[Elecraft] Line In problem ...

[Paul Christensen]

> I've simply tacked a jumper around L4 at the present time
> and will decide on a permanent fix later.  The more important
> question is why L4 would fail at all?

Joe,

Possibly a high DC offset from the external sound device or an accidentally 
high AC audio level at the KIO3's LINE IN jack.  If for example a sound card 
produced a high DC offset from it's LINE OUT jack that were present on the 
K3's LINE IN connector, then I could see where L4 could possibly fail.  At 
least as far as I can see in the K3 schematics, there's presently no 
coupling cap as part of the KIO3's LINE IN circuit

Since R13 (T1's series input R) limits the LINE IN current, it would take a 
substantial DC offset (or very high AC audio level) to cause L4 to fail.  If 
DC was the root-cause, then one possibility to avert an occurrence in the 
future is the placement of a 4.7uF coupling cap ahead of the KIO3's LINE IN 
jack -- or in the alternative, between the KIO3 LINE IN jack and T1.  With 
this cap value, the R13 series build-out R, together with the T1 primary 
would present a -3dB turnover point of ~ 30 Hz when driven from an external 
sound device with a low-Z output.

OTOH, perhaps L4 was on the ragged-edge of failing as a defective component 
anyway.  Anyone know a way to autopsy an SMT inductor? <g>

Paul,  W9AC