Fixing squint traces on a TelequipmenT D61a Oscilloscope

[Garry G]

Hello, I've just took delivery of an old TelequipmenT D61a Oscilloscope and the traces are running at an angle. I looked through the instructions but can't see anything that relates to this. I saw a picture of the machine turned on before delivery and the trace lines were straight.

Could this have been caused by the deflection coil being moved during shipping. Or is there likely a simpler answer?
If it is the coil is this easily fixed? Sorry if these are silly questions, but I'm not used to old CRT Oscilloscopes.

Although I would use this as an oscilloscope in general if I can get the display fixed, I really wanted this for testing a Vector drawing program I'm writing on an Arduino, and making sure my simple circuit and XY cable is working properly.
So worst case my picture is going to be squint!

Any help would be much appreciated.


Thank you.

[cvanc]

Welcome to the forum.

Yes what you describe might be caused by something shifting in transport but there is another possibility.  I have a couple of older scopes that I dearly love but have poor magnetic sheilding around the CRT.  The real-world effect of this is I have to readjust for a level trace at every location I use them in.  This adjustment is called trace rotation.

An easy way to tell if this is your problem is to physically move the scope around to see if trace rotation changes, or try it in some new location, etc.  If it does change when you do this, it's a sheilding problem and probably normal for this particular model of scope.

[bob91343]

I don't think there are deflection coils; it's electrostatic.  Perhaps somehow the crt got rotated in shipping and needs to be turned back.

[james_s]

Yes it is definitely electrostatic, there is no deflection coil. It's possible that it has a trace rotation coil however it looks like it uses a round CRT and in many scopes like that you adjust the trace rotation by loosening a clamp and rotating the whole CRT.

[Garry G]

Thanks  for all the help. I tried it in a few different rooms and it still looks the same, so seems like the tube may have shifted.
That sounds like a fairly straightforward fix though.

[perdrix]

I think there's a small hole in the front panel going to a trim-pot for trace rotation.  There is on a D75.

David