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 Post subject: HR-50 power reduction
PostPosted: Mon Mar 26, 2018 2:47 pm 
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Joined: Mon Mar 26, 2018 2:17 pm
Posts: 3
I have been using the HR-50 for a couple weeks with good results on all bands up to this past week when I began getting erratic power out put on 20-10 meters. 17 meters is the worst. I check the different posts and performed the 30M-40M check on the relay capacitors which showed everything was correct. Then I zeroed out VR1-VR4 and tried to rest the bias and was not able to get a proper reading - only a maximum of 120 on VR1 and 196 on VR2 and no further attempts.

The initial problem appeared after using the amplifier with the temperature reaching close to 100 degrees. So, it seems to be a temperature related issue.
Associated with the initial output problem the receive signal on the KX3 was attenuated by 3 s-units.

I have the internal tuner and the qsk boards installed. I performed my test with the tuner board removed.

When the amp was working correctly, I was using 1.4W drive with the KX3 and getting 50+W out on all bands.

Leo NK8L


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PostPosted: Tue Mar 27, 2018 10:37 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1135
Hi Leo,

the vast majority of temperature related issues with the Hardrock amp are issues with the MOSFETs not making good thermal contact with the heatsink. The fact that you are unable to set the bias now indicates that the MOSFETs may be damaged.

The only confusing item is the loss of RX signal. That indicates something in the QSK board which could make the power output erratic but would have no effect on the ability to set the bias. Perhaps there are multiple issues. On the QSK check to see if the board is seated in the mating connectors properly. Sometimes filing down the spacers a little makes for a more reliable connection.

If you can't figure it out, you can send it in for a check-up.

73,
Jim WA2EUJ


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PostPosted: Tue Mar 27, 2018 7:03 pm 
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Joined: Mon Mar 26, 2018 2:17 pm
Posts: 3
Jim, thank you for your quick reply. I will take you up on the offer to send the amp in for a check.
Please e-mail me the address.

Leo NK8L


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PostPosted: Thu Mar 29, 2018 5:08 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1135
Just send to my QRZ.com address. I recommend a Medium Flat Rate box from the USPS.

73,
Jim WA2EUJ


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PostPosted: Thu Mar 29, 2018 5:08 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1135
or send an email to jim (at) hobbypcb (dot) com


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PostPosted: Thu Mar 29, 2018 9:03 am 
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Joined: Mon Mar 26, 2018 2:17 pm
Posts: 3
I sent the amplifier out yesterday using the Hobby PCB address in Clearwater. I did use the medium box.

I am curious as to what will be found. I did remove the main board to work on it when I installed the QSK board. I used a silver heat sink compound when I reinstalled the main board. The impression on the heat sink showed the amplifier transistors was having total contact with the surface.

Leo NK8L


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PostPosted: Thu Mar 29, 2018 5:52 pm 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1135
Unfortunately I'm near Baltimore, the Clearwater address is the shipping department. They will probably send it back to you without an RMA.

Jim.


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