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Author Topic: Problem with MFJ-259B analyzer  (Read 3209 times)
WS4T
Member

Posts: 182




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« on: February 26, 2012, 03:49:31 AM »

I've had an MFJ-259B analyzer for about 2 years. It worked fine at first, but then starting last summer, I had to apply pressure to the coaxial connector to avoid an infinite SWR. Sounds like a bad connection in the antenna socket (SO-259), no?

So I took it apart and tried to find a bad solder joint, but no luck.

I know these analyzers have a bad history of quality control problems, so maybe somebody else has had the same problem and managed to fix it? Any ideas?

Thanks,
Gary, ES1WST
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K1EJA
Member

Posts: 9




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« Reply #1 on: February 26, 2012, 06:14:48 AM »

Well as a possibility..
I had a similar problem.. I found that 259 plug diameter I was using was slightly smaller than the opening of the so239 connector.  The infinite SWR showed up only when the 259 plug was firmly attached and straight into the opening.  Unscrewing it slightly made contact as the center post was no longer squared with the center opening.  This was a problem with the  259 plugs that are crimped and tapered at the end. 

Ray

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W5FYI
Member

Posts: 1046




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« Reply #2 on: February 26, 2012, 07:29:24 AM »

Take another good look at the solder connection--chances are there's a a hairline crack on the p.c. trace.  I would solder a piece of multistrand wire from the center conductor of the socket to the PC board, maybe making a little "u-turn" in the wire to avoid future wire stresses.  By that I mean use multistrand wire to connect the socket to the p. c. board, both on the center   connection socket and on the outside (ground) connection.
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WS4T
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Posts: 182




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« Reply #3 on: February 27, 2012, 01:33:01 AM »

Thanks for the input! Both of those ideas are plausible -- I will look at it more.
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KE3WD
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Posts: 5689




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« Reply #4 on: February 27, 2012, 10:58:31 AM »

A fairly common problem with many SO-239 designs is that the center fingers can be spread rather wide by the insertion of certain types of PL-259 plugs and then when you insert another design of PL-259 that has a slightly smaller diameter center pin, the connection is now intermittant. 

So if you resolder the jack inside (recommended way of testing, btw) and the problem persists, inspect the center of that SO-239 and also the pins of your various PL-259s to see if that isn't what's going on here. 

Sometimes SO jacks that have those four fingers with slots in between can be tightened a bit by carefully inserting a very tiny jeweler's screwdriver between them and the insulator, bending them towards center a very wee bit to make them connect again. 

Worst case scenario means obtaining a new SO socket of good and durable design and replacing the one on the unit. 

Sometimes the problem only lies in the plug at the end of the jumper as well.  Some of the factory made crimp-type that have a smaller diameter pin on the PL are simply not able to do the job.  Toss it, or solder a good PL plug on the end instead. 

73
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WA3SKN
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Posts: 5526




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« Reply #5 on: February 27, 2012, 12:59:33 PM »

Try not to damage the diodes while working on it.  They do not take much abuse.
73s.

-Mike.
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KG6YV
Member

Posts: 515




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« Reply #6 on: February 27, 2012, 01:56:34 PM »

Same issue with my 259B

I also found the MFJ SO239 to be very loose and had intermittent connection issues.  I replaced it with a quality connector.   Also, tightened the screws holding the SO239 into the case.  No more issues.
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W5DQ
Member

Posts: 1209


WWW

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« Reply #7 on: February 27, 2012, 02:10:34 PM »

I've had an MFJ-259B analyzer for about 2 years. It worked fine at first, but then starting last summer, I had to apply pressure to the coaxial connector to avoid an infinite SWR. Sounds like a bad connection in the antenna socket (SO-259), no?

So I took it apart and tried to find a bad solder joint, but no luck.

I know these analyzers have a bad history of quality control problems, so maybe somebody else has had the same problem and managed to fix it? Any ideas?

Thanks,
Gary, ES1WST

I just had to replace the SO-239 in my MFJ-259 as it had the same problem. The center pin socket tends to get stretched out and doesn't make a good solid contact with the center pin of your coax. It isn't hard to swap out the connector but does require some familiarity with dis/re-assembly techniques and soldering. Took about 20 minutes from case open to case closed and back good as new.

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
KB1GMX
Member

Posts: 815




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« Reply #8 on: February 27, 2012, 06:54:59 PM »

Had the same connector issue.  My solution was to put in a quality type N connector.  It fit in
the same place and hole and is less prone to that failure.  Then I use a N to PL adapter, 
N to SMA N to BNC, N to TNC, or N to Binding post, as I use all of them.  For me it solved
the problem and also prevents the problem of inexperienced users grabbing mine at field day.


Allison
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W5DQ
Member

Posts: 1209


WWW

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« Reply #9 on: February 28, 2012, 10:29:22 AM »

Had the same connector issue.  My solution was to put in a quality type N connector.  It fit in
the same place and hole and is less prone to that failure.  Then I use a N to PL adapter, 
N to SMA N to BNC, N to TNC, or N to Binding post, as I use all of them.  For me it solved
the problem and also prevents the problem of inexperienced users grabbing mine at field day.


Allison

Good idea on the N connector. They use N's on the 269 series. I may have to go back and redo my recent repair.

As to having someone else 'grab' my gear, that doesn't happen because I keep my stuff under lock and key and if someone needs to use it, they ask first. I can't afford to replace my gear when some 'inexperienced' well-intended newbie grabs it and turns it into a paperweight. No bad feelings towards anyone, I just control access to my gear and have no problems.

Gene W5DQ
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
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