HP 740B Operating And Service Manual page 36

Model 740B
filters, C1 and C2. The + and - 16.5 V Supplies
are referenced to
w·
(Wand ware electrically
common).
4-126. + 180 V, +360 V Power Supply,
plo
A8 (Fig-
ure 7 -12). The + 180 V Power Supply consists of
A8CR2
and A8C2which comprise a half-wave unregu-
lated supply. A8CR1 and A8C1 along with the + 180 V
Supply components form a voltage doubler for gen-
erating + 360 V. Both supplies are referenced toW.
( wand Ware electrically common). The output
of the + 180 V Supply provides operating voltages
for the Neon Drivers (p/o A8). The +360 V output is
fed out A8 pin 1 to the digital indicator tubes in Stan-
dard and Differential Voltmeter modes.
4-127. CHOPPERNEONDRIVERS,
p/oA8
(Figure 7-12).
4-128. METER LOOP NEON DRIVER.
4-129. The Meter Loop Neon Driver supplies a 95 Hz
square wave to the Meter Chopper neons A16DS1 and
A16DS2. The Meter Loop Neon Driver is a free-
running multivibrator consisting of A8Q1, A8Q2 and
associated components. A8R3 is adjusted to set the
multivibrator frequency to 95 Hz. A8R8* and A8R9*
are factory selected to set the range of adjustment
of A8R3. Paragraph 5-99 describes the procedure
01794-1
Section IV
for selecting A8R8* and A8R9*. The square wave
can be observed at A8TP21.
4-130. A16DS1 and A16DS2 are connected to opposite
sides of the multivibrator which causes them to flash
alternately. A16DS1 illuminates A16V2 and A16V4;
A16DS2 illuminates A16V1 and A16V3.
4-131. MAIN LOOP NEON DRIVER.
4-132. The Main Loop Neon Driver supplies pulses to
the Main Loop Chopper Neons, A17DSl and A17DS2.
A8Q3 and A8Q4 and associated components comprise
a free-running multivibrator. The frequency is ad-
justed to 162 Hz by A8R20.
4-133. A8Q5, A8Q6 and associated components act
together to shorten each of the square wave alterna-
tions from the multivibrator. The leading edge of the
positive half of the square wave from A8Q4 triggers
A8Q5 and A8Q5 conducts until A8CI0 discharges. The
discharge time occurs approximately half way through
the positive alternation of the square wave. When
A8Q5 conducts, Al7DS2 lights. A8Q3 and A8Q6 func-
tion in a similar manner. A17DSllights when A8Q6
conducts. This results in the neons lighting alter-
nately; but each neon goes out approximately 1. 5 msec
before the other neon lights.
4-11