Tek 2246 channel 1

[Tubesrule]

Hi guys, I been putting this of since I'm not scope savy. But is time to get it done. I have two issues with the 2246, first annoying but workable the self calibration. The second is the real problem, channel 1, has no vertical movement at all, I can switch the ac/dc and it shows but no trace. The other three channels are "fine". I already check all voltages and checked fine from 5v-130v. Any input is more than welcome.

Thanks

[David Hess]

The second is the real problem, channel 1, has no vertical movement at all, I can switch the ac/dc and it shows but no trace.

It looks to me like channel 1 is not being displayed at all.  To me that indicates a problem with the digital control of the analog sections.  The 2246 uses TTL SIPOs like the 74164 to control things.  Maybe a bit is stuck.  The service documentation is comprehensive so it should be possible to track down with a multimeter.

[Tubesrule]

Thanks for that, yes you are correct not visible at all only the the beam find shows it(but I can't move it) vertical. Let's do some reading.

[David Hess]

Thanks for that, yes you are correct not visible at all only the the beam find shows it(but I can't move it) vertical. Let's do some reading.

That changes things.  If the beam finder shows it, then the trace is activated and either is not displayed because of a z-axis (intensity) problem, or the trace is shifted out of the viewable area.  The later is likely the problem since the beam finder overrides the z-axis; somewhere in the vertical signal chain, there is an offset pinning the trace off screen.  That also explains the calibration error.

The diagnostic process is the same; the vertical signal path can be traced from the input to the vertical channel switch and likely find the problem.

The input high impedance buffer or the input protection circuitry could have been damaged by an overload to cause this.

[Tubesrule]

Hi, A bit of an update after I read to this awful printout of the service manual, I decided to go back and check voltages and ripple. Dc voltages were fine, ripple on 58V was way up, north of 100 mV but one that I didn't check the first time was the 130v AC which right now is 97V I found the 130Ac going to the Dc restorer circuit, so that's where I'm at. 

[Wallace Gasiewicz]

Did you check the ohms at the various inputs? with the unit off?

[Tubesrule]

No I did not.