How to test a Tek 475 oscilloscope?????
Dave Platt
Igor9954 <ignora...@NOSPAM.9954.invalid> wrote:
>Sorry for a stupid question. I bought a tektronix 475 fairly cheaply. It
>also had a DM44 on top, which I interpret as a digital multimeter.
Yup. It's not just that, though - you can do some neat time-and-
frequency-based measurements with it, too.
>This thing does power up. When I press "BEAM FINDER", a bright dot appears.
>When I switch between 100 and 200 MHZ, a line blips on the screen briefly.
>
>I would like to make this thing display a nice horizontal line or maybe
>even the 60hz sinewave. How would one do it? Suggestions will be greatly
>appreciated.
Set the horizontal sweep to one of the slower settings and the trigger
to "Channel A", set the input selector to "A", and set the sweep mode
to "Auto". This should cause a horizontal line to appear... the
horizontal sweep will trigger automatically if there's no initiating
trigger event within a couple of scan-completion times. This will let
you see the trace, at least. Adjust the brightness to a moderate
level, and then adjust the focus.
Connect a probe to the "A" input, and clip its end to the calibrator
(the U-shaped wire widget). Set the "A" input sensitivity to 1
volt/division (if you're using a 1x probe) or 100 mv/division (if
you're using a 10x probe). You should then see a trace which shows a
square wave. It may or may not have a clean appearance. Rotate the
trigger-voltage control in either direction, until the calibrator
trace "locks in". If you set the sweep mode to "Norm", it'll only
trigger a sweep when the trigger voltage is reached - you'll either
see a fairly clean square-wave trace, or no sweep at all. Try several
different sweep speeds.
Then, try removing the probe tip from the calibrator, turning the
A-channel sensitivity 'way up, and touching the tip of the probe with
your finger. You should see a noisy 60-cycle waveform appear, as your
body acts as an antenna and picks up the induced powerline noise.
You may see even more than just a sinewave appear. When I was working
to repair my Tek 465 a couple of weeks ago, I noticed that merely
holding my finger in front of the A-channel BND connector (with no
probe applied) would cause a 60 Hz waveform to appear... and there was
a really big, sharp noise-spike right in the middle of each sine. I
was afraid for a moment that this indicated that I had a noise problem
inside the 'scope. Then, on a hunch, I reached over and switched off
the nearby pole lamp (which has a triac-based dimmer circuit). Still
got the 60 Hz sinewave, but the spike was gone - it was RF switching
noise from the dimmer.
--
Dave Platt dpl...@radagast.org
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Jim Yanik
<tqnluip...@corp.supernews.com>:
Some of the new compact fluorescent lamps designed to replace incandescent
bulbs also have a lot of radiated noise,from the electronic ballast.
--
Jim Yanik,NRA member
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