[Elecraft] Ouch - An Update

[Mike Lewis]

So brought the K3 in to work this morning to our lab area where we have
static benches, blowers, wrist straps etc. and opened it up. Sure enough,
the T4 transformer was pretty crispy looking. My boss who is also an avid
ham (dream job setup :) ) then sprang into action. He removed the
transformer, counted the turns, removed the old wire, found some new magnet
wire of the proper gauge, rewound the toroid, and replaced both it and the
straight through portion (which had gotten pretty hot from the proximity to
the core.) Prior to stripping the burned turns off of T4 we looked at it
under a microscope and saw that the windings had burned open in one place,
effectively acting as a fuse of sorts. There didn't seem tpo be any other
parts, connectors, or board traces that looked to have been stressed. I
brought the radio home and hooked it up to a dummy load and a reasonably
accurate external wattmeter. It seems to be fine, both on receive and
transmit. 

 

I was hoping there was a built in SWR bridge cal procedure, but I didn't see
anything like that in the manual. The SWR values reported though seem to
match the LP-100A I am using externally pretty closely. I did try to follow
the Wattmeter calibration and ran into some confusion on the procedure as
written in the manual. I think I was able to puzzle it all out except for
one item - how do you change the config menu item from CONFIG:WTMR LP to
CONFIG:WTMR HP? It doesn't seem to change just by having the tune power
changed to 50 watts, so I am at a loss on how to change it.

 

So perhaps my K3 is now alright again, although I would appreciate any other
comments on other things to check or calibrate. And thanks to all on the
list who helped me out. After this the next project is to fuse the DC supply
cables to my DC blocks with some rationally small value of fast blow fuse :)

 

de Mike/KE0MF