Tektronix 2235 Oscilloscope troubleshooting

[Parry]

Hi All,
I am a newcomer to this electronics hobby late in life. I have a smattering of knowledge more than enough to keep me out of danger. I recently bought a Tektronice 2235 oscilloscope which was working when I picked it up and looks to be in good condition. On the second time I fired it  up I could not get a trace. Pressing the find trace button showed a spot near centre screen. Calibrating a probe I could get a trace approximating a square wave that occupies the middle third of the screen when pressing the find trace button. This disappears when released. so far no amount of twiddling of knobs an d buttons cannot get a display without using the find trace button. Does anyone have any ideas?
Your help would be greatly appreciated .
Many thanks, Parry

[andy3055]

I would first download the service manual and check the Low voltage supplies first. You can get the manuals from here: https://w140.com/tekwiki/wiki/2235

[Parry]

Thanks Andy I will try that.
Parry

[bdunham7]

so far no amount of twiddling of knobs an d buttons cannot get a display without using the find trace button. Does anyone have any ideas?

Post a photo of the complete front of the scope as you are trying to operate it and perhaps we can tell you which knobs and buttons you need to get a trace on screen.

[Parry]

Hi bdunham7,
Photos attached.


Thanks

[bdunham7]

Hmmm.

Make sure both intensity knobs are all the way up and the horizontal position knob is close to centered.  Change the Horizontal Mode to A instead of ALT.   Hook up a 10X probe to CH1 and connect it to the probe calibrator output, then change the A TRIGGER to Normal and see if you can get the trigger light to come on by adjusting the trigger level all the way from one end to the other.

If none of that works, disconnect the probe, set the timebase knob to XY and see if you can get a dot on the screen by adjusting the CH1 and CH2 position knobs.

[Parry]

Many thanks. Doing as you say I can get the square wave on the screen and the trigger light to com on. Removing the probe the trace disappears. I can get a horizontal trace with the probe removed from the calibration but still attached to the scope by adjusting the level. the level adjustment is very sensitive. removing the probe the trace disappears but can be returned momentarily by adjusting the level but cannot remain when left alone.

[bdunham7]

Many thanks. Doing as you say I can get the square wave on the screen and the trigger light to com on. Removing the probe the trace disappears. I can get a horizontal trace with the probe removed from the calibration but still attached to the scope by adjusting the level. the level adjustment is very sensitive. removing the probe the trace disappears but can be returned momentarily by adjusting the level but cannot remain when left alone.

OK, then with the probe installed but not connected to the calibrator output, press the AUTO P-P button without changing anything else and see if you get a continuous horizontal trace.  If not, connect the probe to the calibrator output and adjust the trigger level again to see if you can get the square wave to appear in the AUTO P-P mode.

[Parry]

Hi bdunham7,
We seem to have success. Attached photo shows a trace from an IPad based tone generator. The level knob now is rock solid. I am relieved that there seems to be no hardware issue that I can see. I will now try other functions to see if that is indeed the case. I am indebted for your advice. If there is anything else I should be aware of please let me know. When I find other gaps in my knowledge i will post again.
Cheers,
Parry