Hi Per-Tore, Can you identify which transistor (or other device) on the LPA module is getting hot in transmit mode?
The drain terminals of MOSFET PA transistors Q4 and Q5 receive +12V regardless of TX or RX mode, but the gate bias voltages are applied only in TX mode. Unless there's a problem with the bias regulator circuit (U1), the RF amplifier chain on the LPA module should not be getting that warm. It is also possible that one of the RF power transistors may be getting hot because it is no longer making good thermal contact with the bottom cover panel - it would be good to check the tightness of the three screws holding those transistors against the bottom panel. Is it possible for you to carefully extract the LPA module from the main RF board? That requires removal of the rear panel of the bottom cover, and you may need new thermal pads for the RF transistors if those pads are damaged by removal of the cover panel. If you can remove the LPA module, you might try RX mode ONLY with the Power control set to 0 (to ensure that the KPA3 PA is bypassed by its relay K1) and see if your receive sensitivity is restored. The output side of the LPA module is nominally connected only in TX mode to the antenna path via diode D1 on the LPA module, and if the D1 switch is operating properly one would not expect the high attenuation of signals in RX mode. The output of the LPA module is also connected to the input of the 100 W PA module at the same point on the T/R switch circuit, but that module is bypassed by relay K1 on the KPAIO3 board. I'm not yet sure how the overheating of a device on the LPA board is connected to the loss of RX sensitivity. If the diode switch D1 on the LPA module has failed shorted (unlikely), then it would leave the output circuitry of the LPA module bridged across the antenna signal path in RX mode. Keep us posted on what you learn! 73, Mike, K8CN -- Sent from: http://elecraft.365791.n2.nabble.com/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
