Need help with oscilloscope

[error0]

Hello

I have some problems with my Telequipment D67A oscilloscope and I was hopeing someone would be kind to help me sort it out.

The trace of for example a sine wave distorts around the x-axis where y = 0. If I offset the trace up or down it resembles the input signal more the further away from 0 it goes.

Please see image

An externally hosted image should be here but it was not working when we last tested it.

 

[cuibono]

Maybe you could try the yahoo group for tek oscilloscopes - there are some really knowledgeable people there. If you get a yahoo account, you can post...

http://tech.groups.yahoo.com/group/TekScopes/

 

[unclejed613]

the oscope has a deflection driver similar to a class-B amplifier. looks like this one has a problem with crossover distortion. could be a bias problem in the deflection amp, causing a nonlinear gain change at the crossover point. the other possibility is that the distortion is from the sine wave generator (check it on another known-good scope). you will need a schematic and a calibration manual for the scope. the calibration manual will have the location of every adjustment in the scope. right now you want to concentrate on the V amp bias. the scope probably could use a good cal, but to do it properly you need test equipment that is very rare on the second-hand market, such as time-base standards and stairstep voltage standards.