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
