"Dick" wrote
My Tek 465 scope has developed a minor but annoying fault in its
triggering circuitry

It sounds (reads) like a bad connection.

By Ole Occam's razor, and a description of the problem - 'it works
till I touch the knob' - my first guess is a dirty and/or worn
synch selection switch or trigger level pot. The pot wouldn't
happen to have one section for Ch. A and one for B and get
bypassed in Auto, would it?

If it were mine, I would first try a spritz of contact cleaner into
the switch via the front panel slot (IIR465C). All contact
cleaners are the same - mineral oil and alcohol - so the cheapest
Radio Shack stuff works as well as anything. WD40 also works well.

Getting to the switch or pot by disassembly I would save for last.
There is an old adage "Fix anything long enough and you will _really_
break it." And I wish I would remember that adage in time.

Other likely causes are bad connector, crimp or solder joint. After
that electrolytic caps.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

OP:

"Dick" wrote in message
...
My Tek 465 scope has developed a minor but annoying fault in its
triggering circuitry but before diving into the guts of an old &
faithful friend I would appreciate it if anyone who has experienced
similar symptoms to those below could give me their thoughts on possible
causes & (more importantly) how they fixed their particular version of
the problem.

1) My scope just won't trigger in the A Normal mode although a stable
trace obtained in A Auto will remain displayed (and stable) in A Normal
until I touch either A Trigger slope or polarity controls.

2) I can stabilise a trace using the A Auto mode but only by adjusting
the A Trigger Hold-off control rather than the A Trigger slope/polarity
I would normally expect.

3) Everything appears to be triggering correctly when I use the B
Trigger.

4) All other scope functions appear to be OK.

I've checked these symptoms and they seem to be present what
ever type of signal I'm inputting - sine/square, 1kHz - 1MHz, Ch1 or
Ch2.

I've got a set of battered circuit diagrams & layout drawings so
should at least be able to follow up any ideas you experts might be able
to pass my way.

In the mean time many thanks for at least reading this posting
and Merry Xmas & Happy New Year to everyone fra' Auld Reekie
--
Dick
GM0MNL