New Antenna Tuner Smoked

Discussion in 'Discussions, Opinions & Editorials' started by KB3ZGV, Nov 13, 2012.

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  1. KB3ZGV

    KB3ZGV Ham Member QRZ Page

    Just great, brand new MFJ 969 and I'm working off the twin lead on 10 meters. I'm just telling somebody how good this thing tunes up. 5 minutes later I swear I heard a little tick, and my meter falls to zero, then I smell it :mad:

    Now it tunes on the coax but not on the balanced line. :(

    I bought it off of HRO in Delaware. Who do you think I'm better off dealing with, HRO or MFJ?
  2. WH2HAO

    WH2HAO QRZ Moderator Platinum Subscriber QRZ Page

    Sorry to hear that. Were you using an amp ? The problem is a replacement MFJ will keep you nervous that it will happen again. See if you can get a different brand from HRO. Dealing with MFJ will probably be filled with frustration, I could be wrong.
  3. KC8VWM

    KC8VWM Premium Subscriber QRZ Page

    Get a Palstar.
  4. K5FH

    K5FH Ham Member QRZ Page

    Looking at the schematic, I suspect you overstressed the balun. Tuners, for some reason, are still rated under the old system. That is, a 300W tuner means it's rated for a transmitter that runs 300W input to the final, meaning that its output is about 150W (assuming 50% efficiency in the final amplifier). So, you shouldn't exceed 150W going into the tuner.

    Another problem is the balun at the tuner's output. Baluns don't handle high reactances very well. What I have seen of MFJ products is that the baluns used in their tuners are pretty light, and should be used with near-resonant antennas (that is, relatively low reactance). You didn't specify what kind of antenna and feedline you were using but I suspect it was highly reactive at the frequency you were using.

    Probably all you need to do is replace the balun. I would recommend using a heftier balun, that is, something wound with larger wire on a larger-diameter core (i.e., a T200-2 core wound with #12 solid). Overkill, yes, but it'll save you from burning it up again.

    Call MFJ. They have a really good warranty policy.
  5. KB3ZGV

    KB3ZGV Ham Member QRZ Page

    Running a 10 meter dipole fed with 300 ohm twin. and only pushing 100 watts.

    I took the cover off and the Balun looks ok. although it does look a bit on the light side. Nothing obviously burned, but there is a slight "stink" . No flash over marks that I could see.

    BTW, I just tested it single wire, and it doesn't tune. I guess that eliminates the balun
  6. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Just saw your new posting that states you cannot tune a single wire after having written a great dissertation on what to do with a cracked balun. As for tuning the wire that would depend on the length of the wire. Do you have a receive signal through the tuner?
    Switching to the dummy load and using the tuner into it can you get the tuner to see and tune the dummy load?
    Check all solder joints. There may be some that are cold or not done at all. MFJ is known for that. You can fiddle around all you want and it won't affect your warranty one bit. MFJ will still honor it.
    Hope this helps
    Last edited: Nov 13, 2012
  7. K5FH

    K5FH Ham Member QRZ Page

    I still think it's the balun. The only way to know for sure is to remove it and test it with an ohmmeter. I'm pretty sure it's a lighweight voltage balun, which isn't the best choice for the application.

    Did you remove the external shorting strap between the balun and the single-wire port? If you leave it in and try to load up a random wire, it's essentially a dead short to ground.

    If it still won't tune after removing the strap, then something is wrong with the multi-position antenna switch - probably a burned or shorted contact.
  8. KB3ZGV

    KB3ZGV Ham Member QRZ Page

    Not much to this thing, but looking at the schematic, and being that the coax works, it's got to be the switch.
  9. KB3ZGV

    KB3ZGV Ham Member QRZ Page

    you beat me to it :)
  10. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Can you tune into the internal dummy load?
    That's a slightly different switch setting as are the coax SO-239 connectors. If you use the center connection it's just like the single wire post except for the switch position.
    The single wire post uses the same switch contact as if you were going to the balun.
    Gheez...I gotta learn how to read. Yup it's the switch. Just contact MFJ and tell them while running 100 watts to the tuner the switch popped. They usually will just send you one and if you're in the mood to put it in then your good to go. If not then you'll need to send it in.
    Hope this helps
    Last edited: Nov 13, 2012
  11. K5FH

    K5FH Ham Member QRZ Page

    I just opened up my MFJ-949E (essentially the same as the 969 except the 949 uses a tapped inductor) and replacing the switch is going to be a real bear because of the way it's mounted and soldered to the circuit board. You'll essentally have to totally dismantle the tuner and rebuild it. Even for such a simple design that's going to be a lot of work.

    Try getting MFJ to send a new tuner in exchange for the old one, if possible.
  12. N8CPA

    N8CPA Premium Subscriber QRZ Page

    What he said. Call MFJ, talk to Jamie, he will likely offer such an exchange.
  13. W3WN

    W3WN Ham Member QRZ Page

    I would call HRO first, since they sold it to you, and see what (if anything) they can or will do.

    If they're willing to exchange the unit as defective, or issue you store credit, considering you only just bought the unit... well, I'd use it to purchase another brand.
  14. KO6WB

    KO6WB Premium Subscriber QRZ Page

    The replacing the switch was just a suggestion with a hint that the OP would need to be in the mood to do that. Who knows? Maybe it'll be something to do.
    Time is short for taking it back to HRO. That'll work. All you have to do is tell them the MFJ tuner is a piece of junk. They'll believe that and if they seem to balk then just tell them you want to spend more money on something else provided they take that one back. Usually it's not a problem though.
    Have fun
  15. EA4TA

    EA4TA Guest

    If given the option, my automatic 993B has seen heavy usage, severely missmatched antennas, and continuous button port switching since I bought it.

    I even use to tune the 160 m. band on my CB antenna (later used for RX).

    It is my most abused piece of gear. (And I got to love the relay clicking noises it makes).
  16. N6MEJ

    N6MEJ Ham Member QRZ Page

    I've got to agree with those that suggest dealing direct with MFJ. Anytime I've called, the customer service has been excellent...better even than their product usually is. If HRO is close, and you don't want to wait, it can't hurt to call them first.
  17. KB3ZGV

    KB3ZGV Ham Member QRZ Page

    It's got to be the switch, it was working on everything but random/balanced, after looking at the schematic and looking inside, I switched it over to the bypass position and hooked my twin lead fed dipole up again, I transmitted on my antenna's resonant frequency. The SWR/power meter functions worked, and the baln was still in the circuit so that eliminated them. So I turned the switch back to random/balanced going through the tuning and it worked.

    Moving the switch must have cleared whatever kind of open or fault was going on inside it, because now it's back to working beautifully. I just worked 160M on a random wire, and it tuned to 1;1 without a problem. Same thing with my twin lead fed 10 M dipole using the baln.

    Last night when I heard that little arc and smelled the smoke it acted like something was blown open. Now I can't get it to malfunction again.
  18. N0SYA

    N0SYA Ham Member QRZ Page

    Admit it, 11m was soooo much easier than all this high technology ham stuff.
  19. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    If you bought it new, it's too young to smoke.

    The Surgeon General's warning should be on the package somewhere.
  20. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    I know ALL ABOUT that Tuner Switch!!!

    I had a lightning strike and it blasted that switch. MFJ was called and I ordered a new switch.
    Cost me $15!

    What was sent to me was a USED switch they pulled out of some other unit. It turned out to have OPEN CONTACTS!

    I tore apart the blasted switch, cleaned the contacts, filed them down and reinstalled that one.

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