And all 5-digit serial numbers Ive seen did not originally have the upgrades.And from what Ive seen, serial numbers from 0207xxx have the new board.
Icom Search Serial Numbers Ive SeenIts basically the same as the circuit described above, except it uses the smaller version of the MA77 diode (MA2S077). Two of these MA2S077 diodes are in series, in place of the large amber diode in the previous circuit. The other MA2S077 is used in place of the MA77 in the previous circuit. When I replace the FET, I solder a small heat-sink to its source tab. A 2AG-style fuse-clip fits perfectly by cutting off one of its legs, then soldering the remaining leg to the FET tab. R3 on the PA board should be 10 ohms, but some boards had a 4.7 ohm resistor instead. The excessive heat can eventually cause their solder connections to become intermittent, which causes fluctuations of the transmitter RF output. This affects all bands and all modes, and it is most noticeable by observing the ALC meter. The trick is to melt the solder on all three of an FETs strips at same time, while holding the FET firmly against the mounting plate, so it doesnt slide out of place. If youve re-soldered without the FET becoming loose, you didnt get it hot enough, and the joints will fail again. To get an idea of how the FETs are soldered, here are some photos. This may be more labor-intensive, but it eliminates the risk of damaging the traces of the DRV Board, as it requires considerable heat to unsolder its mounting pins. Removing the PA board only requires unsoldering the VHF SO-239 connector and two of the Varistor Boards. Here is spectrum analysis of an IC-746PRO with idling current set to 1.5 amps, compared to 0.5 amps. If this circuit fails, the transmitter will tend to oscillate intermittently. This is most noticeable on the higher HF bands (6, 10, or 12 meters). The symptoms are: unusually high current demand from the power supply, fluctuating RF output, andor erratic antenna-tuner operation. This test works because the attenuator interrupts the path of oscillation. The base voltage should be 0-volts RX, and 0.7-volts TX. The collector voltage should be 13.8-volts RX, and 0-volts TX.
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