ICOM机器常见问题和解决办法（英文谨入） [复制链接]

symptom:
no tx output.

probable cause:
bad q32 transistor on rf unit.

cure:
replace q32 transistor (2sc4673d) on rf unit. also check for leaky d37 diode (ma862) on rf unit.

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symptom:
raspy rx audio when warm, sounds like intermodulation.

probable cause:
leaky d37 diode on rf unit.

cure:
replace d37 diode (ma862).

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symptom:
tx led indicator does not light.

probable cause:
r105 resistor on sw-a unit has been knocked loose during shipping.

cure:
replace or resolder r105 resistor (1.8 k)

remarks:
r105 resistor is a surface-mount component.

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symptom:
harsh tx cw note.

probable cause:
unit needs factory update.

cure:
change value of tantalum capacitor c18 on if unit to 3.3 礔, 16 v.

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symptom:
radio is dead, does not power-up. radio powers up if vcc line to pa is disconnected.

probable cause:
shorted pa fets.

cure:
replace both pa fets.

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symptom:
display dims in cw tx when af volume is turned up.

probable cause:
unit requires factory update to logic unit.

cure:
contact icom technical support for update procedure.

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symptom:
in a brand new radio, rotary encoder shaft does not turn smoothly; feels rough.

probable causes:
shipping damage to rotary encoder.

cure:
replace rotary encoder.

symptom:
any intermittent problems, including intermittent rx, tx, display, power up, and noisy rx/tx.

probable cause:
regulator unit problems. heat and age is causing the regulator unit to produce unstable voltages to the radio.

cure:
recondition regulator unit: lift reg. unit pcb and rework all overheated and suspicious-looking solder joints (you may find a lot of bad joint to solder on an old unit). repair cracked or damaged foil trace at l7 choke, if needed, and apply rtv compound between l7 choke and neighboring components to prevent it from coming loose again. resolder joints at current-sensing resistor bar r22. replace these commonly overheated components: l11 coil, c4, c28 capacitors, and r35 resistor. (for l11 coil, a type lw-16 choke may be substituted for the lw-15 for increased reliability.) examine the top side of the reg. unit carefully for more overheated components. replace all (formerly) blue electrolytic capacitors that have turned brown with heat and age. be thorough. clean board once repairs are completed and examine your work. apply fresh thermal compound to heatsink-mounted components.
remarks: because it runs hot, the regulator is a common source of trouble in the ic-781, especially in those units with many operating hours. we strongly recommend inspecting the regulator unit on all ic-781 that are in need of repair before any other repairs are commenced.

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symptom:
intermittent low or no rx/tx output. radio is vibration sensitive. symptoms may disappear when radio is turned upside-down or when bottom cover is removed.

probable cause:
cracked solder joints at crystal filters in if unit.

cure:
resolder filters.

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symptom:
no tx output. pa is not drawing any current in tx mode.
probable cause: no 32 volts to pa unit from reg. unit.

cure:
resolder cracked solder joint at l7 choke on reg. unit and secure it with rtv to prevent it from shaking loose again.

remarks:
while reg. unit is lifted, it would be a good idea to service it as outlined above.

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symptom:
unit shuts down when tx power is turned up.
probable cause: premature over-current shut-down.

cure:
resolder cracked joints at r22 current sensing resistor on reg. unit.

remarks:
while the reg. unit is lifted, it would be a good idea to service it as outlined above.

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symptom:
birdies, whistles, and/or hash noise in rx, especially on lower bands.

probable cause:
reg. unit is running noisy.

cure:
resolder all suspicious looking solder joints on reg. unit. replace overheated c24 capacitor and l11 coil in reg. unit.

remarks:
while the reg. unit is lifted, it would be a good idea to service it as outlined above.

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symptom:
r20 resistor emits a small puff of smoke when radio is first powered-up, especially if radio has been turned off for a while. radio seems to work properly.

cure:
do nothing. this is a normal occurrence and does not mean there is a reliability problem in the radio.

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symptom:
radio is dead, no lights, no display, no sound.

probable causes:
1) open timer relay on pi unit. 2) open r20 resistor (3 ohm, 2 watt) on pi unit. 3) open start-up relay on pi unit. 4) unit plugged into 110v when it is configured for 220v operation. 5) bad timer ic on logic a unit. 6) cracked solder joints in reg. unit. 7) shorted rectifier d1 on pi unit. (this causes r20 resistor and main fuse to blow.)

cure:
correct as needed.

remarks:
if r20 resistor on pi unit is burned, there may be failure on the reg. unit. also, mount replacement r20 away from the pcb to prevent it from ruining the pi unit should it ever burn again.

