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| Troubleshooting Guides: IC-471A/H
- Trimmer Capacitor Alignment |
| 1.) |
Replace all plastic
trimmer capacitors in PLL/VCO and RF/YGR circuits with ceramic
types: 6 pf, 10 pf, and 20 pf; as called for in the service manual. |
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| 2.) |
Monitor J4 test point
with a spectrum analyzer for a signal in the 265 MHz range. Adjust
C16, C18, C25, C29, C35, and C38 for peak signal on analyzer. (Don't
use an IFR 1200 service monitor; the signal will overload its
analyzer.) Output level at J4 should be 0 db or greater. Switch
between 430 and 440 MHz on the radio and fine tune the previously
listed caps for no more than a 2 db variance between the two
signals. |
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| 3.) |
Monitor PLL output with
a spectrum analyzer (not IFR1200) and adjust C58, C61, C70, C76, and
C79 for peak signal. This must be a minimum of 0 db. Next, fine tune
for no more than a 2 db variance between 430 and 449 MHz in 1 MHz
steps. |
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| 4.) |
Align 10.25 MHz
oscillator on PLL unit. |
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| 5.) |
Align VCO as per the
service manual alignment procedure. |
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| 6.) |
Set the 430 band
frequency and 440 band frequency as per the service manual. |
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| 7.) |
Realign RF/YGR unit for
maximum performance. Alignment at 440 MHz will usually yield good
performance from 430 to 449.995 MHz. |
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