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Old November 8th 15, 03:25 AM posted to rec.radio.amateur.antenna
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Posts: 1,336
Default MFJ-269 repair (I win)

I just repaired an old MFJ-269 antenna analyzer. This time, the 4
diodes around the RF connector were NOT blown. Instead, it was crappy
SMT soldering for the components surrounding the diodes. The solder
joints looked ok before I resoldered them, but were obviously a bad
connection because several resistors just fell off the board when I
touched one end with the soldering iron, indicating the other end was
not properly soldered. With the resistor removed, the PCB pad looked
like it had never been soldered. If you don't have good soldering
tools, a steady hand, and a good microscope, DON'T try this as you'll
probably make a mess, as I did before I realized what was happening.

Because the various parts on the RF board were not originally making
good contact to the PCB pads, the calibration is off. The display
reads about 12% too high for impedance and dead on for reactance. I'm
debating if it's worth calibrating.
http://www.w8ji.com/mfj-259b_calibration.htm

Now working on an MFJ-259A, which looks like the usual blown diode
problem:
http://802.11junk.com/jeffl/MFJ-269-repair/

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old November 9th 15, 06:18 PM posted to rec.radio.amateur.antenna
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Posts: 154
Default MFJ-269 repair (I win)

On 11/7/2015 8:25 PM, Jeff Liebermann wrote:
I just repaired an old MFJ-269 antenna analyzer. This time, the 4
diodes around the RF connector were NOT blown. Instead, it was crappy
SMT soldering for the components surrounding the diodes. The solder
joints looked ok before I resoldered them, but were obviously a bad
connection because several resistors just fell off the board when I
touched one end with the soldering iron, indicating the other end was
not properly soldered. With the resistor removed, the PCB pad looked
like it had never been soldered. If you don't have good soldering
tools, a steady hand, and a good microscope, DON'T try this as you'll
probably make a mess, as I did before I realized what was happening.

Because the various parts on the RF board were not originally making
good contact to the PCB pads, the calibration is off. The display
reads about 12% too high for impedance and dead on for reactance. I'm
debating if it's worth calibrating.
http://www.w8ji.com/mfj-259b_calibration.htm

Now working on an MFJ-259A, which looks like the usual blown diode
problem:
http://802.11junk.com/jeffl/MFJ-269-repair/


That's how I got my MFJ-259B, about 15 years ago, Someone at the local
ham club had a defective one, gave it to a fellow ham to fix, he
returned it saying that he couldn't fix it.
I told the owner, let me have a shot at it, if I can fix it I'll
buy it from you. It was "the usual blown diode problem:" I shocked the
owner when I gave him $60.00 for the repaired unit. I don't think he
expected me to contact him again.
Mikek
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Old November 9th 15, 06:34 PM posted to rec.radio.amateur.antenna
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Posts: 3
Default MFJ-269 repair (I win)

On 11/9/2015 11:18 AM, amdx wrote:
On 11/7/2015 8:25 PM, Jeff Liebermann wrote:
I just repaired an old MFJ-269 antenna analyzer. This time, the 4
diodes around the RF connector were NOT blown. Instead, it was crappy
SMT soldering for the components surrounding the diodes. The solder
joints looked ok before I resoldered them, but were obviously a bad
connection because several resistors just fell off the board when I
touched one end with the soldering iron, indicating the other end was
not properly soldered. With the resistor removed, the PCB pad looked
like it had never been soldered. If you don't have good soldering
tools, a steady hand, and a good microscope, DON'T try this as you'll
probably make a mess, as I did before I realized what was happening.

Because the various parts on the RF board were not originally making
good contact to the PCB pads, the calibration is off. The display
reads about 12% too high for impedance and dead on for reactance. I'm
debating if it's worth calibrating.
http://www.w8ji.com/mfj-259b_calibration.htm

Now working on an MFJ-259A, which looks like the usual blown diode
problem:
http://802.11junk.com/jeffl/MFJ-269-repair/


That's how I got my MFJ-259B, about 15 years ago, Someone at the local
ham club had a defective one, gave it to a fellow ham to fix, he
returned it saying that he couldn't fix it.
I told the owner, let me have a shot at it, if I can fix it I'll
buy it from you. It was "the usual blown diode problem:" I shocked the
owner when I gave him $60.00 for the repaired unit. I don't think he
expected me to contact him again.
Mikek


Good for you Mike,

I once came across an Ameritron ALS-600 with analogue power supply and a
couple of vhf-uhf transceivers in a junk box at a garage sale. I asked
how much for the whole box. I was told 60 bucks. I assumed the stuff was
probably defective. However, the person selling it was a woman who had
lost her ham husband.

