[Elecraft] K2 Builder Alert: R19 on RF board wrong value

[Wayne Burdick]

K2 BUILDER ALERT #18: R19 on RF board is the wrong value


Applicability

This builder alert applies to:

  - new K2s with serial numbers from 3000-3055
  
  - older K2s that have been updated with the BFO/PLL mod kit, 
    if a value of 220 ohms was used for R19


Background

Resistor R19, on the RF board, was recently added to the design. It extends the
tuning range of the PLL reference oscillator to make it easier to cover the
required range with a single crystal. 

The value of R19 should have been between 1.8 and 3.3 k, but 220 ohms was
supplied. This smaller value can result in VFO tuning non-linearities of as much
as 70 Hz at certain points in the VFO tuning range. We strongly recommend
replacing R19 with a larger value as described below.


Change Required

1. Replace R19 with an ordinary carbon-composition or carbon-film resistor
between 1.8 k and 3.3 k (any power rating, any tolerance). On the Revision B RF
board, R19 is located on the bottom of the board near the PLL reference
oscillator crystals. There is no R19 on earlier K2 RF boards. But if you removed
one PLL reference oscillator crystal as part of a temperature-stability mod, you
may have added R19 to the board (soldered between pins 7 and 8 of RP2).

NOTE: The resistor's power rating can be anything from 1/10th watt or higher,
but use a resistor that will fit on the bottom of the RF board without
interfering with the bottom cover. Do not use a wire-wound resistor. If you do
not have a suitable resistor, you may request one from Elecraft by sending
e-mail to parts@elecraft.com. Ask for Elecraft part number E500005 (2.7 k, 1/4 watt).

2. Re-run CAL PLL. If you have revision 2.XX K2 firmware, CAL PLL is to be done
only on 40 meters. If you have 1.XX firmware, CAL PLL must be run on all bands.
In either case, refer to your K2 manual or the application note you used when
adding R19 to the board.

3. Note this change on the K2 schematic (RF board, sheet 1).