K1 Problem Diagnostics

It’s been quite long since I last looked at the K1. To tell you the truth, I’ve been very busy with work and gpredict. But now it’s time to fix the K1 and get it on the air before the summer is over.

Last time I have located the failure to somewhere around U5, but I didn’t really know which part, or board for that matter. Therefore, I have removed the front panel board and measured again. I get the same result with the front panel board removed. The input pin of U5 seems shorted and the RF board draws max power or, more precisely, it shorts the power supply.

I have cut the input leg of U5 but it made no difference… Still the same behavior :-L

There are two more places where the 12V is used, both places related to the transmitter. The first possibility is the Buffer following the TX mixer. This one can be isolated by cutting the jumpers that has been mounted instead of RFC8. The second place is the PA itself and this time it may well be related to a shorted D19. I have cut one leg of D19 and it fixed the problem! Hurray!

I have removed D19, resoldered U5 and the K1 is alive again. I will order a new D19 from Elecraft and… well… a tuner board as well… Come on… I want to save postage…