Hi George, Your test confirmed that the low-power amp (K3 LPA) survives. To clarify, do you have the K3 or K3s?
The original 100 watt PA (KPA3) used RF BJTs as the finals, whereas the KPA3A used RF MOSFETs (LDMOS). Apart from failure of one of the PA final transistors, the loss of TX output power when the 100 watt amp is switched in can be due to failure in the PIN diode T/R switch around the 100 watt PA. The fact that you can generate 12 watts indicates that the '100 watt module bypass' path through the PIN diode switch is OK. Failure of the PIN diode switches connecting the LPA to the 100 watt PA can arise from failure not only in the PIN diodes themselves, but also from the bias circuitry that switches the diode states. A recent post with a similar problem revealed the fault to be in one of the RF chokes (the red toroids on the 100 watt PA board) that feed DC to the PIN diode switches. The problem was a broken wire on one RF choke. I suggest opening the top cover, do a visual inspection of the top of the 100 watt PA module, then remove the 100 watt PA module to inspect the underside. Barring any obvious sign of burned components or board traces, the next step would be to check the PA transistors, but the actual test depends on whether your K3 has the older BJT finals or the more recent MOSFET finals. Let us know what you find....., and 73, Mike, K8CN ______________________________________________________________ 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
