K2-100 Xmit Problem

[Jack Shrawder]

I'd appreciate suggestions that might help me isolate a problem that  
I believe to be in the KPA100. Receive is fine on all bands.

My K2/100 has been working wonderfully for three years. Now,  
suddenly, a problem appears on both on low and high power settings on  
160-10mtrs.  K2 Display shows, high current (briefly), high swr and  
much below requested power even when feeding a 50 ohm dummy load.  
Basic K2 checks out OK on RX and TX on all bands with QRP top installed.

The only section shown in the KPA100 schematic that would appear to  
alter the desired rf flow in both low and high power settings would  
be the SWR Bridge. No burned components visible so far. If the SWR  
section is a likely candidate, would it be correct to suspect first  
D16 and D17? Or could the T-R switch section be at fault based on  
some of the anomalous voltage readings present.

Have completed voltage reading of D1-D14 and Q1-Q12 and U1-U7.  Q4  
and Q5 show lower than expected readings on TX. Other readings of  
note: D7 -20 volts Anode and +19 volts Cathode, and D8 20 volts Anode.

Any suggestions for proceeding would be appreciated,

73, Jack, KT6JS

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[Don Wilhelm-3]

Jack,

Since the problem shows up on both low and high power, you are correct in
believing the problem may be with the wattmeter, but do some preliminary
chaecks first.  The only other things that could be wrong are the Low Pass
Filters (unlikely if it worked for 3 years) or the relays not operating.

Both Hi Cur messages and High SWR indications may be the result of a
non-operating relay.  Switch to low power and check continuity between the
J1 'RF IN' point and the center of the SO-239 - if that shows open, there is
a relay or LPF problem to be found.  Sometimes you can have receive through
the path without full continuity - you just didn't notice the signal
reduction - the continuity checks are quick and easy.

Then check the voltage at U1 pin 1 - if the voltage is near 5 volts, then
the relays should be getting control voltages to them.  If there is not 5
volts, check the regulator.

If the checks above indicate all is well, then yes the wattmeter is the most
likely to blame.  Other than the diodes in the wattmeter, U5 and U6 could be
suspects as could Q10 and Q11.

73,
Don W3FPR

> -----Original Message-----
>
> I'd appreciate suggestions that might help me isolate a problem that
> I believe to be in the KPA100. Receive is fine on all bands.
>
> My K2/100 has been working wonderfully for three years. Now,
> suddenly, a problem appears on both on low and high power settings on
> 160-10mtrs.  K2 Display shows, high current (briefly), high swr and
> much below requested power even when feeding a 50 ohm dummy load.
> Basic K2 checks out OK on RX and TX on all bands with QRP top installed.
>
> The only section shown in the KPA100 schematic that would appear to
> alter the desired rf flow in both low and high power settings would
> be the SWR Bridge. No burned components visible so far. If the SWR
> section is a likely candidate, would it be correct to suspect first
> D16 and D17? Or could the T-R switch section be at fault based on
> some of the anomalous voltage readings present.
>
> Have completed voltage reading of D1-D14 and Q1-Q12 and U1-U7.  Q4
> and Q5 show lower than expected readings on TX. Other readings of
> note: D7 -20 volts Anode and +19 volts Cathode, and D8 20 volts Anode.
>
> Any suggestions for proceeding would be appreciated,
>
> 73, Jack, KT6JS
>
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