troubles with tektronix scope

[Dirceu]

Hi to all.
I have a TDS684B scope  presenting a "vibrating" waveform. It is in vertical and horizontal directions, as another signal were added to original one. This happens  in  4 channels.
--in self test it pass, no message errors or fails;
--this shake appears to be more intense in higher frequencies input signals;
--without input signal the horizontal trace is fixed;
--this shake is randomly, not a repetitive pattern;
-- the 25 volts power supply is presenting a ripple as noise-it reaches 0,5Vpp sometimes. The other supllies are OK. I did not find yet the reason for this ripple in the 25 volts psu, it seems to be in the first rectifier/multivibrator part. Capacitors are OK.
--there is no schematics.
 Anybody has a tip to help me?
Thank you in advance
Dirceu

[james_s]

The power supply ripple is the first thing I'd check. There is a component service manual out there for one of the 5xx series scopes which should be close enough to help you. Is this one of the era that has leaky SMD capacitors all over? If so then you'll want to replace all of those. Later TDS scopes switched to ceramic chip bypass capacitors.

[Armadillo]

Try temporary disconnect the fan and measure again.