I have a TRA931-X that I’m troubleshooting. Initially it was complete dead and it turned out that the fuse was bridged with a wire and the mode switch contacts were damaged.

I replaced both to find that there was a full short circuit on the DC input. This was caused by defective PA end transistors so I disconnected them and the short was gone.

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When I switched on the radio it immediately came in transmit mode and I think now I’m on to the initial problem.

When I disabled the TX/TX relay the radio went to RX mode and it is working fine on receive.

I suspected the PTT circuit because pin C on the audio was not grounded yet the line to the TX/RX relay was active (grounded) ?

When I did some checking around the circuit I found the CW key input was always grounded hence it triggered the TX mode.

According to the circuits in the manual I have (the manual that is also on the VMARS website) this should be a piece of cake because the key pin E on both audio plugs is directly connected to the key input connection on A41 of the MA930X board.

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Unfortunately not so on my version of the TRA931X. Pin E on audio 1 and audio 2 are not connected. The audio 2 pin E is connected to connection 11 of the switching and fixed level audio board but this is floating so is not the cause of the problem.

Pin E on audio 1 is grounded somewhere and I yet have to discover where it is connected to. For sure not to A41 key input of the MA930X board because they have a different colour.

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A further complication is that the switching and fixed level audio board in my radio is of a different (higher?) revision. It has 11 connection points and a different layout where the one in the manual has 10 connection points. The PCB number of my version is 713250 and the one in the manual is 713163.

The same is true for the ATU relay board. This is of a different layout and has only one relay instead of two on the one in the manual.

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Does someone know why the key line pin E on the audio plugs are no longer connected in parallel? Doe someone ever came across a newer version of the TRA931X schematics?

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Thanks,

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Nico – PA3ESA

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