Re: Tek 454 Ch1 Vertical Drift

Terry Brown <terry.brown6@...>

Stan, I removed and reseated all the Nuvistors I could find and also checked
transistors in the sockets to see if loose. That seems to have solved the
drifting issue. I'll let it cool down completely and retry later.
Are the 454's very sensitive to movement...i.e., do the
transistors/Nuvistors and other parts move around with just normal carrying and
storing of the scopes?
I also noticed that the leading edges of the calibrator square waves have a
slight upward/downward curve to them (even using a straight patch cord in place
of probes). Is that normal or does it indicate some need for recalibration?
Thank you, again, for all your help and sharing of knowledge.

Stan or Patricia Griffiths wrote:

terry.brown6@... wrote:

Stan (or others), you have helped me with this scope just recently. I
picked up an original users manual which is great! But, my scope has
just started giving me trouble with Ch1. When I turn the unit on, and
even after an ample warmup period, the Ch1 trace doesn't show up. I
locate it with Beamfinder but can't get it stabilized on the screen.
When I can get it to position, it continues to drift vertically, both
up and down, and will not completely stabilize (even after 30 minutes
or more). That is with leaving the Volts/Div control in the same
position. Any ideas?
Also, I discovered the Ch2 Cal control has absolutely no effect. I
can't find a detent position either. I thought it might be a loose
knob but that wasn't the problem. What do you think? Thanks, much.

Hi Terry,

Here is an educated guess. I suspect you have two problems. The drift is
probably due to a bad nuvistor in the Ch 1. You might just try reseating it
in the socket.

The lack of detent in the Ch 2 Variable Volts/Division control could be due
to a broken shaft coupling. I can't remember if there are shaft couplings
here or not. This may be a real tough one to repair because it will be
buried under the CRT shield. I might have a part for this if you can
determine what you need and can get to it. If this turns out to be one of
those white plastic pots with a crack in the part with the set screw in it,
one way to fix it is to back the set screw out and epoxy the plastic. You
have to let it sit for a couple of days to make sure the epoxy is real hard,
then retighten the set screw.


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