| Symptom: |
Distorted RX/TX, or no
RX/TX on one or more bands. Distorted SSB audio; sounds raspy and
rough. Problem may be temperature related. |
| Probable
Cause: |
Bad trimmer capacitors
on PLL unit, HPL VCO section. |
| Cure: |
Replace plastic trimmer
capacitors C78, C88, C96, and C107 with ceramic equivalents. We
suggest using a 12 pf trimmer capacitor for C96 instead of a 7 pf as
listed in the service manual. This will allow you to properly adjust
the HPL lock voltage for that band. |
| Remarks: |
While you have the PLL
unit lifted, it would be a good idea to inspect and rework the
soldering in the regulator section. Also, inspect electrolytic
capacitors C128, C129, C132, and C137 in the regulator circuit for
discoloration caused by overheating. Replace all overheated
capacitors to prevent future failures. |
|
|
| Symptom: |
Frequency instability. |
| Probable
Causes: |
1) Unstable trimmer
capacitor C5 on 2nd L.O. unit. 2) Dirty RIT/XIT pot and switches. |
| Cure: |
Replace plastic trimmer
capacitor with a 30 pf ceramic trimmer and realign. Clean dirty
RIT/XIT pots and switches with Blue Showers solvent. |
| Remarks: |
Unstable C5 capacitor
is very common in the IC-745. The plastic version of this capacitor
should be replaced on all units that are in need of repair as
preventative maintenance. |
|
|
| Symptom: |
Erratic display i.e.,
frequency listed will be out of the normal operating range of the
radio. Rotating the VFO knob may cause strange characters to appear
in the display. Radio does not work properly. Cycling the power
switch a few times may restore operation temporarily. Problem may be
temperature related. |
| Probable
Causes: |
1) Cracked solder
connections on RAM unit is causing logic errors. 2) Program in RAM
unit is corrupted. 3) Burned/overheated R20 resistor on logic unit
is causing low voltage in logic unit. |
| Cure: |
Check for burned R20
resistor (10 ohm, 1/2 watt) on logic unit. If it looks OK, resolder
cracked solder joints at J1 and J2 connectors on RAM unit, then
reprogram. If this does not help, substitute RAM unit with a known
good one. If the substitute RAM unit works properly, then the RAM
unit must be replaced. |
|
|
| Symptom: |
RX noisy and
intermittent. Preamp intermittent. |
| Probable
Causes: |
1) Bad preamp relay on
RF unit. 2) Cracked solder on RF unit in preamp section. |
| Cure: |
Replace bad relay RL1
(FBR221DO12). Carefully examine the preamp section of the RF unit
for bad joints and resolder as needed. |
|
|
| Symptom: |
Intermittent low FM TX
output power. |
| Probable
Cause: |
Poor contacts in relay
RL1 on FM unit. |
| Cure: |
Replace bad RL1 relay
(221B-D009-M). |
|
|
| Symptom: |
No preamp operation.
Sensitivity of radio drops when preamp is engaged. |
| Probable
Causes: |
1) Bad preamp relay on
RF unit. 2) Burned components in preamp section on RF unit. |
| Cure: |
Replace bad RL1 relay
(FBR221DO12). Replace bad/burned preamp components on RF unit,
usually RL1 relay, Q11, Q12 transistors, R58 resistor, C86
capacitor, etc... Also check Q10 transistor for failure. If bad,
replace it with a 2SC2878B. |
|
|
| Symptom: |
Low, erratic TX output
in all modes. ALC meter reading is unsteady and may drop out
altogether. Removing the top cover may cause problem to disappear
for a while. Pressing on the wiring harness near the IF unit may
cause the power/ALC meter reading to fluctuate. Problem may be
temperature related. |
| Probable
Causes: |
1) Cracked solder
joints on IF unit. 2) Dirty RF power/mic gain pot. 3) Poor
connections at IF unit is causing low TX drive. This is sometimes
caused by oxidation at the point where the wires are crimped to the
connector pins. 4) Bad relay on FM unit (if installed). |
| Cure: |
Clean dirty RF
power/mic gain pot. Resolder cracked and suspicious looking solder
joints on IF unit. If these do not help, remove and resolder the
wire crimps in the RF connector pins in J2, J5, J12, J9, J19 and J20
connectors on the IF unit. Be sure to not add too much solder to the
connector pins or they will need to be replaced. Be sure all
connectors are fully seated after repair. Replace RL1 relay on the
FM unit. |
| Remarks: |
Although resoldering
the connector pins is a delicate and time consuming procedure, it
will save you a great deal of troubleshooting time and frustration. |
|
|
| Symptom: |
TX power marginal on
some bands. ALC meter reading is low but steady, not erratic. Cannot
use ALC to adjust for more power. Troubleshooting reveals that no
specific stage is malfunctioning |
| Probable
Causes: |
1) TX IF needs to be
aligned. 2) Modification to IF unit needs to be removed. |
| Cure: |
Set unit to 14.100 MHz,
TX in RTTY mode, and adjust L8, L10 and L11 coils on IF unit for
peak ALC meter reading. If this does not yield enough drive, remove
the 220-ohm resistor on the bottom side of the IF unit directly
beneath L8 coil and retune. Be sure to readjust power, ALC level and
metering, if needed. |
| Remarks: |
If the above steps have
no effect, troubleshoot for a defective TX stage, or follow steps
for curing erratic TX. |
|
|
| Symptom: |
VFO tuning is erratic,
sometimes skips when changing frequencies or bands. Displayed
frequency does not increment smoothly when VFO knob is turned
slowly. |
| Probable
Cause: |
Dirty rotary encoder. |
| Cure: |
Remove white plastic
cover from back of rotary encoder and spray clean the carbon track
with Blue Shower solvent. Spin VFO knob vigorously while spraying. |
| Remarks: |
Do not let solvent
saturate the display unit or allow it to come into contact with the
plastic display lens. Stuff a paper towel between the rotary encoder
and display unit to catch spray run-off. |
|
|
| Symptom: |
TX power gradually
drops off when warm. ALC meter indication remains at mid-scale.
