Wavetek 3000 Instruction Manual page 78

MAINTENANCE
5- 8
imately as follows : -2 .5 VDC on +10 dBm
range with VERNIER fully clockwise ; -0 .7
VbC on 0 dBm range
with VERNIER fully
clockwise .
These voltages indicate
proper operation
of the meter board ;
while other values,
particularly posi-
tive voltages, indicate a defective IC
on the meter board . Next, check RF
power directly at 1110W output . If it
is correct, the trouble lies in the
attenuator or its RF cables . If module
M10W output is low, measure RF level
directly at module M9W output - this
should be approximately -10 to -11 dBm .
If this level
is correct, module M10W
is defective ; while if the level is low,
Sweep Oscillator M9W is defective .
OUTPUT METER DOES NOT MOVE - If meter
is pegged at either end of scale, the
trouble is probably a defective meter-
driver IC on meter board (C315) . If
meter remains at mechanical zero, meter
movement may be open or a meter-board
IC is defective .
UNLEVELED LAMP ON - RF OUT connector not
terminated in 50-ohm load, AM percentage
set so that peak of modulated
output
exceeds +13 dBm, defective module M10W,
defective attenuator or connecting RF
cables .
Connect power meter directly to M10W
output . Set OUTPUT dial and VERNIER
for a +13 dBm reading on power meter at
50 .000 MHz . Step through frequency range
from 10 to 520 MHz in 10 MHz-steps . A
power meter reading of +13 dBm ±0 .5 dB
with UNLEVELED lamp OFF indicates proper
operation of module M10W . Connect power
meter directly to attenuator output and
repeat above steps . If attenuator output
is correct, trouble is due to a defec-
tive RF cable or possibly a poor ground
connection at RF OUT connector . If out-
put is correct at MlOW but the UNLEVELED
lamp is ON, the trouble is probably a
defective lamp-driver circuit in module
M10W .
ACCURACY LAMPS FLASH CONTINUOUSLY - A
steady light in CW mode but flashing
lights in FM modes indicate a defective
M29-1 or M33 module . If ACCURACY lamps
flash in all modes, one or more of the
phase-locked loops is open ; see PHASE
LOCKED LOOP TROUBLES below . NOTE : Above
the normal frequency range of the instru-
ment (in the vicinity of 560 MHz), it is
normal for phase-locked loop #4 to un-
lock causing the lamps to flash .
PHASE-LOCKED LOOP TROUBLES - An open or
unlocked loop, indicated by a lighted
module lamp,
can be caused by a number
of factors, including : low AC-input vol-
tage, low DC-supply voltages, improper
phase-locked loop DC voltages, an open
or shorted RF cable or a defective mod-
ule .
A defective RF cable or module can have
a chain-reaction effect that causes
two or more loops to unlock . For example,
loss of the 1 kHz signal to module M31
will cause PLL #1 to unlock ; thus, module
M31 may not supply a proper signal
to
module M34, causing PLL #4 to unlock .
Failure of the 40 MHz crystal oscillator
in module M30 will cause all four loops
to unlock, since all six reference fre-
quencies will be lost .
Table 5-2 lists typical RF signal-input
levels for each of the phase-locked
loops . Those signals having a TTL level
or 1 V level may be measured with a high-
frequency oscilloscope ; the other signals
are best measured with a spectrum analy-
zer . NOTE : The TTL waveform shown in
Table 5-2 is for illustration of voltage
values only, and does not necessarily
represent the observed waveshape .
Phase-Locked Loop#1 - Unlocking of this
loop maybe caused by a defective module
M31, module M30 or RF cable connecting
M30 to M31 .
If M31A unlock indicator is on, check 1
kHz signal as listed in Table 5-2 . If
1 kHz signal is correct, module M30 is
operating properly, then check RF cable
between M30 and M31A . If proper 1 kHz
signal is being applied to M31A, check
for 7 .3 V on pin 6, +18 V on pin 7, and
-18 V on pin 8 of M31A, If input signal