K2 issue

[Vic K2VCO]

Tonight I decided to check out my K2, QRP configuration, for Field Day. I tried it on 40,
20 and 15 meters, and it put out a solid 14-15 watts, drawing about 3.5 amp.

Then suddenly it went dark. The fuse in my rigrunner had blown. Silly me, I had plugged
the K2 into a slot with a 2 amp fuse. I replaced the fuse with a 5 amp one, and started it
up again. But now I can only get about 10w maximum when the power control was turned all
the way up! Current draw is now about 2.15 a.

So, did I blow one of my finals? And if so, could the blowing of the external fuse be the
cause?
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Don Wilhelm-4]

Vic,

Troubleshooting rule #1 - Suspect what you touched last, and resist the
temptation to jump to conclusions.

I would first suspect a voltage drop at the rigrunner (and its fuse)
rather than a failed PA transistor.  Check the voltage at the K2 end
under full current load.
Your 2.15 Amps at 10 watts seems about right, so that is not evidence
enough to declare a bad PA transistor.  I suggest that you remove the
KAT2 (if installed) and operate the K2 directly into a known good 50 ohm
dummy load before drawing any other conclusions.   Test with 13.7 to
13.9 volts at the K2.

You could have a wattmeter anomaly, or if no wattmeter, the load may not
be exactly 50 ohms.

If after taking those steps you still have less than 12 watts output
(10w on 10 meters), then it is time to check the RF voltages (with the
power set to 5 watts) at the Q5 and Q6 collectors. bases of Q7 and Q8,
and the antenna jack and compare those to the values shown in the
Transmit Signal Tracing portion of the manual.  If those are correct and
your maximum power output is still not up to par, then you can suspect
the PA transistors.

73,
Don W3FPR

Vic K2VCO wrote:

> Tonight I decided to check out my K2, QRP configuration, for Field Day. I tried it on 40,
> 20 and 15 meters, and it put out a solid 14-15 watts, drawing about 3.5 amp.
>
> Then suddenly it went dark. The fuse in my rigrunner had blown. Silly me, I had plugged
> the K2 into a slot with a 2 amp fuse. I replaced the fuse with a 5 amp one, and started it
> up again. But now I can only get about 10w maximum when the power control was turned all
> the way up! Current draw is now about 2.15 a.
>
> So, did I blow one of my finals? And if so, could the blowing of the external fuse be the
> cause?
>  
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>
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[Vic K2VCO]

Don Wilhelm wrote:
> Vic,
>
> Troubleshooting rule #1 - Suspect what you touched last, and resist the
> temptation to jump to conclusions.
>
> I would first suspect a voltage drop at the rigrunner (and its fuse)
> rather than a failed PA transistor.  Check the voltage at the K2 end
> under full current load.

Did that. It was 13.1v as shown on the K3's internal meter. This was the same before and
after the 'event'.

> Your 2.15 Amps at 10 watts seems about right, so that is not evidence
> enough to declare a bad PA transistor.  I suggest that you remove the
> KAT2 (if installed) and operate the K2 directly into a known good 50 ohm
> dummy load before drawing any other conclusions.   Test with 13.7 to
> 13.9 volts at the K2.
>
> You could have a wattmeter anomaly, or if no wattmeter, the load may not
> be exactly 50 ohms.

OK, I'll try it. I have a good dummy load and a scope to check the power. Can I set the
KAT2 to CALP or do I have to completely remove it?

> If after taking those steps you still have less than 12 watts output
> (10w on 10 meters), then it is time to check the RF voltages (with the
> power set to 5 watts) at the Q5 and Q6 collectors. bases of Q7 and Q8,
> and the antenna jack and compare those to the values shown in the
> Transmit Signal Tracing portion of the manual.  If those are correct and
> your maximum power output is still not up to par, then you can suspect
> the PA transistors.

OK.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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