Table of Contents
Advertisement
If
the plate
of V3 can be moved as indicated,
move the
voltmeter
to pin 2 of VhA.
The voltage
should pass
through
zero as R128 is varied,
and at least
20 volts
in the negative
direction.
In the positive
direction,
the grid will
be damped by draming grid
current
a few
tenths
of a volt
above zero.
If the above is not pos-
sible,
check R129, or the voltage
across
C119-C
(about
270~).
Now ineaaurc Vh, pin 1.
This voltage
should also swing
through
100 volts.
If not,
check as for
the previous
stage.
Finally
check pin 7 of VU.
Since this
is the cutput
cathode
follower
it
should
swing both plus and minus
at least
20 volts
upon ma.*ipu1ati0*
of Rl28.
If it
does not,
either
V&B is defective
or FU3h is open.
e.
In some cases,
the instrument
acts as if
It Is extremely
sensitive,
and a signal
much smaller
than the normal
full
scale
signal
drives
the output
full
scale.
The cause in this
case is lack
of negative
feedback
from
the output
to the input.
It may only occur
on some
ranges.
It
is probably
due either
to a defective
switch
contact
or a" open feedback
resistor,
breaking
the fecd-
back loop.
It must be traced
by checking
with
the sche-
matic and locating
the resistors
in question.
I
v-3
Advertisement
Table of Contents
