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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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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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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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

--- SoupGate-Win32 v1.05
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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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