K2 BFO problem, need JFET advice

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K2 BFO problem, need JFET advice

N4TY
Symptom:

K2 with very low audio output, only the strongest stations can be copied.
Have eliminated the BPF, attenuator, pre-amp, and so forth with signal tracing.
Transmit stops increasing at about 4W, the control runs out of effect.
So the K2 is alive, but something is wrong in the signal path.

The BFO area was redone with a mod (which I have no paperwork on, somebody else's radio).
The components were dead-bugged onto the area around the T33 BFO toroid, and I believe they shorted out on the bottom cover.
Using the included kit RF probe, test point TP2 has only 1 millivolt on it, but Q24 has about 0.4Vrms on the gate, which is fed from U11 pin 6 and through the BFO components.

Thus, it appears to be a blown Q24, which is a JFET  J310.
Radio Shack has a MPF102, would that be OK to use?
I've checked the respective datasheets of J310 vs MPF102, and I haven't found much difference in ratings, even the noise figure is about the same.

Your comments appreciated ASAP!

73, Tyler N4TY

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MCU LD

W4GRJ
I think I have a real mess up here. I did the latest firmware update and all
seemed o.k. until I tried to transmit. I have no audio at all. Thinking it
could be the mike, I put the original K3 mike on with same results. O.K.,
all I did was a firmware update so I decided to back rev to previous
version....my lovely K3 choked and shut down during the first part of the
upload. Now all I get is a blinking red power led and MCU LD in the display.
I tried the reset procedure, holding the power button for 10 sec without
success. The utility does not recognize the radio is connected. Appreciate
suggestions to fix short of sending the radio back.

Tnx,
Jack
W4GRJ

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Re: MCU LD

Don Wilhelm-4
  Jack,

Just holding the power button for 10 seconds is not sufficient.
Go to the K3 Utility Help file, and click on Troubleshooting.
 From there, select Forcing the K3 into "Firmware Load Required" Mode
Then follow ALL the instructions shown.

73,
Don W3FPR


On 7/1/2011 10:55 AM, W4GRJ wrote:

> I think I have a real mess up here. I did the latest firmware update and all
> seemed o.k. until I tried to transmit. I have no audio at all. Thinking it
> could be the mike, I put the original K3 mike on with same results. O.K.,
> all I did was a firmware update so I decided to back rev to previous
> version....my lovely K3 choked and shut down during the first part of the
> upload. Now all I get is a blinking red power led and MCU LD in the display.
> I tried the reset procedure, holding the power button for 10 sec without
> success. The utility does not recognize the radio is connected. Appreciate
> suggestions to fix short of sending the radio back.
>
> Tnx,
> Jack
> W4GRJ
>
>
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Re: MCU LD

Mike Reublin
In reply to this post by W4GRJ
Jack -

The first step in the K3Utility help is to disconnect the K3 from the power supply
for at least 30 seconds, maybe longer. In the K3 Utility, bring up the help file, and
type force into the search box, then click on the List topics button for a step by step.

HTH!

73, Mike NF4L

On 7/1/2011 10:55 AM, W4GRJ wrote:

> I think I have a real mess up here. I did the latest firmware update and all
> seemed o.k. until I tried to transmit. I have no audio at all. Thinking it
> could be the mike, I put the original K3 mike on with same results. O.K.,
> all I did was a firmware update so I decided to back rev to previous
> version....my lovely K3 choked and shut down during the first part of the
> upload. Now all I get is a blinking red power led and MCU LD in the display.
> I tried the reset procedure, holding the power button for 10 sec without
> success. The utility does not recognize the radio is connected. Appreciate
> suggestions to fix short of sending the radio back.
>
> Tnx,
> Jack
> W4GRJ
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>


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Re: K2 BFO problem, need JFET advice

Don Wilhelm-4
In reply to this post by N4TY
  Tyler,

Since you have low audio output during receive, I would suggest you are
looking in the wrong place.
Q24 is not involved during receive, and will show no signal at TP2
during receive.

The 400 mV at the gate of Q24 is just fine.  Put the K2 menu into CAL
FCTR and then check the RF level at TP2 - it should be somewhere between
25 and 70 millivolts.

You may be in for some Signal Tracing.  Use the steps found in Appendix
E of the manual.

On 7/1/2011 10:45 AM, Tyler Barnett wrote:

> Symptom:
>
> K2 with very low audio output, only the strongest stations can be copied.
> Have eliminated the BPF, attenuator, pre-amp, and so forth with signal tracing.
> Transmit stops increasing at about 4W, the control runs out of effect.
> So the K2 is alive, but something is wrong in the signal path.
>
> The BFO area was redone with a mod (which I have no paperwork on, somebody else's radio).
> The components were dead-bugged onto the area around the T33 BFO toroid, and I believe they shorted out on the bottom cover.
> Using the included kit RF probe, test point TP2 has only 1 millivolt on it, but Q24 has about 0.4Vrms on the gate, which is fed from U11 pin 6 and through the BFO components.
>
> Thus, it appears to be a blown Q24, which is a JFET  J310.
> Radio Shack has a MPF102, would that be OK to use?
> I've checked the respective datasheets of J310 vs MPF102, and I haven't found much difference in ratings, even the noise figure is about the same.
>
> Your comments appreciated ASAP!
>
>
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