Most likely a bad capacitor. It's late here and I don't have time to dig
into the manual tonight. You might take a look at the power supply schematic and
follow how the -8 volt supply is derived.
?
The -8 must be good or the scope will not work.
?
Just for the exercise, talk?your ohm meter and check that the -8 volt
test point is not shorted to ground. If so, the next most likely thing is a
shorted tantalum capacitor. Take a look at the power distribution schematic the
see where the -8 volts goes.
?
?
Have fun,
Tom
?
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----- Original Message -----
Sent: Tuesday, January 15, 2013 1:32
AM
Subject: [TekScopes] 465B Oscilloscope No
-8V
?
Hello, I am trying to fix my Tektronix 465B Oscilloscope. I have the
service manual and have been using it to try and figure out what's wrong. When
turned on, there is nothing on the screen, even when pressing and holding beam
finder, and the power light doesn't come on. The only control that seems to
work is scale illumination, which makes the screen glow orange when turned
up.
I checked the voltages at the test points on the main board A4 as
described on page 4-24, and found all of them to be within spec: +55, +15, +5,
and +110, EXCEPT for the -8, which measures 0.2mV. The power supply wiring
diagram at the back of the manual shows two blue wires from the transformer,
going through a fuse F4501 (desoldered and removed from board, it's good),
then through a rectifier bridge CR4411, which is also good.
So where
do I go from here? What voltage should I be seeing at the two blue wires,
because I'm starting to suspect that part of the transformer? Thank
you
