Re: 475 hor.jitter


dhuster@...
 

Rich, the 465, 465B, 475, 475A, 464, 466 and 468 had identical fan
modules. And by the way, this has nothing to do with bearing noise,
but if you have a fan that has a dead spot and won't always start up
and you don't know whether to blame the motor or the driver chip,
just put the motor on the dead spot and then pull the driver chip and
reinstall it "backwards". It has a symmetrical pinout, and if one of
the transistors in the driver chip is bad, you'll have moved it to a
different spot in the switching sequence, the motor will no longer be
on a dead spot with the reversed chip and will probably start up when
power is applied. If the dead spot is still in the same place, then
you can blame the motor.

And Rich, the 475 has had several reliability mods over it's life,
and if you have a lower serial number, it may need some of them.
The -8v P/S should have a new rectifier that's much larger than the
others (i.e., it's NOT a 152-0488-00) and will be laying down rather
than standing up in order to clear the case.

There's also a bluish 1% resistor (with the scope upside-down as you
look on the main board with the front panel facing you, it's along
the left edge maybe 2 or 3 inches from the front) that overheats,
turns brownish and changes value, goofing up the timebases. If
there's a black resistor in that spot, the mod has already been
made. Otherwise, it needs replaced with a higher-power resistor.

And the one mod that may concern you most is down near the hole where
the horizontal deflection plate leads go down to the jug. An
unmodified scope has a silver-colored, axial-lead, tantalum, 1000µF
capacitor just to the front of the hole. If it's there, get rid of
it, for it's underrated in voltage and will cause a jittering
problem. A modified scope usually has a physically-larger, black
aluminum electrolytic with a higher voltage rating installed in it's
place.

Dean

Join TekScopes@groups.io to automatically receive all group messages.