I read AC no problem on my scope but for some reason when it comes down to DC I have to push the TV Line PP button on the trigger section. Why is that? I have a Tektronix 2221A
Did you read the manual? For DC, there is no signal upon which to trigger, so you use the PP Auto setting to initiate a baseline trace in the absence of an adequate trigger signal. See the link below. Refer to pages 2-17 and 3-25.
I looked into the manual but I guess I didn't see it. My friend has a different Tektronix an older model as well and as far as I can remember all he as to do is flip to DC on the channel input he doesn't have to use the trigger
On most scopes if the trigger mode is set to NORM or AC or DC it will not trigger unless there is an AC waveform. If the trigger mode is set to AUTO then it will provide a baseline trigger even with a DC or no input.
Your friend likely has his scope trigger set on the AUTO position if he doesn't have to change it when going from an AC to a DC input.