[Elecraft] Builder Alert #19: current metering (C42 and C44)

[Wayne Burdick]

APPLICABILITY

Revision A and XC K2s:   ALL
Revision B K2s:          Serial Numbers 3000-3077


BACKGROUND

This builder alert replaces alert #17 -- PLEASE READ.

Builder alert #17 had recommended the addition of C44 (0.1 uF) to the Control
board on older K2s. This capacitor is also present on the revision B K2. Based
on further testing and field reports, we have determined that C44 should NOT be
used. In some cases it can cause current-measurement inaccuracies of as much as
25% at transmit currents of 2 amps or higher.

Alert #17 also mentioned increasing the value of C42 to 0.1 uF. This change is
still required on older K2s. Revision B K2s already have the correct value of C42.


MODIFICATION INSTRUCTIONS

If your K2 is revision B (s/n 3000-3077 only):

  - Remove C44 on the Control board. NOTE: This is specified on the errata
    sheet for revision B K2s starting with serial number 3078.


If your K2 is revision A or XC:

  - If you added C44 previously (alert #17), REMOVE IT.

  - If you did not increase C42 (alert #17), do so now.
    Use an 0.1 uF or larger ceramic or monolithic capacitor (not electrolytic). 
    If you don't have any suitable capacitors, send a request to
parts@elecraft.com 
    and we'll send you an 0.1-uF cap at no charge.

    NOTE: If you built a KPA100, you have already made the change to C42.