Minolta 360px manual mode

I was playing around with a long-ago-acquired Minolta 360px flash last night, and decided, for the first time, to see how well the "manual" mode worked. It has power settings like full, 1/2, 1/4 etc. Well, on "Full" everything worked fine, but when I wet to 1/2 the flash flashed, but not at 1/2 power. Far less. Much like a pre-flash on some flashes.

Did I do something wrong? Miss a setting? Or is my flash dead on manual mode?

If you own a Ferrari it's carbon on the valves. Since it's a variable power flash it's most likely tarnish on the resistor band. Turn it back & forth a bunch of times & it may clear up. If you can get to it(high voltage)in there a spritz of contact cleaner could clear it up.