| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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 µF, 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| 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. |
|
|
| Symptom: |
No RX through ANT 1
(LBA) jack. |
| Probable
Cause: |
Open fuse DS2 on RF
unit. |
| Cure: |
Replace open fuse. |
