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 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 versions. Remove excessive wax from around replacement
trimmers to prevent wax contamination. We suggest using a 12pf
trimmer for C97 instead of a 6pf 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.
R-71A
http://www.electronicsandbooks.com/eab1/manual/Hardware/I/Icom ...
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