AMX TXC16 Plus Specifications download pdf (Page 155)

SG-2000 MANUAL 148

The SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA

23.1.4 11.94 MHz Reference Oscillator Test

The oscillator will drift for the first 10 minutes after power is applied while the

surrounding oven warms up. Check for ~ 1.6 volts on R619 when the power is

first turned on. (In the event of failure, refer to the crystal oscillator section of

the schematic.)

Check TP604 (or pin 14 of IC610 on older boards) for 11.94 MHz, 6 ±.5 Vpp.

Adjust capacitors C639 (fine) and C640 (coarse) for 11.94 MHz ± 2 Hz on the

frequency counter. Note: do not adjust C639 and C640 if the radio has been on

for less than 15 minutes.

Verify that the oscillator will work properly with SW501 oven switch in both

positions.

23.1.5 VCO Checks

VCO 4, 10.7 Oscillator

Set radio in USB and A3J mode. Check for 4.8 VDC to 5.1 VDC on L416.

Note that the 10.7 oscillator is disabled and there is no voltage on L416 only if

the radio is in receiving A3H mode (in all other modes, Q409 will be biased).

Attach frequency counter to TP403 and the voltmeter to TP603. Adjust C447

for 5 volts ± 0.2 volts on the voltmeter. Frequency counter should read 10.7

MHz (USB).

Attach oscilloscope to TP403 Adjust T404 for the maximum level,

approximately 1.4 Vpp volts on the oscilloscope.

In the event of failure, refer to the VCO troubleshooting section.

VCO 2, 72 - 76 MHz Oscillator Check

Set radio frequency to 29.9999 MHz.

Attach scope to TP402, it should read 2 ±.5 Vpp.

Attach voltmeter to TP602 and frequency counter to TP402, use a X1 probe on

the frequency counter.

Adjust L410 for 5 ±0.2 VDC.

Frequency on TP402 should be 75.60 MHz.

In the event of failure, see the VCO troubleshooting section.

Secure L410 on PCB with a few drops of polystyrene Q-dope.

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AMX TXC16 Plus Specifications Page 155