Tek 2225 Scope Ripple on Display - Advice Please

[Nick Thorpe]

I recently bought a Tektronix 2225 sold as ‘spares or repairs’ and for a very low price. It was initially displaying the two channels quite happily and would auto trigger on channel one but wouldn’t lock on channel 2 when using the test output. The displayed square wave was fine and in calibration.

The next day this ripple or noise appeared on channel one. I tried different probes, mains supply etc. but it is still there. It is the same without probes attached.

I have read many threads on t’Internet, downloaded and started reading the service manual and other Tek repair manuals. I have also watched Dave’s YouTube videos.

Could anybody point me in the right direction for how to repair or diagnose this fault?

Many thanks,

Nick

[tggzzz]

Insufficient information! (But the photo is a better start than many people manage )

What's the frequency, amplitude, scope control settings, probe and probe connections?

What makes it better and worse? Scope controls? Probe position? Phase of the moon?

Be careful when poking around in a scope. Make sure you really do know where the "entertaining voltages" are!

[djsb]

What is the amplitude and frequency of the ripple? Does the ripple stay the same over time? Does it change when you operate the switches? What happens when you ground the input? I'm sure you can think of a few other questions?

Can't really suggest a solution though, but this place may also be helpful

https://groups.io/g/TekScopes

I also have one of these scopes. I might dig it out of a cupboard and see if it still works.

[George Edmonds]

Hi Nick

I have repaired a number of this series of scopes, they all have a common weakness in that the power supply electrolytics fail.  They are primarily but not only 840uf at 12VDC (use 1000uf) and 270uf at 40VDC all 105 Celsius working.  These must be good quality such as Rubicon. or Panasonic

Make certain that you are using the correct manual for your scopes serial number.

Be very careful if doing live testing there are nasty and possibly lethal voltages present in the power supply area,  There is a screw in the side panel towards the rear, this must be finally replaced as it is part of the heat sink for the power supply.

G Edmonds.

[wn1fju]

For what it's worth, I had a Tektronix 2215A scope that exhibited noisy oscillations (about 25 kHz) on one channel at low V/div settings (<=5 mV/div).  I suspected switching power supply noise and while I had the scope opened up, I noticed that when I twisted the chassis a little, the noise on the trace went away.  I tightened up all the hardware, including a little ground clip that touched the metal cover surrounding the CRT.  The noise on the channel disappeared never to be seen again!