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symptom:
power output is too high (around 250 watts). front panel rf power control and internal alc adjustment have little effect.

probable cause:
bad detector components on filter unit.

cure:
replace d8 & d9 diodes (both 1k60) on filter unit. check l17 coil.

remarks:
check filter unit for overheated components.

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symptom:
no tx power output. inspection reveals that electrolytic capacitor c11 on ps unit has exploded.

probable cause:
biasing problem at driver transistors- base voltage is higher than .68 volts.

cure:
replace all obviously burned components on pa unit, including driver transistors. make sure vcc to pa unit is around 33 volts. if ok, disconnect vcc drivers and measure base voltage. if over .68 volts, replace d1 & d3 diodes (mv5 & 1s953). realign driver and pa idle current.

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symptom:
no or low tx power output on one or more bands. pa-ic meter reading is high on faulty bands.

probable cause:
burned components on filter unit, usually toroids or relays.

cure:
replace faulty components and check the automatic tuner for a possible problem. verify that the power output from the radio is not more than 160 watts.

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symptom:
no rx/tx on 20 khz of each 500 khz tuning step, especially when radio is
cold or first powered up.

probable cause:
pll unlock.

cure:
adjust dds-lpl in both pll a and b units for proper lock voltage.

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symptom:
constant tone in speaker when in cw mode. unit goes into tx automatically in cw mode when vox button is pressed.

probable cause:
shorted cw key line.

cure:
replaced shorted rf filter fi-103 on connector 2 unit, and/or shorted f11, f12 and f13 filters on phones unit.

remarks:
use shielded cable to cw key to prevent future occurrences of same problem.

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symptom:
ac hum or buzz in tx audio.

probable cause:
poorly shielded or improperly shielded cable is hooked up to accessory jack in back of radio.

cure:
advise customer to replace cable and have accessory checked for faulty ground.

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symptom:
intermittent crt display problems such as loss of vertical hold, raster with picture, or complete blacking out.

probable causes:
1) unsteady 13.8 volts or video signal to crt unit. 2) bad solder joints on crt unit pcb.

cure:
verify steady and clean 13.8-volt supply at pin 1 of dc power connector on crt unit. if this is ok, resolder cracked solder joints in crt unit pcb.

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symptom:
crt displays garbage or incorrect characters. radio seems to work fine, otherwise.

probable cause:
bad crtc unit on logic a unit.

cure:
troubleshoot and replace defective components on crtc unit. most common problem is one of the ram chips has gone bad: ic3, ic4, ic5 or ic6.

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symptom:
computer control does not operate in "transceive" mode.

probable cause:
unit is configured for deft (default) in ci-v set mode.

cure:
in the ci-v set menu, change setting from deft to user mode.

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symptom:
ci-v control-unit does not communicate with computer. inspection reveals that no ttl signal is present at the remote jack when the vfo knob is turned.

probable cause:
bad i/o transistors on logic unit.

cure:
replace bad q3 and q4 transistors (both 2sc2458gr) on logic a unit.

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symptom:
antenna tuner can't find resonance on some bands. both motors turn when tuner hunts.

probable causes:
1) presets far out of adjustment. 2) burned variable capacitors c303 or c304. 3) burned relays on at tuner board. 4) bad relay rl1 on at controller board.

cure: connect radio to a dummy load and try adjusting presets. if a low swr cannot be reached by manual tuning, then most likely there are burned relays or capacitors on the tuner unit. if unit is able to find a tune in the preset mode but de-tunes in the automatic mode, then either rl1 relay is bad on the controller unit, or there is a problem with the tuner swr detection circuitry.

remarks:
check for overheated rf switching components on the connector 2 unit near the antenna connector.

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symptom:
antenna tuner doesn't tune on any band. inspection reveals one of the motors is not turning.

probable causes:
1) jammed motor gear assembly. 2) tuning capacitor plate has warped from heat and is now jamming motor. 3) blown motor driver transistors.

cure:
be sure that the motor is not jammed into one end of its tuning range. the motor can be unstuck by applying external dc directly to the motor itself. (15 volts is usually enough. disconnect j1 connector before applying voltage to prevent damage to the controller unit.) if the motor is not stuck, then the problem is most likely bad motor transistors. these overheat when they go bad, so damage to the board will be obvious.

remarks:
if the motor drivers are blown, the ic6 (5-volts) regulator on the tuner unit may also be bad.

