of V11 (should total 99 ma). If voltage is too high try re-
placement for V12. If voltage is erratic try replacement
of V13.
d. To check the operation of the regulated supply, operate the
instrument from a variable transformer. Slowly vary the
supply voltage from 103 to 127 volts. If the 225 volt supply
varies appreciably, one or more tubes need replacement.
If the 225 volts rises when the instrument is operating at
103 volts, V12 is weak. If the voltage drops, V10 and/or
V11 needs replacement. Poor regulation at 127 volts is
usually due to a weak V11 or possibly V12.
~
WARNING: Always re -set the filament oscillator voltage after
the t225V is adjusted. See below.
To adjust the '5.4-volt rms square-wave heater voltage proceed as
follows :
a. Connect an average responding a-c voltmeter which is
calibrated in terms of rms of a sine-wave, such as an
@400D, to terminals 4 and 6 of transformer T2 (see
Figure 18). The meter should read 6 volts, which is equal
to 5.4 volts rms. Note: If a peak responding meter, such
as a vtvm with a diode probe is used, a spurious reading
will probably be obtained due to spikes, etc., in the
square-wave signal. This type of instrument should be
avoided. An accurately calibrated multimeter with full
wave rectifier for a-c measurements is also suitable, as
this type of instrument is average responding. If necessary
adjust potentiometer R55 to obtain a reading of 6 volts.
I b. If the voltage cannot be adjusted to 6 volts (5.4V rms)
and is too low, try a replacement for V9 and check the
load current drawn from the secondary winding. Load
current should not exceed 0.6 ampere.
c. Always check this voltage if the t225V supply is adjusted,
as any change in the t225V will affect the filament
oscillator output.
The +33O-volt, -730-volt outputs vary with line voltage and are
nominally 330 and 730 volts when the line voltage is 115 volts. If
the t330-volt supply is too low, try replacement V10, C43a, C43b,
and check the total load current, 106 ma., (3. 5 ma to 330 volt line
102 ma to regulator).
If the -730-volt supply is too low, check the two selenium rectifiers
on the back of the left-hand resistor board. These are very small
units which resemble film type resistors in appearance. After dis-
connecting one side of each rectifier from the circuit, the forward
resistance can be masured with a suitable ohmmeter. Due to the
large number of cells in series in these units, an ohmmeter with a
large open-circuit voltage will give a better reading. Using a typical
multimeter-ohmmeter equipped with a 30 volt internal battery, the
forward resistance should read less than approximately 200,000 ohms
4-3 |
ACEC
HEWLETT-PACKARD
