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Radio powers down when transmitting

I have a flex 6300. I have had this radio several years and no problems. Recently sporadically when i transmit the radio will shut completely down . i have to turn it back on. the swr looks good. not sure why it started doing that. any ideas? rf?


  • Erik Carling EI4KF
    Erik Carling EI4KF Member ✭✭✭

    Power supply and input voltage whilst in TX?

  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator

    Also, try running FRStack or K9DUR’s Flex Monitor to monitor the voltage in the radio, both at the entrance to the radio and to the PA.

    The 6300 has an internal blade (ATX style) fuse. The socket to fuse blades can develop resistance over time causing a voltage drop. Also oxidation on the Power Pole connections can also cause a voltage drop.

    Running either utility and start with tune power around 25 watts. Measure voltage at connector outside radio using a volt meter. Then use either utility to monitor voltage on receive then during transmit. Record the voltage drop. Increase tune power to 50 and repeat, then 100. If you have either issue then it should be apparent in the recorded voltage drop.

    You can clean the blades of the internal fuse and carefully increase tension on the sides of the fuse socket. Also clean the Power Pole metal connections and insert and remove the power plug several times to help clean the contacts.

    Last, the radio should be connected direct to power supply and not through a Rig Runner.

    73 Dave wo2x

  • Al_NN4ZZ
    Al_NN4ZZ Member ✭✭✭

    Had the same issue...documented the fix on my web page.


    Regards, Al / NN4ZZ

    al (at) nn4zz (dot) com

    6700 Win10 Pro V2004 -- SSDR V2.4.10

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Generally, when it powers down, the radio detected some sort of 'brown out'. So, that is the symptom and now you'll need to figure out exactly why.

    Some of the culprits are:

    • RFI due to some reason - changing cables and adding chokes can help
    • Voltage Drop between the radio and the power supply. Every connection can contribute when under full load. It can be corrosion on the Power Poles, Fuses, etc., and it only takes about 1 ohm of resistance to make this happen when under full load and drawing 20 amps
    • The power supply can't supply a full 14V at 20amp load anymore

    Feel free to open a support ticket if required if you need assistance.


  • Tim K9WX
    Tim K9WX Member ✭✭✭

    Has anyone had the need to reach the fuse on a 6600?

    The hardware reference manual says, "In the event you ever need to replace the internal fuse, remove the top cover and locate the fuse in the rear corner of the PA board just inside the case adjacent to the Anderson Powerpole connector." But the fuse is not visible with the top cover removed. It looks like at least two boards would have to be removed before I could get to the backside of the Powerpole by going down through the top. I wondered if access would be cleaner with the bottom cover removed, but thought I would ask here first before I started digging, in case there is an easier path.

    Tim K9WX

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Tim, the fuse is not accessible from the bottom due to the shield plate. You do need to remove the two boards on the top to get to the fuse. Not difficult, just a bit tedious. My 6400 has no ATU, so I only had one board to remove to get to mine.

  • AG4Q
    AG4Q Member ✭✭

    Tim, I found it easier to remove the back of the chassis. There are a lot of screws to remove, but found it easier than removing the two boards to access the 30A fuse.

    Randy Nash


  • K5XH
    K5XH Member ✭✭

    Hi Clint.

    Hope you got your problem resolved. I'll pass along an experience that I had with my 6600 a couple of years ago. I was having the same problem. If I set the radio to 100 watts and sent a dot on CW the radio would shut down and reset. My first thought was a power supply issue. I had two Astron linear supplies. Both were 35 amp supplies. I had the same problem with either supply. The voltage at the radio measured OK when I brought the power up slowly but if I tried to send a dot at 100 watts it would fail. I actually sent the radio back to Austin TWICE because of this problem. They could not replicate the problem. Also considered was the possibility of RF in the shack. I completely overhauled my grounding and added more chokes on all the auxiliary cables. Nothing seemed to help.

    The solution was to replace the Astron supplies with a new 50 amp switcher! BOTH my old Astron supplies had a problem with suppling the sudden current demand. They would work fine on SSB but not CW (or FT8 - RTTY).

    I should have gone with my first instinct and bowered a different supply from someone and verified the solution.

    73, Mark K5XH

  • Tim K9WX
    Tim K9WX Member ✭✭✭

    I ended up going down from the top and removing both boards. Was not particularly difficult.

    My goal was to improve the voltage drop seen by the radio when it is key down. In the hope of improving the power out when the radio is set to transmit at maximum RF power.

    There was some modest corrosion/oxidation on the legs of the old fuse. Which probably also means there is a similar condition on the fuse holder but I could not see any good way of cleaning those. My radio is 4 years old and the fuse is the original fuse.

    With the old fuse I was seeing an internal voltage at key down as low as 11.05 volts; with the new fuse I now see an internal voltage as low as 11.3 volts. So, a modest improvement, as measured by the K9DUR SDRMonitor software. The power supply shows rock-steady (an Astron RS-35M) and I am using the Flex-supplied factory cable with 45 amp PowerPole connectors directly to the radio, so I am not sure what else I might do to minimize voltage drop. I believe I am seeing a very modest improvement in the transmitted RF power but I don't have a confident way to measure it so I say that with caution.

    One word of caution for anyone trying this: the fuse in my 6600 is an mini fuse. It is not the larger style fuse used in RigRunners or other power strips common to the hobby. The terminology for these fuses is somewhat confusing and the 6600 hardware reference manual simply says, "The power input has a protective 30 Amp automotive “blade type” fuse inside the radio case." Make sure you have the right size replacement fuse on hand before you start. Here is a table of automotive fuse styles from Wikipedia. Lots of different was of referring to the same fuse.

    Tim K9WX

  • Al_NN4ZZ
    Al_NN4ZZ Member ✭✭✭

    Hi Tim,

    What is the voltage set to / measured on you power supply?

    I found on my 6700 that setting it to 15 volts on the supply helps and is within the acceptable range at the radio.

    • Astron RS-35M voltage adjusted to 15.0 Volts at the rear of the power supply which reads about 14.97 at the radio powerpole connector. 
    • The SDRMonitor now reads 14.6V on RX and 14.2 on TX.   The drop between the powerpole and SDRMonitor at TX is about 0.8V.

    Regards, Al / NN4ZZ

    al (at) nn4zz (dot) com

    6700 Win10 Pro V2004 -- SSDR V2.4.10

  • Tim K9WX
    Tim K9WX Member ✭✭✭

    The voltage on the power supply (an RS-32M-AP) measures 13.9 with a VOM on the rear terminals and shows about the same on the front panel meter. The K9DUR software shows 13.62 inside the Flex in RX.

    I see nothing on the back of the power supply, on the outside of the case, that looks like a voltage adjustment. Is the voltage adjustable on this model?

    Tim K9WX

  • Geoff AB6BT
    Geoff AB6BT Member ✭✭✭

    Teh RS-35M is internally adjustable:

  • Al_NN4ZZ
    Al_NN4ZZ Member ✭✭✭


    There is a link on my web page to a good step by step article on how to adjust the RS35 voltage. Scroll down to the "steps taken" section


    Regards, Al / NN4ZZ

    al (at) nn4zz (dot) com

    6700 Win10 Pro V2004 -- SSDR V2.4.10

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