Adjusting ALC does not help. |
| Probable
Cause: |
APC misalignment. |
| Cure: |
Realign ALC, Ic METER,
and APC as per pages 9-1 and 9-2 in the service manual. |
|
|
| Symptom: |
AC hum or buzz in
transmit and receive audio when an internal power supply is
installed. |
| Probable
Cause: |
AC in being induced
into the PLL from the AC wires and power supply case. |
| Cure: |
Twist the AC wires that
run from the rear panel to the power switch and route them away from
the PLL unit. Tape them up against the chassis if necessary.
Remarks: In some radios, especially older IC-745s, it is not
possible to completely eliminate all AC hum when using the internal
power supply. |
|
|
| Symptom: |
Drastic change in audio
frequency response between USB and LSB., i.e. USB audio has too much
bass while LSB audio has too much treble. TX frequency response is
also poor. |
| Probable
Causes: |
Misadjustment of the
BFO or PBT oscillator. |
| Cure: |
Align the BFO and PBT
oscillator as per page 9-4 of the service manual. |
|
|
| Symptom: |
Distorted/raspy-sounding
SSB TX. Complaints of RFI. Unit tests fine on dummy load. Unit is
being used with an external 3rd party power supply. |
| Probable
Causes: |
1) Inadequate station
ground. 2) External 3rd party power supply needs additional RF
decoupling. |
| Cure: |
Recheck station ground.
Improve if necessary. Install additional RF decoupling capacitors on
the DC terminals of the power supply. |
|
|
| Symptom: |
Noise in RX, birdies. |
| Probable
Cause: |
Voltage regulators on
PLL unit are oscillating. |
| Cure: |
Replace overheated
C128, C129, C132 and C137 regulator filter capacitors on PLL unit. |
|
|
| Symptom: |
No receive through LB
antenna jack. No BC band RX. |
| Probable
Cause: |
Open DS1 fuse on RF
unit. |
| Cure: |
Replace open fuse. |
|
|
| Symptom: |
1) No RX/TX at all.
Display normal. 2) No CW operation, or, 3) Some front panel controls
do not operate reliably. |
| Probable
Cause: |
Burned or open R1
resistor on reg. unit. |
| Cure: |
Replace R1 resistor
(4.7 ohm, 1/2 watt). |
|
|
| Symptom: |
TX
oscillations/spurious output. |
| Probable
Causes: |
1) Bad Q10 transistor
on RF unit. 2) Open parasitic-suppression resistor on PA unit. 3)
Bad electrolytic filter capacitors on PA unit. 4) Bad drivers or
finals. |
| Cure: |
Disconnect J9 connector
on the RF unit and see if the problem goes away. If it does, then
Q10 transistor is most likely bad (replace it with a 2SC2878B). If
disconnecting J9 connector has no effect, check the value of R22
resistor (4.7 ohms) on PA unit. This resistor may look OK but still
be open. Replace C18 and/or C25 capacitors if they appear swollen or
overheated. If none of the above are causing the problem and ALC
meter deflection is low, then most likely the drivers or PA
transistors are bad. |
| Remarks: |
Spurious output may
also be caused by incorrect band switch voltage to the low-pass
filter unit, or even faulty/burned components on the filter unit
itself. The above causes should be ruled out first, since low-pass
filter failures are not common in the IC-745. |
