Symptom: |
Dead radio. No lights,
no sound, no display. |
Probable
Cause: |
No 13.8 output from
P.S. |
Check: |
Make sure the external
DC jumper is installed on the rear panel. If it is, remove and hook
up 13.8v from external supply. If unit powers up with external
power, check regulator unit for faulty or open F1 fuse. If unit
remains dead, and 13.8v line is not open, check for faulty IC9 timer
IC on Logic A unit. |
Remarks: |
Unit draws
approximately 3 A at 13.8V DC. |
|
|
Symptom: |
Logic problem--erratic
frequency change, front panel push buttons locked-up, logic check
shows address fault. CPU reset does not help. |
Probable
Cause: |
CPU address problem. |
Cure: |
Install W1 jumper into
J7 on SW-D unit. J7 is located on left side PCB beneath access door
in top cover. Then reset CPU. (Push and hold [CLEAR] and turn unit
on.) |
|
|
Symptom: |
Intermittent CRT
display. Various problems. Receiver operation is normal. |
Probable
Cause: |
Cracked solder on CRT
unit PCB. |
Cure: |
Resolder every solder
joint on CRT unit PCB. |
|
|
Symptom: |
Intermittent excessive
CRT brightness. Vibration sensitive. Receiver operation is normal. |
Probable
Cause: |
Intermittent negative
brightness control voltage. |
Cure: |
Resolder cracked solder
joints on VR-C unit. If still bad, resolder all solder joints on CRT
unit PCB. |
|
|
Symptom: |
Intermittent whine or
hash noise in FM from 30-499 MHz and 1000-1499 MHz when warm. Noise
is most often heard in FM broadcast band. |
Probable
Cause: |
Temperature sensitive
768 MHz VCO on PLL B unit. |
Cure: |
Replace faulty IC15
(768 MHz VCO) on PLL B unit. |
|
|
Symptom: |
Receive problems from
500-999 MHz, and 1000-1499 MHz. |
Check: |
268 MHz VCO section on
PLL B unit. |
|
|
Symptom: |
No RX at all above 30
MHz, all modes. Green LED is off. |
Probable
Cause: |
PLL unlock. |
What
to do: |
Check LPL injection to
HPL (starting at Q15 transistor) on PLL B unit and trace to fault
from there. Note that the reference oscillator, DDS, LPL sections
are probably okay since HF is working. If the PLL section has
recently been serviced, check for loose coaxial connectors. |
|
|
Symptom: |
Low RX from 30-1000 MHz
and/or 1-2 GHz. |
Probable
Cause: |
Spread out center
conductor at N-connector on rear panel. Caused by forcing on a
PL-259 connector. |
Cure: |
Straighten center
conductor or replace connector. |
|
|
Symptom: |
No RX, all bands, all
modes. Green RX light not on, radio very quiet. Display and front
panel operation are normal. |
Probable
Cause: |
PLL unlocked. |
Check: |
Check power supply
voltages to PLL unit. If okay, check reference oscillator output on
PLL B unit. If there is no reference, replace reference oscillator
(crystal oven). If reference is okay, start at DDS unit and work
your way out to HPL. |
|
|
Symptom: |
No HF RX at all. Not
PLL unlock. VHF and UHF operation normal. |
Common
Cause: |
Hi-Z antenna switch on
rear panel is in the wrong position. |
Less
Common: |
No HF 2nd L.O. output.
Check area of Q12 and Q13 transistors on PLL B unit for 38.XX MHz.
2) Open diode on RF A unit. 3) No band switching of supply voltages
to IC1 and IC2 ICs on RF A unit. 4) Disconnected coax to or from RF
A unit. |
|
|
Symptom: |
Blank screen when
receiving TV signals in display mode. |
Probable
Cause: |
Video in/out jumper is
missing from rear panel. |
Remarks: |
Sometimes it is
necessary to turn up CRT brightness for adequate picture when
receiving TV signals. |
|
|
Symptom: |
Squelch erratic. AF
gain control and squelch control interact. RX may be low. S-meter
may not zero in absence of signal. |
Probable
Cause: |
Low or negative supply
from reg. unit. |
Check: |
Verify proper voltages
at J8 connector on reg. unit. Pay specific attention to levels of
-12 V and -7 V on pins 4 and 5, respectively. |
Cure: |
If voltages are absent
or low, electrolytic capacitors in DC-DC converter section are
probably old. Replace all electrolytic capacitors in DC-DC converter
(shielded) section. |
|
|
Symptom: |
Center frequency
displayed on spectrum scope jumps far away from center when changing
display resolution. |
Probable
Cause: |
Scope unit is out of
alignment. |
Cure: |
Perform Center
Frequency, Horizontal Scale, and AFC Center alignments on page 5-14
of service manual. Sweep oscillator may also require adjustment. |
Remarks: |
Make sure that AFC
switch on scope unit is in correct position. |
|
|
Symptom: |
Voice operated squelch
operation is unreliable. Unit sometimes passes up signals when
scanning. |
Probable
Cause: |
Discriminator
misalignment. |
Cure: |
Perform center meter
alignment on page 5-10 of service manual. Voltages are critical and
must match listed values very closely. |
|
|
Symptom: |
Marginal, low, or no RX
in specific sections: HF, VHF or UHF bands. |
Probable
Cause: |
RF overload has damaged
front-end. Check sensitivity in these sections:
30-89 MHz, go to Q1 section on RF B unit if bad
90-249 MHz, go to Q2 transistor
250-499 MHz, go to Q3 transistor
500-999 MHz, go to Q4 transistor
HF only: go to bandpass filters on RF A unit. |
Cure: |
Replace defective
components in faulty sections. May require realignment of varactor
diodes. |
Remarks: |
If low or marginal
VHF/UHF RX is experienced at edges if one of these sections only, an
alignment of that section may be all that is needed (see page 5-8 of
service manual). Before attempting alignment, be sure that negative
voltages from the regulator unit are correct, especially in older
units with many hours of use on them. |
|
|
Symptom: |
Marginal or low RX on
all bands of VHF and UHF spectrum with especially poor RX at the
edges of some bands listed above. |
Probable
Cause: |
Low or noisy reg. unit
voltages are detuning front-end varactors diodes. |
Cure: |
Check output voltages
from reg. unit for proper value and for noise. If okay, check for
faulty D1 and D21 diodes on RF B unit. If bad, replace faulty
electrolytic capacitors in reg. unit. Realignment of RF B unit
should not be necessary. |