[Elecraft] K3 Erratic SSB Power Output

[Roger Crofts]

Jack, G8DX, wrote that his K3 has erratic output.

I had the same fault on my kit-built K3 (ser # 6906)
In fact my problem was worse, because at times I had no output and, occasionally, the K3 (set to 20w) would drive my Metron Linear Amp with 110w causing the breaker to trip.
I followed the instructions from Elecraft support, and the problem improved, but it never went away completely.
After 6 months the problem got much worse until output power failed completely. This was a blessing, because it was then
easy to trace the fault. The fault was on the LPA board. Diode D1 was not soldered at both ends. Diode D1 is directly in the transmit path. It is a surface-mount device, and is not visible until the 100watt amplifier module is removed. Under the microscope, the contacts of this diode appeared slightly tarnished or dull.
In a normal manufacturing process, each circuit board is fitted with a solder mask, and solder paste is wiped across the mask. This deposits exactly the right amount of solder paste on each solder pad. Then a Pick-and-Place machine places the components on the pads. Then, the loaded boards move slowly on a conveyor belt through a re-flow oven. All the connections are made perfectly.
This process can occasionally go wrong. Because the contacts on D1 were slightly tarnished, the solder did not flow properly. The problem did not show up during testing at the factory because the contact was still touching the pad. Components come in batches, and if one diode has this problem, there may be other K3s out there with the same problem. If your K3 is showing this symptom, it might be a good idea to take a good look at the connections of D1 on the LPA board. After hand soldering the connections on D1, the output power from my K3 is now rock solid.

73, Roger, VK4YB