Magnavox horizontal hold

If there are no "user" adjustments (knob or access holes) on the front, sides or back), you probably will have to take the back off of the set. There is probably a trim pot somewhere on a board.

Note: Be very careful messing around due to shock hazard... even if the set is unplugged.

You may want to take a careful look inside and then post a picture once you think you've located the likely adjustment location before attempting any changes.

Popping the back cover is not risky as long as you know what to be careful of. Just keep clear of the connections at the back of the Tube and the thick wire going to the Flyback Transformer. Look for potentiometers at the base to adjust, keep track of the starting position.

do not know which model or chassis you have but there may be a leaky capacitor in the 130 volt line to the horizontal drive circuit.
I have seen many older Maggies do this and been so long to have repaired one. Look for a capacitor fairly small in size an electrolytic
that may have its top swollen you symptom matches the repair caps cost just a few cents or a dollar for the value you need.
As the other poster state unplug the set from AC the CRT can hold a charge for a loooong time and it is possible to get zapped and believe me
it really hurts. I am 99% sure this is your problem can you supply model and chassis as we have may older Philips/Magnavox schematics still in
our store and repair house.