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 Post subject: ATU on fire
PostPosted: Wed Oct 21, 2015 1:31 pm 

Joined: Mon Apr 20, 2015 2:07 pm
Posts: 13
My ATU is putting out tiny flames under the RF_OUT connector on the PCB!

(between the connector and the board)

At first I thought the connector was the problem, so I took it out. The connector had almost turned into charcoal underneat.

I had one extra green connector in my kit so I replaced it. Before replacing I scraped everything clean and wiped it down with isopropanol.
Tried to solder it back on today, but the result is the same:

ATU catches fire while sending and open flames are coming out from underneath the connector.
I believe my project is toast - literaly :(

Started out as a fun project with HR50 w/QSK + ATU. After assembly I have had intermittent problems with random clicking in the relays and loss of output power. I have been unable to find the cause of these issuer but it was obvious that I had RF issues somewhere.

Not sure where to go from here...

LB1JG - Arnfinn

 Post subject: Re: ATU on fire
PostPosted: Wed Oct 21, 2015 7:58 pm 

Joined: Mon Jul 23, 2012 6:25 am
Posts: 1143
Hi Arnfinn,

Sorry to hear about your flaming ATU. But there is a lesson here:

If your ATU relays are chattering with the modulation, you have an RFI problem!!!!!

You need to:

1. Provide a better ground.
2. Make the transmission line longer.
3. Move the amp away from the antenna.
4. Put RF chokes on the power/control/antenna cables.
5. Decrease the power until the relays stop chattering.

I tested the ATU into every load from 12-600 ohms and the HR50+ATU is a solid performer when everything is properly grounded.

There must have been some very high voltage under the output jack to get flame, it's rated at 2 kV. Perhaps there was some flux residue.

If you want to send me your ATU I'll be happy to repair it but unless you address the system level RFI issues, it may go up in flames again.

Send me an email jim (at) hobbypcb (dot) com and I can send you my shipping address. It's good in QRZ.com


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