[Elecraft] troubleshooting # 4115

[Don Wilhelm]

Bud,

First --- What problem are you attempting to troubleshoot?

I haven't looked at the troubleshooting manual in a while, but I think it
may be outdated in the area you are working.  Pin 25 of U6 was originally
the sidetone source, but when the KIO2 was developed, the sidetone was
changed to U8 pin 4.  The firmware has a selection for the sidetone source
to support K2s that have not been updated to the new sidetone source.

If you have no sidetone, enter the MENU, select ST L, then tap the DISPLAY
button - you will then be able to toggle between U6-25 and U8-4 with the VFO
or band+/band- buttons.  Select U8-4 for newer K2s.

You should find the 2.5 Vrms at U8 pin 4 on your K2.  Without the KIO2 or
KPA100 installed, U6 pin 25 will likely be at 5 Vdc and may have some
'funny' undefined AC signal as well - that is the source for the RS-232
Transmit data signal.

73,
Don W3FPR

----- Original Message ----- 


> I'm working my way through the troubleshooting section of the manual.
> Page 13, right column items 5 and 6 refer to AC voltage on pin 25 of U6
> on the control board.  Item 5 identifies pin 25 as the source of the
> sidetone signal.  Item 6 refers to an expected 2.5 Vrms.
>
> I measured 10.7 VAC and 5 VDC on pin 25, in both tune and receive.  The
> voltage chart calls for 0 VDC in receive.  Looking at the schematic,
> pin 25 of U6 is labelled TXD.  It doesn't appear to go anywhere except
> to pin 1 of P4, with C43 bypassing to ground.
>
> What am I missing?