No SSB Output

[Treat Hull]

I recently completed K2 Serial No. 5711 and I can testify from first hand
experience that assembly is fun, but that trouble shooting is where you
really learn how it works. I've resolved a few initial problems on my own,
but now I have a persistent problem with SSB which I have been unable to
solve by myself.

 

The symptom is as follows: Monitoring the K2 output with my other radio, an
Icom 706, I have a good signal on CW, but no output on SSB, either voice or
PSK31.

 

For trouble shooting, I first went over all the boards, with particular
attention to the torroid leads on T1 and T2, plus the diodes, per an earlier
posting by Wayne. When everything checked out there, I followed the
procedure recommended in Don Wilhelm's posting of 11 Jun 2006.

 

First, I used my scope and verified that I had a good good BFO signal to U5
pin 6.
 
Then I set up my audio signal generator for about 50 mV peak-to-peak at
about 1,000 Hz and fed it into the mike connector pins 1 and 7 (which I had
wired for a Radio Shack mike with AF to Pin 1, PTT to Pin 2, and 7 and 8 to
ground).
 
When I used my scope to trace the AF signal, I started with the K2 powered
down. I found that I had a strong AF signal all the way to Pin 4 of U3.
However, when I powered up the K2, I lost all AF at Pin 4 of U3. Working
backwards, I found that I had AF as far as the junction of C32 and C33, but
no further. It's as though Pin 4 of U3 is going to ground when the unit
powers up. It behaves the same way with PTT open or closed.
 
Can any shed some light on possible causes that I might investigate further?
 
Thanks in advance,
 
Treat Hull
VA3IMO

 

 

 

 

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[Marshall Jose]

Treat,

I assume your scope was AC-coupled when you measured U3-4; some scopes
misbehave when DC-coupled.

I looked at the PC layout and wondered if a solder bridge to a nearby
pad might cause the symptoms, but it doesn't look like it. The trace
running from U3-4 goes around a bit, but it doesn't pass by any node
whose impedance drops when the circuit is energized.

You would do well to verify the DC voltages on U3 given in the DC
voltage chart. Perhaps that will help you determine if U3 is defective.
That's all I can think of.

Marshall Jose, WA3VPZ

Treat Hull wrote:

> ....First, I used my scope and verified that I had a good BFO signal to U5
> pin 6.
>
> Then I set up my audio signal generator for about 50 mV peak-to-peak at
> about 1,000 Hz and fed it into the mike connector pins 1 and 7 (which
> I had
> wired for a Radio Shack mike with AF to Pin 1, PTT to Pin 2, and 7 and
> 8 to
> ground).
>
> When I used my scope to trace the AF signal, I started with the K2 powered
> down. I found that I had a strong AF signal all the way to Pin 4 of U3.
> However, when I powered up the K2, I lost all AF at Pin 4 of U3. Working
> backwards, I found that I had AF as far as the junction of C32 and
> C33, but
> no further. It's as though Pin 4 of U3 is going to ground when the unit
> powers up. It behaves the same way with PTT open or closed.
>

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[Richard Kent]

I recently completed K2 Serial No. 5711 and I can testify from first hand
experience that assembly is fun, but that trouble shooting is where you
really learn how it works. I've resolved a few initial problems on my own,
but now I have a persistent problem with SSB which I have been unable to
solve by myself.

 

The symptom is as follows: Monitoring the K2 output with my other radio, an
Icom 706, I have a good signal on CW, but no output on SSB, either voice or
PSK31.

 

For trouble shooting, I first went over all the boards, with particular
attention to the torroid leads on T1 and T2, plus the diodes, per an earlier
posting by Wayne. When everything checked out there, I followed the
procedure recommended in Don Wilhelm's posting of 11 Jun 2006.

 

First, I used my scope and verified that I had a good good BFO signal to U5
pin 6.
 
Then I set up my audio signal generator for about 50 mV peak-to-peak at
about 1,000 Hz and fed it into the mike connector pins 1 and 7 (which I had
wired for a Radio Shack mike with AF to Pin 1, PTT to Pin 2, and 7 and 8 to
ground).
 
When I used my scope to trace the AF signal, I started with the K2 powered
down. I found that I had a strong AF signal all the way to Pin 4 of U3.
However, when I powered up the K2, I lost all AF at Pin 4 of U3. Working
backwards, I found that I had AF as far as the junction of C32 and C33, but
no further. It's as though Pin 4 of U3 is going to ground when the unit
powers up. It behaves the same way with PTT open or closed.
 
Can any shed some light on possible causes that I might investigate further?
 
Thanks in advance,
 
Treat Hull
VA3IMO

Treat are you receiving SSB signals through the op1 filter??

Richard Kent, K2 5296

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