I wrote her a check for $500. That is what I figured a defective ALS-600
might be worth. She was shocked. I did not do this to be generous. I did
it because I knew that if I really screwed her on that deal, I would
feel guilty every time I used that amplifier. It turned out that the
amplifier actually worked but introduced a bit of distortion. I sent it
to MFJ and they rebalanced the output transistors. It has very good
fidelity now. The trip to MFJ cost about 200 dollars. I had to buy one
of their shipping boxes. Those are not cheap. Still, 700 dollars for an
ALS-600 is a bargain.

I liked that design so well that I bought an ALS-1300 which is just two
ALS-600s in a box. So, I have the 600 as a backup amp. That 1300 has
been such a good work horse. Tom at MFJ and others who worked on that
amp design did a fine job. Originally there was a defect in the
switching supply that they bought for it. Mine has been updated to
protect the 12 volt supply.
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Old November 9th 15, 08:07 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Dec 2014
Posts: 67
Default MFJ-269 repair (I win)

In article ,
Jeff Liebermann wrote:

Now working on an MFJ-259A, which looks like the usual blown diode
problem:
http://802.11junk.com/jeffl/MFJ-269-repair/


"Of course, when I got it back together (for the 2nd time), I found
the reading to be erratic and intermittent. It took a while to
discover that the owner had somehow spread the gold center contact
leafs in the type-N connector and my adapter wasn't making
contact."


My repeater cohort and I have seen quite a few N connectors which were
damaged in precisely this fashion.

One cause: some N-connector adapters floating around out there have
center pins which are either too large in diameter, improperly
tapered, or which protrude too far "forwards". I suspect that male N
connectors, if improperly installed, can have the same problem (the
pin is pushed too far into the connector).

In either case, (over)tightening such an N-male connector onto an
N-female will cause it to make excellent contact... once... as the pin
splays the female connector's contacts outwards. Subsequent
connection attempts with a properly-configured N male won't make good
contact.

In a pinch, you can try pinching the contact fingers back in, but it's
nigh-on impossible to restore them properly. Better to remove the
damaged female connector and replace it. Then, check all of your male
N connectors to make sure the center pin has the proper taper and is
in the proper position. A center pin with a rounded blunt end (rather
than a properly-tapered point) is Trouble.

This turned out to be all that was wrong with a defective TK-981 I
picked up at the De Anza ham flea market last year. Cut off the N
connector, solder-and-crimp a new one onto the pigtail, and it checks
out fine.

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Old November 9th 15, 08:20 PM posted to rec.radio.amateur.antenna
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Posts: 375
Default MFJ-269 repair (I win)

Dave Platt wrote:
One cause: some N-connector adapters floating around out there have
center pins which are either too large in diameter, improperly
tapered, or which protrude too far "forwards". I suspect that male N
connectors, if improperly installed, can have the same problem (the
pin is pushed too far into the connector).


With some types of cable, there is a tendency for the inner conductor
to "lengthen" relative to the outer shield when the cable is repeatedly
wound and unwound in a small radius.

This can sometimes push out the connector pin a little.


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Old November 9th 15, 08:25 PM posted to rec.radio.amateur.antenna
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Posts: 1,336
Default MFJ-269 repair (I win)

On Mon, 9 Nov 2015 11:18:20 -0600, amdx wrote:

That's how I got my MFJ-259B, about 15 years ago, Someone at the local
ham club had a defective one, gave it to a fellow ham to fix, he
returned it saying that he couldn't fix it.
I told the owner, let me have a shot at it, if I can fix it I'll
buy it from you. It was "the usual blown diode problem:" I shocked the
owner when I gave him $60.00 for the repaired unit. I don't think he
expected me to contact him again.
Mikek


Yep. I'm working on an MFJ-259B which might have blown diodes. It's
very easy to do. I'm considering adding a 1M resistor from the center
pin to ground to bleed off any static buildup. Beware of ungrounded
antennas. BTW, I paid $100 for mine. Grumble...

I'm also working with another ham that has an old MFJ-269 with some
very strange problems. I can't conjur a theory except that his has
the same problem as mine with the crappy soldering on the RF PCB. I've
recommended reflowing all the SMT parts around the coax connector.
That should either fix it, or destroy it.

