I'm finding that my elderly Tek 2235 CRO (a very nice 100MHz Dual-trace) can't focus the spot any smaller than about a millimetre in diameter, & that is at the the extreme anti-clockwise setting of the front panel focus control. Turning the control clockwise can defocus the spot to nearly size of the whole screen. I assume this is due to component aging, rather than an actual fault.
Does anyone know if there's an internal focus control or setting (an HV adjustment?) I can to adjust to re-centre the main focus control?