Mirage B3060 Brown face burnt circuit

Discussion in 'Amateur Radio Amplifiers' started by N8ZI, Aug 20, 2019.

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  1. N8ZI

    N8ZI XML Subscriber QRZ Page

    I'm repairing a Mirage B3060 Brown face that was reportedly inoperative. It seems to work fine except for 2 issues.

    1) The amp will put out full power on the high end of 2M (146-148) but around 40w less on the low end (144-145). How can I average it out over the entire FM portion or even the whole band?
    2) During a visual inspection I found a wire or what might have been a component burnt off between the Antenna socket ground and the circuit board. See attached photo. I pulled the wire further apart for a better view. The original burnt gap was approximately 1/16"+/-.

    This amp is used by my Dad who has a bad habit of disconnecting the coax from the radio which still leaves the amplifier and SWR/power meter connected to the antenna. I keep suggesting he just disconnect the antenna coax from the meter, thus removing all components and isolating the antenna, but he never listens to common sense :(
    He did have severe thunderstorms in the area, so the burnt area might be related yet the meter and amplifier still function.

    I checked online for a schematic and only found a copy on the BAMA site that was blurry and somewhat chopped off where I need to view it.
    Mirage/MFJ website doesn't go back far enough for this amp and the newer amps are not showing what I need.

    Can anyone clue me in to whether this was a simple wire or possibly a diode? Is there a better schematic out there? I have read articles mentioning a 4 page schematic/manual but the links are dead.

    Any ideas to even out power output across the band?

    Thanks in advance.
     

    Attached Files:

  2. WB3BEL

    WB3BEL Ham Member QRZ Page

    I don't see anything obviously wrong in the area you indicate. Just looks like the end of the ground with some leftover solder flux in that area. I don't think this is a problem.
    Or maybe I am not seeing what you are seeing.

    These kind of amplifiers do have some input/output matching capacitor adjustments. They usually are set fine from the factory, but someone may have "adjusted" them without knowing what they are for.

    Another common problem with these is that the input match is not that great and often they can be optimized by making slight changes to the length of coaxial cable connecting them to the transmitter. Make sure that jumper coax is a good quality 50 Ohm cable. That it does not have a broken ground, or other problem which also can create some weird performance.

    Or the transmitter you are driving it with has variable output power over frequency which is creating some of the difference in power. You could check it by moving the wattmeter temporarily to the output of the transmitter, while providing a good termination to the output of the transmitter or power amplifier, depending on whether you are testing standalone, or with both the transmitter and amp.

    Make sure that you are testing it with an accurate wattmeter and with a dummy load suitable for VHF operation.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I never heard of a B3060.

    Do you mean B3016?

    If you do mean B3016, the "missing component" which is normally soldered across the ANTenna connector is a 2 pF capacitor.

    There are tuning adjustments at the input and output of the amplifier (trimmer capacitors) which can be adjusted for "gain flatness," and normally are at the factory when it's new, but that's done into a perfect 50 Ohm dummy load and when you change to a real antenna, things change.

    Schematic:

    B3016 schematic.PNG
     
    Last edited: Aug 20, 2019
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    Test using a dummy load.
     
  5. N8ZI

    N8ZI XML Subscriber QRZ Page

    It is difficult to see but there is a wire about the same diameter as resistor leads soldered to the circuit board on the bottom and the coax shield at the Antenna output. I will add a better photo for clarification.

    Yes I checked both the input and output SWR across the entire 2M band with 2 different SWR/power meters even swapping their positions. Everything is fine except output power. One of them was inline when the amplifier stopped functioning so swapping it around in the line verified it still functions normally.
    Yes I checked it into a UHF/GIF dummy load and also a vertical and dual 9 element yagi phased. It is the same on all loads. 40w is a lot to lose across the 2m band.

    Perhaps you can see the burnt off wire better in this photo.
     

    Attached Files:

  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    See post #3, I told you what the missing component was. It's also on the schematic, clearly shown.
     
  7. N8ZI

    N8ZI XML Subscriber QRZ Page


    Yes it is a Mirage B3016.
    Sure would be nice if it was a 30w in 600w out amplifier :)
    The resister is still intact soldered between center conductor and shield. The shield is also soldered to that ground lug which is attached to the Antenna connector ground and another lead comes from the resister, coax shield, ground lug down to the circuit board. That is the burnt wire and my concern. See attached photo.
     

    Attached Files:

  8. KA9JLM

    KA9JLM Ham Member QRZ Page

    Looks like the cap smoked. :eek:

    That is a inductor, Not a resistor and the cap across it toasted.
     
  9. WB3BEL

    WB3BEL Ham Member QRZ Page

    Yes, that view is much clearer. I checked a 3016 I have here, and that burned part is just a piece of Buss wire tying the connector ground lug to the PC board.
    Maybe it is as you say some lightning damage, but it looks strange.

    As KA9JLM indicated that component across the connector is just an inductor that is supposed to provide static discharge. I does not look like it is damaged, but you might check it for continuity.
     
  10. N8ZI

    N8ZI XML Subscriber QRZ Page

     

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