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Hi i have a 453 with triggering issues,This 453 seems to trigger fine with an input on cha (ie the call signal),chb wont trigger unless i have a T piece and feed the call input to both bnc's ch a+b,it wont trigger on ch b unless a has an input also from the call bnc,is that normal,thats with trigg set to internal,also if set to line the waveform moves slowly across the screen,but is ok set to int,any ideas?,i have changed ch a tunnel diodes ans a few resistors and caps as it was suffering from old age and wouldnt trigger on ch a,also cleaned the switches,A is now working b doesent unless cha is fed a signal too.

can no one shed any light on this?,it seems odd to need a signal on chan A to be able to trigger on chan B input,or am i missing something?

Looking at the pictures of the front panel controls on TekWiki, and reading the manual, it sounds like the 453 only supports triggering on Ch 2 in the NORM trigger mode selected by the TRIGGER control between the two vertical input clusters. Reading further into the manual (and looking at the front panel images for some versions of the 453) seems to indicate that internal trigger is only available on Ch 1. There is some talk about the NORM mode triggering from the displayed channel, but I don't see where or how that is implemented, and there is specific language in the circuit description section that indicates that Ch 2 does NOT have trigger pickoff.

You may need to calibrate your understanding and expectations of this scope.

-- Jeff Dutky

so in a nutshell,is my scope triggering iffy?

in a nutshell, your scope is working correctly. Your expectations, and possibly your understanding of the controls is iffy.

Please don't take this as an insult. The 453 is a relatively old scope, and its features do not align with scopes even a few years newer. The Tek documentation, while excellent in many respects, can also be very terse. I do not think that the 453 service manual does a very good job of explaining the trigger controls and functions, especially when read by someone who is just used to being able to trigger from any input channel (meaning anyone who has used a scope since around 1970). Even the more detailed Circuit Description section is not very clear about this.

On page 3-3 of the service manual (from TekWiki here ) the description of the Ch 2 Vertical Preamp reads:

The circuit differences between Ch 1 and 2 Vertical Pre-
amps are: (1) No trigger pickoff circuit in Channel 2; (2)
INVERT switch in Channel 2. R152 and C159 provide about
the same loading for the Channel 2 Feedback Amplifier,
Q134B and Q154, as the Channel 1 Trigger Pickoff stage
provides for the Channel 1 Feedback Amplifier. This pro-
vides equal response from both channels.

Further on, on page 3-6, there is a diagram (Fig. 3-5) that shows the routing of the Ch 1 and 2 signals with regard to the trigger generator input, which clearly shows that you can either have (1) Channel 1 go directly into the trigger generator via the Ch 1 Trigger Pickoff, or (2) you can have both channels go to the trigger generator after being combined into the multiplexed vertical signal. The description of the TRIGGER PREAMP reads thus:

The Trigger Preamp amplifies the internal trigger signal
to the level necessary to drive the Trigger Generator. In-
put to the Trigger Preamp circuit is selected from either the
Channel 1 Vertical Preamp or the Output Amplifier by the
TRIGGER switch.

When the TRIGGER switch is in the CH 1 ONLLY posi-
tion, the trigger signal is obtained from the emitter of Q63.
The neons B400 and B401 indicate that the TRIGGER switch
is in the CH 1 ONLLY position. In this position of the TRIG-
GER switch, the CH 1 OUT connector, J402, is disconnected
from the circuit.

The trigger signal in the NORM position is obtained from
the collector of Q284. Since the signal is taken off fol-
lowing the dual-trace switching, this signal will be a sample
of the composite vertical signal which is displayed on the
crt. When the TRIGGER switch is in the NORM position,
the CH 1 neons are disconnected. Also, the Channel 1
vertical signal is applied to the CH 1 OUT connector. This
output connector can be used to monitor the signal ap-
plied to Channel 1 INPUT or, when used in conjunction
with Channel 2, can be used to provide 1 millivolt/division
minimum deflection factor.

I've had mixed results with trigger modes (on much later model scopes) that are supposed to trigger off whatever inputs are enabled in the current vertical mode. On some scopes it's apparently bulletproof, and on others it's a crap shoot. I do not discount the possibility that I'm not operating the scopes correctly: scopes are complex beasts, easily misconfigured, and unforgiving of a novice operator (like myself). It is, in my experience, staggeringly easy to get the scope in a configuration where it appears to be dead, when in fact you have simply set one or two controls in a fortuitously wrong way.

Maybe there IS something wrong with your scope (it's old, things get tired), but I suspect that it is working as designed. Specifically, if you had the TRIGGER control set to NORM where it would be taking trigger input from both channels, the only way for it NOT to respond to Ch 2 would be for the Ch 2 signal to be completely absent from the display. More likely, however, is that you have the TRIGGER control set to CH 1 ONLY, and the scope is doing what it says on the tin.

-- Jeff Dutky

i notice if i set the trigger input to line,i cant make the cal trace stable on either channel,it walks either one way or the other across the screen,its fine and stable tho set to int,any ideas,is this filter caps going south?

Why are you surprised by that - setting trigger to line triggers on the mains frequency. Why do you expect the calibration signal to be locked to that?

David

Well as far as i know its all derived from the 50hz mains as far as i know,its just i am certain it used to trigger ok from line a while ago.

It is STILL triggering ok from the line, but the signal you are trying to view is not in phase with the 50 Hz line cycle.

Your scope is triggering fine, you just seem confused about how the scope works.

Maybe the filter caps ARE going south (it's an old scope, caps don't last forever), but that has nothing to do with the trigger "problems" you think you are seeing.

-- Jeff Dutky

If I understand what you're saying, the calibrator is not derived from the line frequency. It's a separate oscillator that's typically somewhere close to 1kHz.

Thanks,
Barry - N4BUQ

so why iser. triggering from the trigger line select ok when from line not?,it was fine if i remember.

Why would you expect the cal trace to be synchronous with the line?

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

It could be that the calibrator happened to drift to some multiple (e.g., 20) of line frequency at that moment, fooling you into thinking that there was a causal relationship. There isn't.

Again, think: Why /should /a calibrator provide a 1kHz-ish signal that is synced to the mains? What would be the point of a scope designer expending the effort and cost to make it so?

Before jumping to the conclusion that the scope is doing something wrong, it's better first to understand what the "right" scope behavior is.

A Tek scope is not overly complicated, but it's not exactly simple, either. For a beginner, reading the manual is not a bad idea at all, especially if every surprise triggers (pun intended) a worry that you have to fix something.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

Hi, here my 2 cents:

"Line trigger" is derived inside the scope from your grid frequency, mostly useful to look at things like grid ripple on a linear power supply, or a signal inside an grid tied inverter, or a dimmer circuit, etc

"Internal trigger" is used to look at signals inside a device under test, like a sync pulse of a old school television signal.
Sweep trigger is derived from Ch1 or Ch2.

"External trigger" is similar to "Internal trigger", but now you use the External trigger input to start the sweep, and one or both inputs to look at signals inside the device under test.
This can be useful when the signal you want to look at is very small so triggering can be difficult, and when a clear flank in sync with the signal you want to look at is available, so you can use that to trigger the scope.

Hope this helps,

Leo