11
Installation time for this procedure is 1/2 hour or less.
6.7 Intermittent ALC on transmit
6.7.1 Problem 1: Intermittent ALC indication [TX] on only one band
This indicates that the trouble is different than was the case in Problem 2 {which would be the
same on all bands}. The bandswitch is usually the culprit. This occurs most often on the 7 MHz
band-switch position, on the two, rear-most bandswitch sections in the RF Unit.
Cause:
The bandswitch (also) has dissimilar-metal crimp-connections that turn into semi-
insulators due to electrolysis. This takes place between the bandswitch's riveted-on,, tin-plated,
stationary contacts and the copper-foil on the printed circuit board [PCB]. Fix:
Apply a small
amount of conductive-paint where the stationary switch contact touches the copper-foil on the
PCB. The conductive-paint will be drawn, by capillary-action, into the problem area where the
two, dissimilar-metals touch each other.
6.7.2 Problem 2: Intermittent ALC on transmit
Cause: As in problem 1, this problem is usually caused by an intermittent crimp-connection on
the pins at the ends of the coax cable that brings the transmitter intermediate-frequency ["TIF"]
signal from the IF Unit to the RF Unit. The ends of the TIF coax cable can be found in the same
connectors that were discussed above, in Problem 1.
The fix
is the same: Make good electrical connections at the crimps on the connectors' pins.
6.8 Lack of crispness in receive audio
Cause: The intermediate-frequency bypass capacitors, C62/C63, at the audio output of the
product-detector, are so large that they noticeably attenuate the treble audio frequencies.
Fix:
Reduce the value of these capacitors and reduce the terminating resistance, R78, across the
output capacitor, C63, to reduce the treble attenuation. R78 is changed from 47 KOhm to
approx. 3.3 KOhm - 4.7 KOhm. C62 and C63 are changed from 0.022 µF to 0.0075 µF -
0.01 µF. {the factory value varies depends on the radio's S/N} These components are on the IF
Unit, about 4cm in front of the left-rear corner. Note: After this change is made, the full range of
audio frequencies will be present in the background/"sky" noise. It is beneficial to compensate
for this by turning down the RF Gain control until the sky noise decreases to a comfortable
level. [This is the main reason to have an RF gain control.]
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