Mysterious oscilloscope sine wave

Thread Starter

BkBALLER

Joined Jul 24, 2016
8
Good day all. I have a Tektroniks 466 scope, a Wavetek 164 sweep generator, and a Dynatek Navada 628 pulse/function generator. To see if the scope was functioning properly, I put in a 1Khz sine wave from either generator, and the sine wave on the scope is shall I say-distorted? My camera isnt working right now. Sorry. The wave goes like this:If you start at max.negative and going positive, the trace is linier to you get to about a half a gratical from zero,then the trace makes sort of a bend towards the right of the screen then just before zero, it makes a bend back upwards, threw zero and linier to positive max,turns nicely linier towards zero, and about a half gratical before zero, it bends towards the right of the scope,then bends back towards zero, and linier to max, negative, and repaets this way. I read that it could posibale be two signals that were mixed d and the wave is the resolant, or it could be reactance and resisance versus frequency. I do have a copy of:the 44th edition:1967-The radio amatuers handbook, and on page 52,it has a graph of this reactance and resistance versus frequency. On the left of the gragh,starting in the negative and going positive,it has this, shall we say:dog leg I'm seeing on my scope. I doesnt matter which generator the 1Khz signal comes from,the sine wave still has the same:dogleg. I cant believe two differant generators would produce the same result like this. Sorry to be so long winded, I'll get the camera fixed. Thank you very much for your patience.
 

dl324

Joined Mar 30, 2015
16,662
Are you using a scope probe, or is it direct connect?

Can you cobble together a square wave oscillator to see if the scope might have a problem? Using a 555 timer or something?

Your post would be easier to read if you took the time to organize your thoughts into paragraphs.

And you can take your time and post when you have all of the relevant information available...
 

ebeowulf17

Joined Aug 12, 2014
3,307
Good day all. I have a Tektroniks 466 scope, a Wavetek 164 sweep generator, and a Dynatek Navada 628 pulse/function generator. To see if the scope was functioning properly, I put in a 1Khz sine wave from either generator, and the sine wave on the scope is shall I say-distorted? My camera isnt working right now. Sorry. The wave goes like this:If you start at max.negative and going positive, the trace is linier to you get to about a half a gratical from zero,then the trace makes sort of a bend towards the right of the screen then just before zero, it makes a bend back upwards, threw zero and linier to positive max,turns nicely linier towards zero, and about a half gratical before zero, it bends towards the right of the scope,then bends back towards zero, and linier to max, negative, and repaets this way. I read that it could posibale be two signals that were mixed d and the wave is the resolant, or it could be reactance and resisance versus frequency. I do have a copy of:the 44th edition:1967-The radio amatuers handbook, and on page 52,it has a graph of this reactance and resistance versus frequency. On the left of the gragh,starting in the negative and going positive,it has this, shall we say:dog leg I'm seeing on my scope. I doesnt matter which generator the 1Khz signal comes from,the sine wave still has the same:dogleg. I cant believe two differant generators would produce the same result like this. Sorry to be so long winded, I'll get the camera fixed. Thank you very much for your patience.
Have you tried other shapes besides sine? Seeing how the generators and/or scope respond to different waveforms might reveal some clues.
 

Thread Starter

BkBALLER

Joined Jul 24, 2016
8
This is an image of crossover distortion. Does it look like this?
Thank you Alberhall. It looks exactly like your picture. A little more severe, but exactly like your picture. I was using a bnc cable terminated at the scope. As I mentioned, the Wavetek 164 sweep generator and the Dynatek Nevada 628pulse/function generator both produced this same wave. I did seperate my question into paragraghs but it didnt post that. Probably this wont either. But thank you very much for your reply Alberthall.
 

Thread Starter

BkBALLER

Joined Jul 24, 2016
8
Thank you Alberhall. It looks exactly like your picture. A little more severe, but exactly like your picture. I was using a bnc cable terminated at the scope. As I mentioned, the Wavetek 164 sweep generator and the Dynatek Nevada 628pulse/function generator both produced this same wave. I did seperate my question into paragraghs but it didnt post that. Probably this wont either. But thank you very much for your reply Alberthall.
Sorry people. Now I know it might be distortion, the same distortion happens on the triangle setting. The square wave is O. K. and so is the trapizoid setting. Since this happens on both generators I thought the problem was in the scope. I just wanted to narrow down the possible problems so I knew what to research for. Now I can look in the Wavetek service manual for the proper diagnoses. I cant find a service manual for the Dynatek Navada 628. I would appreciate any leeds on where to find one. Thank you again for your help.
 

recklessrog

Joined May 23, 2013
985
You will probably find that the bias to the final Y amplifier transistors is wrong, check the voltages around that part of the circuit and you may find that some of the resistors have gone high in value, or the electrolytic capacitors have become high ESR. don't just measure them, replace them.
Here is a link to the service manual.
https://www.tek.com/manual/466-service-manual

The bias pot is R478. carefully mark its current position, then vary it either way whilst watching the display. If it makes no difference, check all the voltages marked on vertical output amplifier schematic.
P.S. Do make sure that the mains voltage selector is set to the same as your line supply.
 
Last edited:

recklessrog

Joined May 23, 2013
985
I am currently repairing a Phillips Oscilloscope with the same problem. (see the photo's) the signal is pure right up to the output transistors but if you look at the waveform shown on my other scope, you will see it is distorted where it drives the "Y" deflection plates.
The cause is one of the final amplifier transistors has only got an hfe of 5 when it should be more like 25! These transistors have a hard life, and I suspect that some of the multiple emitter connections have failedP1010043.JPG P1010050.JPG
 

Thread Starter

BkBALLER

Joined Jul 24, 2016
8
I am currently repairing a Phillips Oscilloscope with the same problem. (see the photo's) the signal is pure right up to the output transistors but if you look at the waveform shown on my other scope, you will see it is distorted where it drives the "Y" deflection plates.
The cause is one of the final amplifier transistors has only got an hfe of 5 when it should be more like 25! These transistors have a hard life, and I suspect that some of the multiple emitter connections have failedView attachment 137425 View attachment 137426
Thank you Recklessrog. For some reason I cant down load the link you provided. It would have helped if I told you guys my 466 is a low series scope. I do have a pdf of both the low series and the B2000 and above series. The circuit numbers are differant,
 

Thread Starter

BkBALLER

Joined Jul 24, 2016
8
Thank you Recklessrog. For some reason I cant down load the link you provided. It would have helped if I told you guys my 466 is a low series scope. I do have a pdf of both the low series and the B2000 and above series. The circuit numbers are differant,so I was confused about the componants. Some of the componants were removed from the high series, some are just physicaly differant. Now I know where and what to look for I should be able to find the problem. Very, very, very, helpfull info. I apologise if my text isnt in paragh form. I text that way, but it doesnt post that way. They are upgrading the communication lines in my neighborhood, so I have to work off this cheap cell phone. Thank all you people for your help with my problem.
 

recklessrog

Joined May 23, 2013
985
Hi, the link works ok here so may be an issue your end. If you Google "Tektronics 466" you should be able to locate the correct service manual to download. Good luck :)
 

AlbertHall

Joined Jun 4, 2014
12,328
If you adjust the Y-shift so the waveform moves up and down the screen odes the kink stay in the same place on the screen or does it move with the waveform?

If it follows the waveform then the problem is before the shift control, if it stays in the same place on the screen then it is after the shift is added.
 
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