KN3U

Dick explained exactly what you need to do. To answer the second part of the question -- a very good question, by the way -- RF current is concentrated near the surface of the conductor. For aluminum conductors at HF frequencies, most of the current is confined to the outer 100 µm (micrometers) of the conductor. The higher the frequency, the more shallow the skin depth, so at 30 MHz (10 m) the effective skin depth is about 15 µm. That's a surprisingly tiny fraction of the tubing cross-section, but then electrons are pretty small, so a lot of them fit in that tiny amount of area. So, the part of the outer antenna element that is telescoped inside the larger-diameter tubing provides mechanical strength (and an easy way to tune the antenna to resonance) without having any effect on electrical performance. The current literally follows the skin of the antenna element over its entire length. The tiny jump where the tubing changes diameter has negligible effect at HF frequencies. You can google "skin effect" for more information.

These symptoms that you are describing relate to functions implemented in software, not hardware. All the front panel switches and rotary encoders are read as DC voltages by an analog-to-digital converter (ADC) built into the the microprocessor. See page 4 of the front panel schematic. A voltage divider string connected between 5 VDC and ground applies a different DC voltage to each string of switches. The voltage divider has seven "taps" ranging from 1.5 V to 4.5 V in half-volt increments. There are eight inputs to the ADC. The microprocessor constantly scans the ADC inputs and knows which switch is being pressed by the voltage level and which ADC input it appears on. For example, the tuning rate switch is connected between TAP 6 on the voltage divider and ADC input 1. TAP 6 is 2 VDC. So when the microprocessor reads 2 VDC on ADC input 1, it knows the rate switch is pressed. (I'm simplifying things somewhat, but that's the general idea.) The bottom line is that, if the 5-volt regulator is malfunctioning and putting out a voltage that is different from 5 VDC, the microprocessor will be confused as to which switch is being pressed. So it is worth checking that supply voltage. The 5-volt regulator on the front panel PCB is U10, a 78M05 chip. Rick, C102 on the front panel board filters the contrast voltage applied to the LCD display, so that's not likely to be the culprit here. I'm curious, though. It sounds like you have found a source of troubleshooting information. If so, I'd like to know about it. I'm just working from the K3S schematic diagrams published by Elecraft. Ak KN3U

Q2 on the RF board is a P-channel MOSFET functioning as a power switch. You can probe it in place. The source (pins 1, 2, 3) are connected to the 12 VDC main power input through a polyswitch (resettable fuse) and a Schottky diode. Verify that you have 12 V on Pins 1-3. Pin 4 is the gate of Q2. When it is grounded, the MOSFET turns on and 12 V should appear on the drain (pin 5-8). The signal that grounds the gate of Q2 comes from the front panel PCB. It might be hard to probe Pin 4 directly, but you can put your probe on any of the components connected to pin 4 -- R76, R77, or C226. If Pin 4 doesn't go to ground when you turn on the radio, you'll have to go back further to the front panel PCB. On that board, there is a signal called /PWRON that is driven by the Microprocessor. It's unclear from the schematic exactly how that works, but here's what I think might be happening. It appears that the Power Switch is a momentary pushbutton. When you press the power switch, that turns on Q3, which grounds the /PWRON line (and goes to the gate of Q2 on the RF board. That applies power to the radio, including the microprocessor. The microprocessor then asserts the POWERHOLDON signal, which turns on Q2 on the front panel PCB. That keeps the /PWRON line grounded when you release the power button. A second push of the power switch sends a different signal to the microprocessor to shut the radio down. So, the bottom line is this: In order for the radio to turn on and stay on, Q2, Q3, and the microprocessor on the front panel PCB all have to work, as well as Q2 on the RF board. Looking at the gate of Q2 on the RF board, press and hold the power switch and see if the gate goes to ground. If so, power will come on on the RF board. Then see if the gate remains grounded when you release the power switch. My guess, since you have been able to communicate with the microprocessor, is that the circuitry on the front panel PCB is ok and your issue is a bad Q2 on the RF board.

