Hi!
Do you have another oscilloscope available?
You'll need one to diagnose this fault as the triggering circuitry may not be set-up or working correctly!
Download the SC504 Manual from TekWiki W140, BAMA Archive or Kevin Chant, etc., (it is a good PDF and all complete!) and first of all, go thro' the basic operating procedure as given in Pages 12-18 just in case it's some perculiarity of front-panel switch settings etc., if you are completely happy the trace doesn't respond correctly to the basic operating procedures in pages 12-18 of this manual, you will need another oscilloscope and DMM to investigate the triggering/free-run circuits and the horizontal amplifier.
As with all faulty Tek equipment, the internal power supply voltages MUST all be correct, both for voltage and ripple BEFORE any detailed fault-finding can be carried out on the remainder of the circuits! (Diagrams 8, 9 and 10)
If you have, or can get access to another oscilloscope, begin by referring to the wave-forms given on Page 79 of make sure all of these are present and correct.
If you find anything that doesn't look right, take a picture of the faulty waveform (a phone camera will do) and post it - one of us will be on hand to assist!
The relavant circuit-diagrams you need to study are:-
a) Diagram 4, TRIGGERING, on page 91;
b) Diagram 5, SWEEP GATING, on page 94;
c) Diagram 6, SWEEP GENERATOR, on page 97,
d) Diagram 7, HORIZONTAL AMPLIFIER & OUTPUT BOARD, on page 99.
If you feel this is too difficult or you don't have enough equipment, and you're not too far from Birmingham/Midlands (your name shows as a UK poster) please PM me and I'll get back in touch by PM with a view to assisting personally!)
Chris Williams