above 5 megahertz BW, will dim down when checking progressively higher frequencies. This is due to the higher horizontal sweep speeds and the persistence of the screen phosphor. The better scopes will have a circuit that will brighten the crt when advancing the sweep speeds. The 2215 must have a problem in the enhancement circuit. If the crt is weak, the traces would be out of focus with the brightness turned up higher than needed. If the crt is really weak, the trace will bloom under the same conditions.

 

[Heliman]

The trace doesn't bloom and it focuses just fine. The scope does have a Auto Intensity. I thought it might be the problem so I checked all the components related to that circuit and cant find any problems. I do have a old Heath scope which is a 40Mhz scope. I can run it up as high as my frequency generator will go which is 35Mhz and the trace is bright and easily visible but it has a manual intensity knob.

 

[elebish]

This may be normal for this scope. I would check with the Tektronix people.