HP 400D Operating And Servicing Manual page 27

1) Connect a 400 cps sine wave signal to the INPUT
of the vtvm under test.
reading of 0 . 9 0 on the 0 . 1 volt range : Adjust mon­
itor meter to establish a "reference level" on the
upper
end of a convenient range .
2) Change input signal to 4 mc and set amplitude to
"reference level". Adjust capacitor C21 i n vtvm
under test for a reading of 0 . 90.
3) Change input si.gna.l to 1 mc and set amplitude to
"reference level". Capacitor C26
of V4 can be adjusted in value between limits of
15 f.ij.t f and 82 l.q.Lf to control the
you change C26, repeat steps
4) Change input signal to 6. 4 mc and set amplitude
to "reference level".
5) The reading on the vtvm under test should not be
of
more than 5% full scale above 0. 90.
below 0. 90 is acceptable .
undesirable at frequencies above 4 mc.
If
the reading is more than 5% high, add capacitor
if
C40 and resistor RS2
your
circuit of V2 in vtvm.
if
these parts are added.
of
The values R82 and C40
6. 4 mc response below the 5% maximum.
change either
R82 o r C40 in
through 5.
6) Change the input signal to 10 cps and set the am pli­
tude to the "reference level"
vtvm
the under test should be 0.90, :1:5%
To increase the 10 cps indication, remove RSO
present in V2 grid circuit.
if
cuit additional increase is needed after RaO re­
moval. Conversely, to decrease the indication, re­
if
move RBl and add RSO
both resistors can be added.
omitted. A value of 2 . 2 megohms or higher should
RBI
be used for RSO or when adjusting low frequency
response. Check tubes and coupling capacitors
you
find that a resistor value below 2 . 2 megohms
is required.
7) Increase the input signal to about 20 cps and set
the amplitude to the "reference level"
vtvm
reading on the under test should not be more
than :l:2% of full scale from O. 90.
compromise resistor adjustments to satisfy steps
6 and 7.
B) Switch the vtvm unde r test to the O. Ol volt range.
Establish a new 400 cps "reference level" for this
range by setting to 0 . 9 0 on the 0 to 1 scale.
Adjust signal level for a
in the
plate cirCuit
I mc response.
1 through 3 .
Any reading
A high frequency peak is
not already in the cathode
Repeat steps I through 5
can
be adjusted to bring the
If
you
value, repeat steps
of
TIle
step 1. reading on
of full scale.
Add RBl in V3 grid cir­
necessary. Either but not
Both resistors can be
of
step 1. The
If make
necessary,
9) Change the input signal to 4 mc and set the input
amplitude to the "reference level" established in
step 8. The reading on the vtvm under test should
be set to 0. 90 by adjusting capacitor C16.
10) Switch the vtvm under test to the 1. 0 volt range.
E stablish a new 400 cps "reference level" by setting
to 0.90 on the 1 volt range.
11) Change the input signal
the
pli t ude to "reference level" established
Adjust capacitor C4 for a reading
If
12) Change the input signal to 4 mc and set the am­
plitude to the "reference level" established in step
10. The reading on the
be more than :1:2% of full scale from 0 . 9 0 .
Adjust R6 i n the input divider t o bring the 4 mc
response within ±2%.
several parallel resistors. IncreaSing the resistance
of R 6 will raise the frequency response at
Lowering the re sistance will decrease the 4 mc
response.
13) Switch the vtvm under test to the 3. 0 volt range .
E stablish a new 400 cps "reference level" by setting
to 0.90 on the 0 - 1 scale .
14) Change the input signal
plitude to the "reference level" established i n step
Adjust capaCitor
1
13.
0 . 9 0 on the vtvm under test.
L.
FINAL C HE C K
Repeat f'.e Basic Calibration procedures given in
paragraphs 4-7E and 4-7F.
if
4-8 TROUBLE SHOOTING
To assist in trouble shooting, a chart has been pre­
pared which lists various trouble symptoms, pos­
sible causes and/or remedies.
if
is of a more obscure nature than can be covered
by the chart, trouble can
by sectionalizing, and second by localization within
the
section by means of voltage and resistance mea­
surements. The circuit sections are indicated in
the block diagram (Figure 3-1).
1) The first step in sectionalizing is to check the
output of the regulated high-voltage supply: the dc
voltage between pin 1
sure 250 volts, ±5 volts.
H
the regulator output is not within these limits,
see paragraph 4-9.
IV
Sect. Page 9
to
20 kc and set the am­
step 10.
i n
of
O.
90.
vtvm
under test should not
This res istor consists
to
4 mc and set the am­
obtain an indication
to
C14
& ADJUSTMENT
If the
of
cause trouble
be
located by test: first
of
V7 and ground shOuld mea­
of
4 mc.
of