Re: 465 repair, CRT issues

donald collie
 

Hi Lorn,
I have a 475, which is similar. I`ve noticed that it needs the covers on,
otherwise it will pick up hum and either produce a triggerable trace, about
2 minor divisions high, or a thick trace at higher sweep speeds. It will do
this even at insensitive attenuator settings, meaning that the pickup
probably is in the Y amp itself. I suggest you try it with cover on.
Cheers!.............................................................................................................................................................................................................Don
Collie

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On Mon, Apr 30, 2018 at 2:47 PM, blackholenulled <lorn@...> wrote:

What's interesting is my 465B developed the same problem when I took the
cover off (see "465B won't trigger" thread).
I noticed on slow time scales where more pulses are displayed that I could
clearly see a sine wave superimposed on the top and bottom edges of the
waveform. On the faster time scales (zoomed in if you will) the sine wave
isn't visible but the trace looks doubled. Probably because one sweep is at
one point in the sine wave and subsequent sweeps are at a different point.

I'm still working on mine so I haven't had a chance to put the cover back
on to see if it goes away. I've just suspected the scope is sensitive
enough to pick up stray AC, for instance from the fluorescent lights or
it's own power cord.

So try zooming out the waveform quite a ways and see if there is AC
superimposed. If you find a cause other than what I've mentioned I'd be
interested in knowing.

Thanks!

Lorn
KK4KRI
On Sun, Apr 29, 2018 at 04:26 pm, Offelis wrote:


I recently acquired a 465 in rather good condition, and have been
cleaning it
up over the weekend. Power supply rails have been checked to be within
spec,
including the -2450V one. CRT bias adjusted according to service manual
as
well.

Having just finished converting the volts/div indicator lights to LEDs, I
unfortunately stumbled onto a more serious seeming trace issue. At a low
intensity setting, the trace is as one would expect, albeit not
particularly
sharp, but still quite usable. However, at the intensities required at
faster
sweeps (50u/div and above), the trace takes a very peculiar appearance of
doubling itself! This can be controlled at will with the intensity knob,
and
the two "traces" appear when the focus is at sharpest. Here are some
pictures
of the issue: http://oi68.tinypic.com/6jjcdz.jpg

The issue was not present just a day or two ago, so is it possible that
the
CRT has given up the ghost over the ~10 hours or so of power-on time
during
testing and adjustments? Hoping someone can shed light on this oddity.



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