Hi Gary, The K3 computes forward and reflected power from samples taken in the SWR bridge circuit. A Tif X Gain calibration could fail because the forward power reading is incorrect due to a failure in that portion of the SWR bridge circuit.
Do you have the KAT3 ATU in your K3? If so, be sure that you select BYPASS using the ATU TUNE button on the front panel. The K3 Utility will do this automatically on each band if you run a TX Gain Calibration via the Utility. Unfortunately, with the exception of two 51 ohm bridge termination resistors on the top side of the RF board, the remaining bridge components are on the underside of that board. You can access them by removing the rear bottom cover, but DO NOT key the transmitter while the cover is off because it will kill the driver transistors in the Low Power Amp assembly. I would check diodes D36 and D37 on the RF board first, which form the RF detectors for the forward and reverse power metering circuits, respectively. Those diodes are DC forward biased and should show a forward voltage drop of perhaps 0.3-0.4 V when sitting idle (transmitter NOT keyed). If those diodes are OK, then it gets more tricky to troubleshoot the SWR bridge without access to the bottom side of the RF board (DO put the rear bottom cover back in place before any further testing proceeds!). This is where Keith, WE6R, the K3/K4 super-tech at Elecraft, should be consulted about other possible failures in the SWR bridge circuit. There may be vias accessible on the top side of the RF board that would enable you to measure the VFWD and VREFL voltages from U16 (op amp unity gain buffers), but I don't know that level of detail without opening up my K3 for careful inspection. 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
