| Symptom: |
Unit immediately goes
into the protect mode when RF is applied. Only happens on specific
bands. Other bands are OK. |
| Probable
Cause: |
Defective
filter-switching relay in the low-pass filter. |
| Cure: |
Locate and replace the
bad relay. |
| Remarks: |
Generally, when the
relays fail, the armature winding shorts. This sometimes causes
damage to the relay driver IC9 chip on the main unit, align with the
associated chokes for that band. IC8 may also be damaged. |
|
|
| Symptom: |
Automatic antenna tuner
has one or more of the following symptoms: 1) Tuner drifts out of
tune unless a carrier is present. 2) Tuner goes through retuning
sequence each time PTT button is depressed, even after match had
already been found. 3) Tuner slows, but never settles on a 1:1
match. |
| Probable
Causes: |
1) Tuner needs
alignment. 2) Tuner requires installation of factory update. |
| Cure: |
Try adjusting R19 and
R25 trimmer pots in the main unit as per the alignment procedure on
page 5-10 of the service manual. If this doesn't help, contact
Technical Support regarding updates to the DET and Main units. |
|
|
| Symptom: |
Unit will not turn on.
No lights, no fan noise. A relay click can be heard from linear when
power switch in control head is pressed. |
| Probable
Causes: |
1) The circuit breaker
is tripped. 2) A cable is not connected. 3) No +8 volts is being
sent from exciter. 4) Power supply is blown. |
| Cure: |
Check to make sure
circuit breaker has not been tripped by turning it off, then on
again. Check again to make sure all cables are connected. If they
are, look for +8 volts DC at pin 1 of the DIN cable that plugs into
the 4KL. (The IC-781 had an internal fuse on this line). If the +8
volts is present inside the 4KL, remove the cover to the reg. unit
and look for obviously blown parts. If evidence of damage is
present, the reg. unit should be sent to one of our factory service
centers for repair. |
|
|
| Symptom: |
Unit immediately goes
into protect mode when switched to the 24 MHz band and above, even
in receive. |
| Probable
Cause: |
Unit has not been
out-of-banded for operation on 10 m and 12 m bands. |
| Cure: |
Call the Icom Technical
Support department for OOB mod info. |
|
|
| Symptom: |
Unit puts out normal
power but does not pass receive signal to transceiver. |
| Probable
Cause: |
Bad switching relay.
Possible bad relays are RL15 on filter unit, RL5 & RL6 in tuner
unit, and RL1 relay on the SPLTR unit. |
| Cure: |
Locate and replace bad
relay. |
| |
|
| Symptom: |
Unit produces noise or
"birdies" in the receiver on 40 meters and below. This
noise occurs as a "swishing" sound that moves up or down
the band. |
| Probable
Cause: |
Noise generated by the
internal switching power supply. |
| Cure: |
A modification can be
installed in the SPLTR unit in early production units to help
minimize the noise. Please contact Technical Support for a copy of
this modification. Also, we have found that wrapping the power cord
through a large ferrite toroid has alleviated the problem in some
units. |
|
|
| Symptom: |
IC meter reading is
high while power output is low in some bands. Protector meter
reading is OK. No components are overheating on the COMBINR unit. |
| Probable
Cause: |
Unit incorrectly senses
an over-current condition and is cutting the power back. |
| Cure: |
Tighten loose screws at
wire-wound resistor R11 on PA unit. If this does not help, try
performing the Ic meter and Ic ALC meter alignment on page 5-8 of
the service manual. |
|
|
| Symptom: |
Low output power with a
high Ic reading. Unit burns components on COMBINR unit. |
| Probable
Cause: |
Output power from PA
units are not equal. Possibly, there is a faulty pair of final
transistors. |
| Cure: |
Replace burned
components on the COMBINR unit. Disconnect and measure power output
from each PA unit individually. Locate and replace defective
components on PA unit(s) (finals, etc). |
| Remarks: |
Make a level check to
be sure that the four outputs from the SPLTR unit is the same for
each of the four PA sections. |