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symptom:
clock does not hold time.

probable cause:
dead or weak clock battery.

dure:
measure lithium battery bt1 in circuit on logic b unit (top unit). if it measures less than 2.8 volts, replace it.

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symptom:
scope is inoperative, or radio does something unusual (such as loses rx) when scope is activated. problem disappears when scope unit is lifted or bottom shield is removed.

probable cause:
excessively long leads on bottom side of scope unit are shorting to shield.

cure:
trim leads so they do not short against shield.

remarks:
pay special attention to the leads around the outside edge of the board. these are outside the insulator inside the bottom shield.

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symptom:
no audio from headphone jack.

probable cause:
burned components on phones unit, most likely caused by rf feedback.

cure:
replace burned r1 and r2 resistors (10 ohms) with 1/2 watt versions. check l8 and l11 coils.

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symptom:
noisy fan; rattles at some speeds.

probable cause:
faulty bearings in fan.

cure:
replace fan. fan cannot be lubricated or serviced.

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symptom:
intermittent static noise in either a or b vfo channel, or no rx at all in either a or b vfo channel. check reveal that both a and b pll's are locked, and 1st l.o. injection signal is present and clean at j4 and j10 connectors on rf unit.

probable causes:
bad solder at mixer fets on either a or b channel. in the case of no rx, mixer fets q2 & q3 may be bad.

cure:
resolder cracked joints in failed mixer unit mounted to rf unit. replace faulty q2 & q3 fets (both 2sk125), and burned l7 coil.

remarks:
board runs hot around mixer section. look for poor solder joints on this area on this fets.

symptom:
intermittent/no rx/tx. display reads "_______".

probable cause:
pll unlock.

cure:
replace bad x1 crystal oscillator on pll unit.

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symptom:
some front panel controls on left side do not work (mode switch, lock switch, etc).

cure:
rework bad or cracked solder at j1 connector on sw-a unit.

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symptom:
unit stuck in tx mode.

cure:
replace bad q40 transistor on main unit.

symptom:
any of the following: cannot change band to uhf, no uhf volume or squelch control, no uhf tuning, or strange-sounding beep tone.

cure:
rework bad soldering at j3 connector on display unit and replace the sw-b board with a factory-modified flex pc board.

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symptom:
no audio output from receiver.

cure:
remove excessive solder on the main-a unit near the audio amp.

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symptom:
howling if volume is turned up when using uhf.

probable cause:
microphonics in vco section.

cure:
resolder the ground spring at the uhf vco shield. you may also add a second spring for further improved resistance to microphonics

symptom:
on the control head, cannot change bands on either vhf or uhf, no volume or squelch control, or no tuning control. microphone control ok from mic.

probable cause:
cracked solder connections on the smd connectors between the front panel controls and the display board.

cure:
repair bad soldering at j3 and j4 connectors on the control unit and/or j1 connector on the sw-a and sw-b units.

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symptom:
no transmit on either band.

probable cause:
cracked solder connections on the smd connectors between the microphone connector board and the logic board.

cure:
rework bad solder at j4 connector on logic unit and/or j2 connector on mic unit.

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symptom:
no audio output from receiver.

cure:
rework bad soldering at the ext spkr jack on the main-a unit.

symptom:
cannot turn on or off, no volume control, no tuning control.

probable cause:
cracked solder connections on the connectors between the front panel control pots and the circuit board.

cure:
repair bad soldering at j4 and j5 connector in logic unit and/or j1 connector on sw-a and sw-b unit. replace sw-a and sw-b unit with factory-modified flex pc boards.

symptom:
weak rx, sometimes weakness varies. alignment does not help.

probable cause:
leaky tantalum capacitor.

cure:
c80 tantalum capacitor (1 礔, 35 v) on the receiver unit may be installed backwards. the pcb silk-screening is incorrect. replace the capacitor with a new one.

symptom:
no rx/tx on 440 mhz band. dashed lines on display.

probable cause:
pll unlock.

cure:
lpl loop on the pll-b unit is out of alignment and/or unstable. replace the plastic trimmer capacitor with a ceramic 12 pf trimmer capacitor and realign.

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symptom:
extremely low or no tx power output.

probable cause:
broken solder connection at j2 connector on apc board.

cure:
repair solder connections. reposition apc board upward to reduce stress on connector to prevent future failure.

ic-f30, ic-f30lt, ic-f40 and ic-f40lt

symptom:
won't turn on / no display.

probable cause:
poor connection at front cover flex cable to main board.

cure:
polish flex cable contact area with a clean pencil eraser. remove all eraser residue. reconnect the flex cable.

