40M Disappears After One Hour - Repair advice from KJ4WS

The 40 Meter Crystal is Y4. Sorry but I didn't go deep enough to get the frequency. You could have a bad crystal but here is what I have been running into lately.
1. An Omni 6 opt 3 that would not do a proper CW transmit offset
2. Another Omni 6 Plus which 30 Meters would fall out after a few minutes of operation
3. Grady/AD4GB, had an Omni 6 which had no 20 Meters.
4. My Paragon, a bit different because this was a problem with the Low Pass Filter Board.

And the list goes on and on where missing bands have been concerned. Each of these problems was a PIN Diode. In your case it is D12 on the OSC-Low Mixer Board. If you look at page 6-14 of the Manual, or page 52 of 132 of the .PDF on your computer, you will see Connector 82 ( osc-low mixer board). The band switching is done by applying a positive voltage to the proper diode to activate the proper crystal.

Sorry but I don't have an Omni 5 for reference but if you place the rig on 160 meters, one end of the connector will have a positive voltage. Switching to 80 meters the second pin in will be switched on and the voltage on the end pin will go away. And on 40 meters it will be the third pin in on this connector. I am sorry to have to drag this out this way but I can only tell you to start at 160 for the pin on one end. And then 80 will be the second one over and 40 the third pin in. So when you switch to 40 meters just make sure that the switching voltage is there and stable. If that voltage is there, don't check … REPLACE … D12. D12 is the PIN switching diode for the 40 meter crystal. These switching diodes have been a very common problem/repair for me lately. Looking at the board and where the first crystal is closest to the edge of the board, it will be the third crystal and diode over. There is an R7 680 ohm resistor across the crystal but, we have never had a problem with one of these. Most any Small Signal Silicon Diode will work in this circuit. Looking at the parts list for D12 or a call to Ten Tec should get you a diode or suitable substitute.

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