Oscilloscope Problem

[flyingfrancisco]

Hello everyone.
I have a Kenmore dual trace 20 Meg oscilloscope that I am having a problem with. The traces are " Quivering" which was not the case before. Does anyone have any ideas of what in the circuit could be causing this. Also I am  not a tech, just a hobbyist so please keep your answers simple
Francisco

[alm]

My first guess would be dried out caps, resulting in increased power supply rippling coupling into the vertical or trigger circuit. Try measuring power supply voltages and ripple. Second guess would be bad switch contacts, try cycling the switches a few times. Both are fairly common in old scopes.

[flyingfrancisco]

Thx for your quick reply!

[benemorius]

What frequency is the signal you're looking at? (Or is it every signal you've tried?) Likely causes are noise and/or a higher frequency signal mixed with the one you're trying to see. Some scopes have options to filter these from the triggering circuit.

[w2aew]

Also, what are you using for a probe? And, what is the nature of the circuit node that you are looking at (high impedance)?  Poorly shielded probes and high impedance circuit nodes are susceptible to stray pickup of 50/60 cycle noise from the mains - which can make the traces wiggle.

[Fraser]

Place the oscilloscope in X-Y mode with no inputs. You should see a nice stable compact dot on the screen. Check focus and brightness. If the dot is oblong or quivering, you have noise in your input stages most likely caused by PSU ripple. As has been stated, failed smoothing capacitors can cause PSU rail ripple.

Aurora

[siliconmix]

kenmore.never heard of that make.i'd agree with whats been said about the caps.is there a 60 hz ripple on the trace also?

[jimmc]

My first thought would be to check whether you have recently placed any mains powered equipment near the 'scope.

The stray magnetic field from some mains transformers is quite large and can cause the trace to quiver by directly deflecting the electron beam in the CRT.

Jim