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symptom:
no tx/rx, flashing dots (on lt version), flashing led (on simple version).

probable cause:
hidden system data has been lost.

cure:
clone from a working radio to computer and save the file. clone the file to a non-working radio to restore data.

ic-m80, ic-m100 and ic-m120

symptom:
no tx, poor rx sensitivity.

cure:
resolder cracked solder joints in vco section.

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symptom:
no rx/tx.

probable cause:
pll unlock.

cure:
repair cracked solder in vco sections.


ic-m56
symptom:
flashing display.

probable cause:
pll unlock.

cure:
repair cracked solder in vco sections.


ic-m125
symptom:
various logic-related symptoms including stuck in ic mode, no display, etc...

probable cause:
blown ic22 chip.

cure:
replace ic22 chip.

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symptom:
when dial is pressed, radio goes to channel 70.

probable cause:
lithium battery is shorting to radio.

cure:
replace ic22 chip.

ic-r71a

symptom:
radio is dead; no display, no lights. problem may be intermittent.

probable causes:
1) cracked solder joints on regulator unit. 2) loose board mounting screw on the regulator unit that provides ground to the board. 3) cracked solder joint(s) where power transformer mounts to regulator unit.

cure:
remove the regulator unit from the radio and resolder all suspicious solder joints on the regulator unit. pay particular attention to the solder joints at heat sink-mounted transistor q1 on the regulator unit.

modification:
after tightening the regulator unit to the chassis, at the chrome screw with the spacer, apply a solder bridge across the spacer to form a solid electrical connection between the board and the chassis. this will prevent future failures due to bad connections at this joint.

remarks:
the power supply on the r-71a receiver runs very hot, and problems with the regulator unit are common. we recommend inspecting and servicing (if needed) the regulator unit in all r-71a receivers that are in need of repairs.

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symptom:
ac hum in audio; radio may seem to vibrate during operation; pilot lamp may be dim. inspection reveals excessive ac ripple on 13.8 line in radio.

probable causes:
bad bridge rectifier d1 on regulator unit.

cure:
replace bad d1 bridge rectifier (kbpc102). service regulator as per previous cure.

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symptom:
ac hum in audio after cr-64 crystal oscillator is installed.

probable causes:
the oven in the cr-64 crystal oscillator is drawing more current than the reg. unit can handle.

cure:
service the power supply as listed above. on older production units, check resistor r2 on the reg. unit. if it is 100 ohms, replace it with a 56 ohm, 5 watt. adjust the reg. unit output voltage to 13.6 volts.

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symptom:
no audio. s-meter fully deflected.

probable causes:
-10 volt dc-dc converter failure.

cure:
replace faulty dp-2 module (ic-6) on the matrix unit.

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symptom:
frequency display blanks out periodically with only decimal points remaining.
probable cause: display dc-dc converter has noisy output.

cure:
replace all of the following dried-out electrolytic capacitors on the display unit: c15, c16, c17, c18, c19, c20, c21 and c22. these capacitors are bright yellow when new. if they have turned brown, they are old and dried out.

remarks:
while servicing the dc-dc converter section examine the board closely for cracked solder joints as this section of the radio runs hot. also, we recommend reprogramming the ram card after servicing the dc-dc section.

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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. cycling the power switch a few times may restore operations temporarily.

probable causes:
1) cracked solder connections on ram unit is causing logic errors. 2) program in ram unit is corrupt.

cure:
resolder cracked 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. if the substitute ram unit does not cure the problem, there may be noise from the dc-dc converter causing the logic unit to glitch. follow instructions for the previous problem.

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symptom:
noisy rx on most bands. noise seems to be internally generated and is present whether or not an antenna is connected.

probable causes:
dried out capacitors c128, c129, c130 and c137 on pll unit are causing the 5 and 8 volt regulators to oscillate.

cure:
replace capacitors. most of these capacitors are light blue when new. if they have turned brown or gray, they are old and dried out.

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symptom:
garbled ssb audio on one or more bands. audio may cut out altogether. some bands may sound ok. problem may be temperature related.

probable cause:
bad trimmer capacitors on pll unit, hpl vco section.

cure:
replace plastic trimmer capacitors c78, c88, c97, and c107 with ceramic equivalents. remove excessive wax from around replacement trimmers to prevent wax contamination. we suggest using a 12 pf trimmer capacitor for c97 instead of a 6 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, rework cracked solder around the regulator section and at the two ground springs.

