Tektronix 2205 Oscilloscope with flashing trace..

[Tubejunke]

I bought this Tektronix 20Mhz scope to increase my knowledge and capabilities in radio and TV troubleshooting. All of the functions seem to work, but the trace constantly flashes. I have seen videos on YouTube of other scopes and some do the same thing and others have a nice, non strobing waveform.

I'm just wondering if anyone knows about this. Is it normal for some models or is it a defect. It's not actually strobing, but more of a rather large variation in intensity on a steady and constant frequency. It is less disturbing of course if I turn the intensity down low. I am thinking that when there is no signal applied that the flat line is steady.

Any advice here would be greatly appreciated