ELECRAFT K2 BUILDER ALERT #22a
KPA100 Cap Kit Upgrade
1 Aug, 2005



APPLICABILITY
This builder alert applies to ALL KPA100s shipped until July 20, 2005.   If your KPA100 was shipped after then, or if it puts out 100W on 20M and 17M without drawing much more than 20 amps at 13.8V, it does NOT need this upgrade.


BACKGROUND
Several builders have reported difficulty in reaching full power on the 20 and 17 meter bands. In other cases, while full power was reached, the current drawn by the K2 was abnormally high when operating in the 20 and 17 meter bands. The high current draw is an indication of lower than normal gain in the KPA100.

It was found that the manufacturer of the resistors used in R19 and R20 changed the internal design, resulting in resistors that became inductive at certain frequencies. It was found that replacing R19 and R20 with resistors from another source returned the KPA100 to normal operation. The improved resistors will assure that this problem will not reoccur. This kit provides the parts needed to install the upgrade and restore your KPA100 to normal operation.

Parts List

2ea  1.6 ohm resistor, 2 watt E500177

Modification Procedure.

  1. Turn off the K2, turn off the power supply, and disconnect all rear-panel cables.

  2. Remove the six screws retaining the KPA100 module and lift it out carefully, disconnecting all internal cables.

  3. Remove the seven zinc-plated (bright) screws holding the KPA100 shield to the PC board. Do NOT remove the three black screws that hold the grounding clips to the shield (applies if you have the newer shield).

  4. Locate resistors R19 and R20 on the top (or component) side of the board, found near power transistors Q1 and Q2.

  5. Using heavy duty wire cutters, cut the legs of the resistors as close to the body of each resistor as possible and discard the resistor parts.

  6. Using your soldering iron, heat the leads of the clipped resistors at the solder pads in the pc board and use small pliers to pull them off the top of the board.

  7. Use solder wick to clear the holes from any remaining solder.

  8. Locate the two new 1.6 ohm resistors that came with this kit.

  9. Precut and bend the leads for the new resistors so they will just protrude out the bottom of the board (about three eighths inch long).

  10. Insert the resistors from the top (or component) side of the board into the holes for R19 and R20 and solder the leads from the top of the board.

  11. Reinstall the shield. Tighten the hardware to ensure good contact at both ends of the ground strap.

  12. Turn the KPA100 assembly over carefully and install it in the K2, re-connecting all internal cables.

  13. Check the PA transistor hardware, tightening the screws as described in your assembly manual. This is VERY IMPORTANT, as loose hardware can lead to damaged transistors.

  14. While putting the side-panel screws back in, please be very careful not to over tighten them as this will strip the screws!

  15. Make sure the left and right spring clips are touching the side panels, and that none of the interconnecting cables are pinched.

This completes the KPA100 resistor upgrade.