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symptom:
very low sensitivity on all bands.

probable causes:
1) open rf fuse f1 located at antenna jack. 2) bad fets on rf unit, probably caused by an rf overload through the antenna jack.

cure:
check for open fuse. replace q3 & q4 mixer fets on rf unit.

remarks:
if there is 6 volts present at the center conductor of the antenna jack, unit has taken an rf overload. see next problem.

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symptom:
marginal sensitivity, or sensitivity is reduced when coax shield is connected to the antenna jack. inspection reveals 6 (or 9) volts dc at center if the antenna jack.

probable cause:
rf overload through the antenna jack has shorted capacitors on rf unit.

cure:
replace shorted c1 capacitor (0.047 礔, 16v) on rf unit. also check c7 and c11 capacitors for shorts.

remarks:
for future reliability, you may wish to replace a leaky c1 capacitor with a 50-volt version.

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symptom:
buzz in audio. buzz can be heard in speaker or headphones even with volume control set to minimum.

probable cause:
audio cables are too close to the ac wires.

cure:
reroute ac wires and audio cables away from each other behind front panel in power switch area.

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symptom:
cpu noise in audio. noise may be louder on some bands than others.

probable causes:
1) poor ground on display unit. 2) inadequate shielding for rf unit.

cure:
make sure that audio cables and rf unit control lines are not routed next to cpu control and display data lines. try tightening the two screws beneath the display unit pcb. if neither of these help, install a plastic coated metal shield over the display unit. this type of shield is available through our parts department.

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symptom:
loud, high pitched squeal emanates from inside radio.

probable cause:
dc-dc converter transformer has a loose core.

cure:
replace t1 transformer (to-9) on the display unit.

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symptom:
vfo tuning is erratic, sometimes skips when changing bands. sometimes least-significant digit in display doesn't 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 and display unit to catch spray run-off.

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symptom:
no rx through ant 1 (lba) jack.

probable cause:
open fuse ds2 on rf unit.

cure:
replace open fuse.

symptom:
radio is off frequency.

probable cause:
2nd l.o. needs alignment.

cure:
align l39 coil on pll unit: set displayed frequency to 511.9999 mhz and adjust l39 coil for 768.0000 mhz at j6 test point on pll unit.

remarks:
this is a common problem in the ic-r7000. we recommend that the 2nd l.o. frequency be checked on all ic-7000s that are in need of repair.

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symptom:
no digital display when the radio warms up.

probable causes:
1) faulty dc-dc converter on display unit. 2) bad solder at flex cable between display unit and ds1 display.

cure:
replace dried-out electrolytic capacitors in display unit. resolder cracked joints at display flex cable.

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symptom:
low rx on all bands.

probable cause:
incorrect voltages from dc-dc unit.

cure:
check for correct output voltages at j2 connector of the dc-dc board. replace c1 and c2 capacitors (both 33 礔, 16v) on the dc-dc unit if voltages are incorrect.

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symptom:
distorted audio in fm mode, especially as unit warms-up.
probable cause: bad capacitor on if unit. unit needs update.

cure:
replace electrolytic capacitor c135 on if unit and update if unit: install a 100 k resistor between the negative side of c135 capacitor and ground.

symptom:
no receive at all.

probable cause:
pll unlock.

cure:
replace faulty c69 capacitor on pll unit.

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symptom:
no receive at all on same bands after warm-up.

probable cause:
pll unlock.

cure:
bad solder connections and/or bad q1 or q3 transistors in vco unit.

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.

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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.)

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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.

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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.

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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.

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symptom:
receive problems from 500-999 mhz, and 1000-1499 mhz.

check:
268 mhz vco section on pll b unit.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

ah-2, ah-3 and at-120


symptom:
won't start tuning.

probable cause:
faulty regulator.

cure:
replace faulty ic9 8-volt regulator chip.

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symptom:
won't start tuning.

probable cause:
start line goes low, but key line remains high.

cure:
replace faulty q2, q3, or q4 transistors.

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symptom:
won't tune on some bands.

probable cause:
faulty ic10, ic11, or ic12 chips.

cure:
replace faulty ics.

remarks:
check resistor-cap pairs next to relays for signs of overheating.

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symptom:
in ah2 controller: "tune" and "thru" leds don't work.

probable cause:
faulty ic1 chip and/or ic2 5-volt regulator.

cure:
replace defective parts.

感谢楼主提供的好资料