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6.9
Lack of crispness in transmit audio
Cause: The RF-bypass capacitor, at the collector of the 1st audio amplifier, is so large that it
bypasses the higher audio frequencies along with the RF. {The amount of treble-rolloff in a
stock radio is about 4.5db at 2800Hz.}
Fix: On the IF Unit, at Q19, change C106 from .015µF to approx. 0.001µF. Q19 can be found
directly behind the filter space for the larger of the two, optional CW-filters.
6.10
No power output on most bands
Cause: This is usually due to the final unit bandswitch being out-of-sync with the bandswitch
shaft. This problem is caused by a cracked, plastic shaft-coupling between the RF unit and the
final unit. Trio-Kenwood did not use Locktite, or a similar thread-locking compound, so the
setscrews in the coupling had to be over-tightened, by the assembler, to prevent the setscrews
from loosening during operation. The constant stress on the plastic, caused by the combination
of ordinary use and the over-tightened the setscrews, eventually causes the plastic couplings to
crack.
Fix: Remove the cracked plastic coupling and either epoxy it together, buy a replacement
coupling from Trio-Kenwood, or find a replacement shaft coupling made from metal. Use
Locktite in the setscrew threads during re-assembly so that the set-screws will not need to be
overtightened. Plastic shaft couplings can be cracked by overtightening the setscrews. Allow the
Locktite to set 2 minutes before operating the switch.
6.11
Noisy or intermittent front panel control potentiometers [pots]
Cause: The grease, that is used to lubricate these pots, oxidizes and becomes gummy with age,
causes an intermittent connection between the rotating wiper-arm and the resistance-film in the
pot.
Fix: Stand the radio up on its back, on the original rear packing cushion. Pull-off the knobs of
the offending pots. Using a syringe and small-gauge needle, inject TCE degreaser down into the
clearance spaces next to the concentric shafts of these pots, rotating the shafts back and forth to
loosen the gummy grease. When the pot is no longer intermittent, inject GC Electronics Co.
"De-Ox-Id" . This material should be thinned with about 50% TCE to help fluid penetrate down
into the pot.
Note: TCE is carcinogenic and should be used with good ventilation.
6.12
On the AF-AVR Unit, the 4-pole relay contacts which switch the bias
to the finals may fail after extensive use.
This relay is neither cheap nor easy to replace. The failure is caused by th.00000 repeated
shorting to ground of a charged capacitor in the bias circuit by one set of the relay contacts
during T/R transition.
Fix: On the circuit diagram, find the leftmost set of contacts. The arm [movable contact] of this
set of contacts is grounded.
Fix: cut the trace from the arm to ground in 2 places about 5mm apart. Remove the foil between
the cuts. Solder a approx.100 Ohm, 0.25 W resistor across the gap. The resistor will limit the
peak discharge current during T/R-R/T switching to a value that will not burn the relay contacts.
12
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