Hello, I just purchased a Tek 2235 off university surplus with what seems like a similar issue. No trace, however when I push the beam find button, I get some part of a trace that sweeps appropriately with the time base setting. I can also move it up/down and left/right with the X and Y position controls (though with limited movement). When I feed a signal (random sine wave in this case), there is still no trace, however I can see some part of the signal displayed when I push the beam find button. I measured the power supply rails, (or at least the test points on the board) and they all seem to be in spec, so I'm inclined to say that it is not a power supply issue.
Both channels behave exactly the same, so I don't necessarily expect it to be the vertical amplifiers (they'd have to have both failed in the same way). In my case, I've got other scopes that I can use to troubleshoot this one. Some direction on where to start looking, however, would be welcome.