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Author Topic: mfj 259b gone mad  (Read 570 times)
M0JHA
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Posts: 646




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« on: February 03, 2008, 12:33:00 PM »

hello,
      my antenna analyser has just gone down..  it powers up shows frequency,swr.. R=0 all the time and X doesnt show at all on the lcd display..the needle on the impedence meter on the front doesnt move at all..but the swr does...

i was getting a match through an atu to antenna with the analyser in line.. i disconnected the analyser and sat it on the bench.. connected the coax to my 4m radio and gave a shout...  the atu was next to the analser on the bench still turned on but not connected to anything..  
iv noticed these faults now.  

any suggestions as to whats gone on???

billy uk
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K6AER
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Posts: 3512




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« Reply #1 on: February 03, 2008, 12:35:36 PM »

Send it to MFJ. Mine had the same problem. The mixer is bad and the repair will cost about $80 not including shipping. This was several years ago.
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M0JHA
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Posts: 646




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« Reply #2 on: February 03, 2008, 12:37:43 PM »

just noticed that this happens up to 14mhz.. above this the R shows 2 or 3 and the X symbol appears and shows  0  all the way up to 170mhz..

billy
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W4DL
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Posts: 182




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« Reply #3 on: February 03, 2008, 02:59:30 PM »

Throw it in the ocean and buy some real test gear.
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K7PEH
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« Reply #4 on: February 03, 2008, 03:36:13 PM »

>>>Throw it in the ocean and buy some real test gear.


What do you suggest as an alternative?
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AC5E
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Posts: 3585




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« Reply #5 on: February 03, 2008, 04:53:37 PM »

Well, I have a pair of Autek's, an AEA, and the General Radio bridge that was my go to when I was a lot younger and spryer. Maybe the VNA I intend to add to the arsenal when I get a place to put something else will change my mind, but the antenna analyzer I reach for first is still the MFJ 259b.

I hope yours is still in warranty, Billy.

73  Pete Allen  AC5E

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K4JSR
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Posts: 513




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« Reply #6 on: February 03, 2008, 05:19:06 PM »

Since I cannot afford an Agilent 8510 for my shack I will just have to make my 259-B do for now.
Like Pete said Billy, "I hope yours is still in warranty."
Good luck and 73,  Cal  K4JSR
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KE4DRN
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« Reply #7 on: February 03, 2008, 06:27:18 PM »

hi,

the 259b is a good tool for the price point it was designed for,
what do you use ?

73 james
...........
Throw it in the ocean and buy some real test gear.
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M0JHA
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Posts: 646




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« Reply #8 on: February 04, 2008, 01:20:08 AM »

i thought it was real test gear??  its a piece of equipment and it tests things.. doesnt this make it a piece of real test gear??? if by that you meant spend some silly amount of money on something that does the same thing albeit more accuretly .. no thanks ill save the difference to spend on the kids..

cheers for the replies. the "test gear" isnt under any warranty i got it second hand for £90 ..  so even if its not worth fixing its still been  the most used and most handy  piece of kit iv purchased to date and mfj will be selling another one..

i wonder if maybe the analyser has picked up stray rf from the antenna tuner and  destroyed something as it was still turned on when i tx on radio and they were next to each other..?

billy

 
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W8JI
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« Reply #9 on: February 04, 2008, 03:21:13 AM »

Sounds like you popped a diode in the bridge.

That comes from applying a good bit of external voltage. Perhaps you accidentally had RF applied to it somehow. The unwanted RF or voltage has to be through the antenna measurement port, and it has to be a wired connection. Laying next to the tuner won't do it.



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PD2R
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Posts: 131




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« Reply #10 on: February 04, 2008, 03:40:04 AM »

Billy,

If you have to buy a new analyzer you might want to check the following website: http://www.scarc.org.au/
Go to "Projects" and you will find a kit to built your own analyzer and you will be able to spend even more money on your kids, I believe money well spend ;-)
I do not own one of these myself but I know a some Dutch HAMs who have built these analyzer and are pleased with the result.

73, Maarten
 
       
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G8UBJ
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« Reply #11 on: February 04, 2008, 05:07:12 AM »

Okay, back up everyone. Have you changed the batteries or tried running it from an external 12v supply?

Next.. £90 was a bargain..ish, its out of warranty so if you have some time and the know how + a digital multi-meter I would open it up and test the bridge diodes..

http://www.dk3red.homepage.t-online.de/en/s8a.htm

I wouldn't propose fiddling without the correct calibration gear but here is some info on setting it up..

http://www.w8ji.com/mfj-259b_calibration.htm
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K5LXP
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« Reply #12 on: February 04, 2008, 06:09:45 AM »

It is not a big deal to replace the diodes, if that's the problem, and do W8JI's calibration routine.  I made a set of loads out of 1% 0805 resistors and PL-259's for calibrating my own, it's a cheap investment to have confidence in the accuracy of the unit.

Mark K5LXP
Albuquerque, NM
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K0BG
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« Reply #13 on: February 04, 2008, 06:24:46 AM »

Here's a suggestion for the future. Make up a PL259 with a dead short, and keep it screwed on to the 259 when you're not using it. As Tom alluded to, it is much easier to poof the diode than most folks realize.

Alan, KØBG
www.k0bg.com
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N3OX
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« Reply #14 on: February 04, 2008, 06:27:55 AM »

I agree with Mark.  That's what I did after one winter day when I walked over and touched a wire connected to the center pin of the SO-239 of my MFJ-259B.

POP!  One thing if it's a doorknob...

Anyway, mine was long out of warranty.  I ordered some diodes, Avago HSMS-2820 surface mount in a SOT-23 package and swapped them out and then did the calibration routine.

Hour or so of work and it works fine.  The diodes were 34 cents apiece from Arrow Electronics (www.arrownac.com)

Not sure that Arrow Northern Europe has an online store like Arrow North America... but you can dig around on that.

73
Dan




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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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