K2 4907 - Still no audio

[Zac Brown-2]

Fellow builders,

I've been working on building my K2 as time permits since may of 2005.
I was hoping to have it completed by now, but got stuck on a problem and
haven't had the time to really delve into it until recently.

Back in 2005, I posted a question to the group - the topic was "No Audio
Except during Menu".  I'm still having this problem.

I've been exchanging emails with Gary, and feel like I'm getting close
to finding the problem.

Here's a summary of things that I've checked so far:

R12 looks fine, squelch is turned off, the 18C452 MCU looks fine
(measuring all pins results in expected values, have already pulled the
MCU and verified that all pins are straight, etc ... ), visual
inspection of solder points revealed no solder bridges or cold solder
joints, all resistance checks are passing.  Nothing aside from the base
  K2 kit is installed.

D9, however, is exhibiting some strange behavior.

When I'm in normal receive mode, D9's cathode is measuring about 1.9
VDC.  Gary tells me that it should be close to 0 VDC in receive mode,
and that if it goes much above 1 to 2 VDC (in receive) that the MCU will
turn off the 8R line, resulting in what appears to be a dead receiver.

When I go into the menu, as soon as I scroll past the ATU entry
(I have no ATU installed btw, just the base K2 kit), D9's cathode drops
to about 0 VDC, and I hear audio at that point.  It stays like that as
long as I remain in the menu.  As soon as I exit the menu, D9's cathode
goes back to about 1.9 VDC and I hear no audio.

If I put a piece of wire across D9's connection points (bypassing D9),
then I hear audio all the time.

I feel like I'm getting close to finding the problem.  Any ideas what
could be causing this?  It's probably something that I did wrong while
building the radio, but I'm not sure where to look at this point.

Thanks,

Zac Brown
KD5IEF
K2# 4907
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[Don Wilhelm-3]

Zac,

If D9 has DC Voltage on the cathode, either there is RF on your antenna or
you have something wired wrong.  Does the voltage at the cathode of D9
remain if you disconnect the antenna?  Do you have any DC voltage on the
anode of D9?  That should be zero volts.

Are you certain the K2 is not going into transmit?  What is the voltage at
the anodes of D6 and D7.  If your K2 is in transmit state, there should be
about 8 volts at the anode of D7 and the anode of D6 should be zero.  In
receive state, the opposite should be true - 8 volts on the anode of D6 and
zero on the anode of D7.

You could temporarily remove R66 to see if the voltage is being produced by
RF on the antenna side or if there is something wrong with the wiring on the
VRFDET signal line inside the K2.

With R66 removed (and the jumper removed from D9), what is the voltage on
the Anode and cathode of D9 - it should be zero in receive at both points.

73,
Don W3FPR

> -----Original Message-----
>
> I've been working on building my K2 as time permits since may of 2005.
> I was hoping to have it completed by now, but got stuck on a problem and
> haven't had the time to really delve into it until recently.
>
> Back in 2005, I posted a question to the group - the topic was "No Audio
> Except during Menu".  I'm still having this problem.
>
> I've been exchanging emails with Gary, and feel like I'm getting close
> to finding the problem.
>
> Here's a summary of things that I've checked so far:
>
> R12 looks fine, squelch is turned off, the 18C452 MCU looks fine
> (measuring all pins results in expected values, have already pulled the
> MCU and verified that all pins are straight, etc ... ), visual
> inspection of solder points revealed no solder bridges or cold solder
> joints, all resistance checks are passing.  Nothing aside from the base
>   K2 kit is installed.
>
> D9, however, is exhibiting some strange behavior.
>
> When I'm in normal receive mode, D9's cathode is measuring about 1.9
> VDC.  Gary tells me that it should be close to 0 VDC in receive mode,
> and that if it goes much above 1 to 2 VDC (in receive) that the MCU will
> turn off the 8R line, resulting in what appears to be a dead receiver.
>
> When I go into the menu, as soon as I scroll past the ATU entry
> (I have no ATU installed btw, just the base K2 kit), D9's cathode drops
> to about 0 VDC, and I hear audio at that point.  It stays like that as
> long as I remain in the menu.  As soon as I exit the menu, D9's cathode
> goes back to about 1.9 VDC and I hear no audio.
>
> If I put a piece of wire across D9's connection points (bypassing D9),
> then I hear audio all the time.
>
> I feel like I'm getting close to finding the problem.  Any ideas what
> could be causing this?  It's probably something that I did wrong while
> building the radio, but I'm not sure where to look at this point.
>
> Thanks,
>
> Zac Brown
> KD5IEF
> K2# 4907
>

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