I understand. The factory reset does install a default configuration file, so if the reset is successful, the radio will be fully functional. You can always install a custom config file later, if one is found. There is plenty of advice to be found on the web regarding ways to customize the configuration for different pursuits such as DXing, contesting, or VHF/UHF activities. Fred Cady, K37X, wrote a book on the K3 with more detail than the manual, including advice on how to set up the radio for different pursuits. Elecraft sells the book, and I think Amazon carries it as well. Talk to you soon, Al KN3U

One other thought -- you might try reloading the firmware using the K3 Utility program. Chances are that you have already tried this. First, try a factory reset. In the manual (page72), it is called Parameter Initialization. Then see if you can connect to the radio using the K3 utility. If so, you can try sending all the firmware to the radio.

The choice of whether to use a repeater or simplex should be based on the situation. It is not a “one size fits all” situation. It is all about size. Simplex is fine for a 5k run in flat terrain with no obstructions. We used to support a 5k run in which half the race course was on level ground and the other half was down a steep hill. We used 2 m simplex on one half of the course and 70 cm simplex on the other, and used a crossband repeater sited at the top of the hill (TM-D710) to link those two frequencies. That worked beautifully — everyone on the flat half of the course could hear each other, and everyone on the downhill side of the course was also within simplex range. The crossband repeater linked these two cohorts into one. That’s a special case, but it might apply to other events. The problem with the event we supported a few weeks ago is that, between the hilly terrain and buildings, simplex doesn’t work well. And their are no nearby repeaters that provide full coverage of the area. A portable full-duplex (conventional) repeater is what makes the most sense in that situation, and that’s what we need to do next year. Crossband repeaters work very well to link two simplex frequencies. They do not work so well when trying to access a distant repeater. For example, consider a situation where you need to set up a station in a hospital or shelter where it is not practical to have an external antenna and you need to reach a distant 2 m repeater. You might be a ale to set up a mobile rig as a crossband repeater with Band 1 of the mobile rig set to reach the distant repeater and Band 2 set on a 70 cm simplex frequency. You access the crossband repeater from inside the building via 70 cm. The problem is that most crossband repeaters are half-duplex. It won’t retransmit your 70 cm signal until the carrier of the 2 m repeater drops. And if there is a lot of traffic on the repeater, the carrier might not drop for an extended period. You are effectively prevented from breaking in to the conversation.

Gil, Look here: C:\Users\<your username>\AppData\Roaming\Elecraft\K3 Configuration\SN06398.20220731T143229.K3Config The filename has the serial number, period, date (YYYYMMDD), the letter T, and the time (HHMMSS) the file was created. Or just search for "*.K3config". Al KN3U

Gil, There is an Elecraft forum at elecraft@groups.io. I am not a frequent visitor, but the forum has a number of very knowledgeable members. It is highly likely that you will find recommendations for repair services there, and probably also troubleshooting tips. It seems likely that the radio experienced a voltage surge. Diode D28 is a solid-state transient voltage suppressor (TVS). It is similar to a Zener diode, but designed to absorb moderately high-energy surges. it presents a low resistance to voltage exceeding a specified threshold, clamping the voltage seen by the downstream circuitry. If the overvoltage condition is extreme, the current flowing through the TVS will blow the radio's main fuse. WHen a TVS fails, it usually fails in a short-circuit condition, sacrificing itself to protect the downstream circuitry. That particular part number, BZW50-15, starts conducting when the incoming voltage reaches between 18 and 20 VDC. Because the TVS has a small but measurable resistance, if the surge current is large enough -- for example, due to a nearby lightning strike -- the clamping voltage seen by the downstream circuitry may rise to as much as 30 or 40 V for a brief instant before the fuse blows. That's enough to cause downstream damage, and you might have multiple failures. Your symptoms make it sound like the power supply voltage coming into the radio did experience a voltage surge. If you were not experiencing lightning conditions during Field Day, I would be very suspicious of your power supply. In many power supply designs, the failure of a series pass transistor can apply a large unregulated DC voltage to any connected equipment. In addition, if the power supply has a voltage adjustment, the potentiometer that controls the output voltage may become intermittent with age and result in a transient overvoltage condition. So this is something to look at, lest you damage another radio. Better-quality analog power supplies have an independent protection circuit called a crowbar circuit to prevent an overvoltage condition. Switching power supplies may employ a variety of overvoltage protection schemes having varying effectiveness, or none at all. Not all power supplies sold in the ham radio market -- including some major brands -- have overvoltage protection. Good luck. Al KN3U