Hi KA6BPV,?
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I posted a video a few months ago in response to a Youtube viewer who had no TX on 70cms. The 2m VHF and 70cms UHF TX paths are very closely related, so this 70cms video will help you understand the potential areas to look at for no TX on 2m. Here is my channel video: ?
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In this video, I review the schematic from the TX predrivers, PA finals and into the RF filtering to the antenna. Alas, most of the components will sit on the underside of the RF filter board, so you would need to pull the board out. And when out of the rig, there is no easy way to test the radio, so you will have to revert to basic diode testing of the diodes or transistors that could be affected, but this is straightforward with a multimeter diode test function: test the diode/transistor junctions wiht leads one way, then reverse the leads and retest. You can expect 0.7V(ish) in the conducting direction and 'OL' in the other. Anything else and it makes one suspect the diode/transistor is faulty.
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Schematics are found on the internet - I use ? ?For an early FT817 (early LOT numbers), go to page 71 for the relevant schematic page, and p. 73/74 for the physical board layout drawings. There were some very modest changes in components in later versions (changes from resistors to inductors in the RX path for example), nothing significant in 2m troubleshooting. Look here to identify your LOT number as the schematics (different pages in the pdf above) to change:
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Before pulling the board out: confirm the rig RX on 2m with no issues - this helps narrow the issue to TX related control voltages, and RF TX path switching via relays. If there also no RX on 2m, the issue could also then be in the LPF and HPF circuits with an open or short/low impedance path to ground.
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Good luck and let us know how it goes.
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73 de Matt, M0NJX
Westerham, Kent, England.
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