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 Post subject: I overheated it!
PostPosted: Sun Oct 18, 2015 8:05 pm 
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Joined: Sun Dec 01, 2013 8:44 pm
Posts: 11
I was having a Domino (Keydown digital mode) QSO today on 20 meters. It was a ragchew. I wasn't paying any attention to the heatsink temp. After about 45 minutes of ragchewing, the other op reported heavy QSB, I hadn't noticed any. I looked at the heatsink temp; it was 205'F!! Whoops!! Usually I have a small fan sitting on top of the heatsink and the temp never gets over 150'F...

Hardrock 50 Serial #1183 (or 1189? )
160=35 watts
80=52
40=42
30=51
20=13
17=5
15=9
12=8
10=6
6=9

A physical inspection shows RLY 12 is pretty well bulged. I know this isn't probably a great test but I backed off VAR 1-4 and reset the bias as per instructions...to my thinking this means the finals are all still okay as I was able to set at 25 mA, 50, 75, 100 etc...

I prefer to check current draw from the amp with my current clamp which I left at work.

I am tempted to just throw new RLY 12-15 into and see what happens.

What else should I test?

Tim


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 Post subject: Re: I overheated it!
PostPosted: Mon Oct 19, 2015 6:37 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1142
Hi Tim,

Which version of the firmware are you running? We made a change in 3.0D that sacrificed a little gain for reduced internal dissipation. So once we get you back up and running try updating the FW and setting the bias higher 150mA per device and it won't happen again.

It looks like what happened is RLY12-RLY14, or some subset, are now permanently connecting C5, C7, C31 and or C33 into the circuit which messes up the output on the higher bands. What I recommend is replacing all of them. Send me an email with your mailing address to jim (AT) HobbyPCB (dot) com and I'll make you a care package with 4 new relays and four replacement caps.

If you don't think you can replace the SMT caps you can send me the amp and I'll fix it for you.

73,
Jim WA2EUJ


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 Post subject: Re: I overheated it!
PostPosted: Mon Oct 19, 2015 12:10 pm 
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Joined: Sun Dec 01, 2013 8:44 pm
Posts: 11
Hi Jim, email sent. Thank you as always for your help!


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 Post subject: Re: I overheated it!
PostPosted: Mon Nov 02, 2015 2:22 pm 
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Joined: Sun Dec 01, 2013 8:44 pm
Posts: 11
I got the parts on the board finally, thank you very much for taking care of me...
Am I to set the bias at 150 mA per device, or an additional 150 mA (=175)?

Thanks!
Tim


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 Post subject: Re: I overheated it!
PostPosted: Mon Nov 02, 2015 10:21 pm 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1142
Hi Tim,

When I set the bias on an amp, I use 150-300-450-600 and that seems to work great.

73,
Jim WA2EUJ


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 Post subject: Re: I overheated it!
PostPosted: Mon Nov 02, 2015 11:24 pm 
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Joined: Sun Dec 01, 2013 8:44 pm
Posts: 11
Cool, thanks Jim!

Tim


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