[Elecraft] troubleshooting # 4115

[Bud Rogers]

On Friday 02 April 2004 16:04, Don Wilhelm wrote:

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

Hi Don,

I have two problems that I think may be related.  One is a badly 
distorted transmit signal.  At first I thought it was oscillating.  I 
spent a lot of time around the BPF and LPF looking for cold joints or 
solder bridges.

Then I discovered that when I go into Spot to zero beat a received 
signal, the receive audio is also badly distorted.  So I've been 
looking around U8 and U10 on the control board.  Haven't found anything 
yet.

As I've poked and prodded things I've learned a little more about what's 
happening.  If I go into Tune, transmit is clean except it sometimes 
chirps right at the beginning.  If I use the key, transmit is 
distorted.  That probably means something, but I haven't figured out 
what yet.

> 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 think it may be outdated in the area you are working.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.

OK, that makes sense. 

> 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.

I have good sidetone.  I checked and U8 pin 4 is selected.  I continue 
to be amazed at this radio.  Somebody a lot smarter than me laid all 
this out.

> You should find the 2.5 Vrms at U8 pin 4 on your K2.  

I have a constant 5 VDC and 10.8 VAC at U8-4.  I'm thinking solder 
bridge, but I can't find it.

> 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.

That fits what I'm seeing.  Thanks for the tips, Don.

73,

-- 
Bud Rogers	<budr@netride.net>
KD5SZ		EM05vb		K2 #4115