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  • Re: MFJ-269 repair (I win)

    From Petr OK1RP@21:1/5 to All on Wed Aug 31 12:48:49 2022
    Hi all,

    anybody here experienced with polarity reversal damage of MFJ-259B please?
    My father damaged it by his mistake and he is totally frustrated so I would like to repair it for him.
    Just want to ask what should be burned and where to start...?

    Thanks, 73 - Petr, OK1RP

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  • From Robert Wilson@21:1/5 to All on Thu Sep 1 14:03:37 2022
    On 8/31/2022 2:48 PM, Petr OK1RP wrote:
    Hi all,

    anybody here experienced with polarity reversal damage of MFJ-259B please?
    My father damaged it by his mistake and he is totally frustrated so I would like to repair it for him.
    Just want to ask what should be burned and where to start...?

    Thanks, 73 - Petr, OK1RP

    Petr,

    There is a schematic at > https://qrzcq.com/pub/RADIO_MANUALS/MFJ/MFJ--259-Ant_Analyser-sch.pdf

    I can see lots of things (e.g. many of the transistors) that could be
    damaged, far too many for me to have any confidence picking them out
    just from that.

    But you could start there for testing components.
    WA9D

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  • From wicklowham@21:1/5 to Robert Wilson on Thu Sep 1 20:22:33 2022
    On 01/09/2022 20:03, Robert Wilson wrote:
    On 8/31/2022 2:48 PM, Petr OK1RP wrote:
    Hi all,

    anybody here experienced with polarity reversal damage of MFJ-259B
    please?
    My father damaged it by his mistake and he is totally frustrated so I
    would like to repair it for him.
    Just want to ask what should be burned and where to start...?

    Thanks, 73 - Petr, OK1RP

    Petr,

    There is a schematic at > https://qrzcq.com/pub/RADIO_MANUALS/MFJ/MFJ--259-Ant_Analyser-sch.pdf

    I can see lots of things (e.g. many of the transistors) that could be damaged, far too many for me to have any confidence picking them out
    just from that.

    But you could start there for testing components.
    WA9D
    ==============================
    Had a look at the schematic as per the above pdf
    Power input is via J1 or from internal batteries
    Reverse polarity protection is by D9, a 4001 SMD diode
    It could well be that this diode is shorting

    Was the unit powered by batteries or from an external supply
    If so , a shorted D9 could have blown the fuse (if any) in the external
    power supply.

    Good Luck with the fault finding

    Frank , EI7KS

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  • From Jeff Liebermann@21:1/5 to rlwilsonjr@charter.net on Thu Sep 1 21:17:17 2022
    On Thu, 1 Sep 2022 14:03:37 -0500, Robert Wilson
    <rlwilsonjr@charter.net> wrote:

    On 8/31/2022 2:48 PM, Petr OK1RP wrote:
    Hi all,

    anybody here experienced with polarity reversal damage of MFJ-259B please? >> My father damaged it by his mistake and he is totally frustrated so I would like to repair it for him.
    Just want to ask what should be burned and where to start...?

    Thanks, 73 - Petr, OK1RP

    Petr,

    There is a schematic at > >https://qrzcq.com/pub/RADIO_MANUALS/MFJ/MFJ--259-Ant_Analyser-sch.pdf

    I can see lots of things (e.g. many of the transistors) that could be >damaged, far too many for me to have any confidence picking them out
    just from that.

    But you could start there for testing components.
    WA9D

    Did he plug the batteries in backwards or apply reverse polarity power
    from an external source into J1 on the above schematic? I don't see
    how it could have damaged much since diode D9 (lower left of
    schematic) should protect the unit from reverse polarity from both
    sources.

    My guess(tm) is that all that happened is that diode D9 did its job
    and shorted out which protected the rest of the circuitry. D9 seems
    to be an SMD component (not sure). Try unsoldering one lead and check
    for a shorted diode with an ohmmeter. Look around for fused traces
    around the power connector and D9.

    I don't know if this will help, but here is some info and experience I accumulated on the MFJ-269. The MFJ-259 and MFJ-269 have similar main
    boards:
    <http://www.learnbydestroying.com/jeffl/MFJ-269-repair/>
    Annotated schematic: <http://www.learnbydestroying.com/jeffl/MFJ-269-repair/mfj-269-schematic.pdf>

    Good luck.
    --
    Jeff Liebermann jeffl@cruzio.com
    PO Box 272 http://www.LearnByDestroying.com
    Ben Lomond CA 95005-0272
    Skype: JeffLiebermann AE6KS 831-336-2558

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  • From David Wade@21:1/5 to Robert Wilson on Fri Sep 2 18:14:36 2022
    On 01/09/2022 20:03, Robert Wilson wrote:
    On 8/31/2022 2:48 PM, Petr OK1RP wrote:
    Hi all,

    anybody here experienced with polarity reversal damage of MFJ-259B
    please?
    My father damaged it by his mistake and he is totally frustrated so I
    would like to repair it for him.
    Just want to ask what should be burned and where to start...?

    Thanks, 73 - Petr, OK1RP

    Petr,

    There is a schematic at > https://qrzcq.com/pub/RADIO_MANUALS/MFJ/MFJ--259-Ant_Analyser-sch.pdf

    I can see lots of things (e.g. many of the transistors) that could be damaged, far too many for me to have any confidence picking them out
    just from that.

    But you could start there for testing components.
    WA9D

    The issue you will have is that if the CPU which is a PIC chip is dead
    the code to re-program it isn't available anywhere, so hopefully it is
    just the protection diode

    Dave
    G4UGM

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