Tektronix 465B Unstable Trigger

[cjs2pc]

Hi guys,

My Tek 465B scope has some issues triggering when the source is set to Norm under certain circumstances.

The trigger light comes on, but the waveform display is not stable and walks across the screen. Sometimes one channel is stable, but the other is not. Often neither is stable.

I want to use the Norm setting so I can get a view of two channels at once.

Example Setup: 1 KHz square wave calibration signal, 2 channels active and trigger level adjusted so the trigger light is lit for triggered.

• It will stablize fine on some time divisions and not others
• Adjusting the trigger holdoff slightly from centered will sometimes cause the display to stabilize
• Switching from AC trigger coupling to LF Reject will often cause it to stabilize
• Setting source from Norm to Channel 1 or 2 works just fine for that channel
• Leaving it on Norm and turning off channel 2 will cause channel 1 to stabilize
• Sometimes the trigger light pulses very rapidly

I don't have experience with analog scopes and this one is new to me. Is this a normal thing, or do I maybe have some issues with my triggering board?

I absolutely love this scope and want to fix it if I can.

Thanks,

[oldway]

It looks like a bad contact problem.
The semiconductors are mounted on sockets. Stir the transistors and tunnel diodes from trigger and base time circuits in their socket (with power switched off)
Clean the contacts.
Also check the power supplies, especially the ripple.
If it does not solve the problem, you will have to have another oscilloscope to probe this one.

[cjs2pc]

Thank you, I shall give that a try. I do have another oscilloscope if needed.

[KWKolb]

It may be operating correctly.  According to the Tek 468 operator's manual, page 18, "Source Switch:"  "The waveform displayed on the CRT is the source of a composite trigger signal.  Stable triggering of non-time related signals usually can be obtained by setting VERT MODE to ALT, SOURCE to NORM, COUPLING to LF REJ (high frequency signals only) and adjusting thru Trigger LEVEL control for a stable display.  Time relationship between the Channel 1 signal and Channel 2 signal is not indicated on the display."

A case of only having one trigger level for two sources. LF REJ or AC Coupling removes any DC bias between the Channel 1 and Channel 2 signals, allowing a single trigger level to be used for non-overlapping signals.  "A trap for the younger players, there."

I believe the Tek 465B is similar, although I could not find a similar reference in the Tek 465B manual.

VR,
Kevin