When a Tek 7104 mainframe has no modules plugged in, should it be possible to see a visible trace?
not a trace;no sweep ramp which has to come from a Horiz plug-in,thus no beam deflection.(or positioning) You can get a spot,though.But you need to turn up the intensity or CRT bias for that,as you get no unblanking pulse which also has to come from a Horiz PI. 7K mainframes were NOT intended to be operated without any plug-ins installed.
In Jim Yanik typed: Thanks. I didn't want to run it like that for any length of time -- just check if the mainframe and CRT were good. So, I take it, there is no point in risking damage to the CRT since it wouldn't be a thorough test anyway.
If you want to know if the CRT is good,then you *should* use a pair of plug-ins;you want to adjust the intensity controls,check for double peaking,move the trace around to check for distortions or dead or hot spots,which indicate electron gun damage,loose particles inside the envelope.I've seen CRTs where you could not get a straight trace,or had particles stuck to the phosphor causing halos,dead spots,traces burned into the phosphor,etc.Even bad geometry.