Drivel: I'm trying to find a replacement LCD 1602 display with
backlighting. Plenty on eBay, but all the wrong size. Argh.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old November 9th 15, 08:31 PM posted to rec.radio.amateur.antenna
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Posts: 1,336
Default MFJ-269 repair (I win)

On Mon, 9 Nov 2015 11:07:16 -0800, (Dave
Platt) wrote:

In article ,
Jeff Liebermann wrote:

Now working on an MFJ-259A, which looks like the usual blown diode
problem:
http://802.11junk.com/jeffl/MFJ-269-repair/


"Of course, when I got it back together (for the 2nd time), I found
the reading to be erratic and intermittent. It took a while to
discover that the owner had somehow spread the gold center contact
leafs in the type-N connector and my adapter wasn't making
contact."


My repeater cohort and I have seen quite a few N connectors which were
damaged in precisely this fashion.


I can see that with N connectors that are assembled or crimped in
pieces, but not a 1 piece panel mount N receptacle. The PCB board
it's mounted upon would break before the connector.

One cause: some N-connector adapters floating around out there have
center pins which are either too large in diameter, improperly
tapered, or which protrude too far "forwards". I suspect that male N
connectors, if improperly installed, can have the same problem (the
pin is pushed too far into the connector).


Yep. However, I checked for that problem with some wire gauges.
Intermittent center pins, are a real problem, but not on this one.
Usually the center pin receptacle is ruined by a blob of solder on the
outside of the mating pin plug.

In either case, (over)tightening such an N-male connector onto an
N-female will cause it to make excellent contact... once... as the pin
splays the female connector's contacts outwards. Subsequent
connection attempts with a properly-configured N male won't make good
contact.


You should see the mess that problem produces when an unspecified
manufacturer of hard disk drives used power plugs that spread the
0.093 Molex connectors. Subsequent connections to "normal" size
0.093" connectors were very intermittent.

In a pinch, you can try pinching the contact fingers back in, but it's
nigh-on impossible to restore them properly. Better to remove the
damaged female connector and replace it. Then, check all of your male
N connectors to make sure the center pin has the proper taper and is
in the proper position. A center pin with a rounded blunt end (rather
than a properly-tapered point) is Trouble.

This turned out to be all that was wrong with a defective TK-981 I
picked up at the De Anza ham flea market last year. Cut off the N
connector, solder-and-crimp a new one onto the pigtail, and it checks
out fine.


Nicely done. I once saw a mobile (forgot the model) with the center
drilled out of the UHF SO-239, a pigtail inserted, and a BNC
receptacle at the end. I like it.




--
Jeff Liebermann

150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old November 9th 15, 09:19 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Sep 2012
Posts: 1,382
Default MFJ-269 repair (I win)

"Dave Platt" wrote in message
...
In article ,
Jeff Liebermann wrote:

Now working on an MFJ-259A, which looks like the usual blown diode
problem:
http://802.11junk.com/jeffl/MFJ-269-repair/


"Of course, when I got it back together (for the 2nd time), I found
the reading to be erratic and intermittent. It took a while to
discover that the owner had somehow spread the gold center contact
leafs in the type-N connector and my adapter wasn't making
contact."


My repeater cohort and I have seen quite a few N connectors which were
damaged in precisely this fashion.


The N connector is so-called because there are N different ways to assemble
it, and all of them wrong :-)


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Old November 12th 15, 07:20 PM posted to rec.radio.amateur.antenna
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Posts: 1
Default MFJ-269 repair (I win)

On 11/7/2015 8:25 PM, Jeff Liebermann wrote:
I just repaired an old MFJ-269 antenna analyzer. This time, the 4
diodes around the RF connector were NOT blown. Instead, it was crappy
SMT soldering for the components surrounding the diodes. The solder
joints looked ok before I resoldered them, but were obviously a bad
connection because several resistors just fell off the board when I
touched one end with the soldering iron, indicating the other end was
not properly soldered. With the resistor removed, the PCB pad looked
like it had never been soldered. If you don't have good soldering
tools, a steady hand, and a good microscope, DON'T try this as you'll
probably make a mess, as I did before I realized what was happening.

Because the various parts on the RF board were not originally making
good contact to the PCB pads, the calibration is off. The display
reads about 12% too high for impedance and dead on for reactance. I'm
debating if it's worth calibrating.
http://www.w8ji.com/mfj-259b_calibration.htm

Now working on an MFJ-259A, which looks like the usual blown diode
problem:
http://802.11junk.com/jeffl/MFJ-269-repair/

I've generally found MFJ stuff has decent design and rather good
components, but terrible wave soldering on the PC boards (and sometimes
hand soldering on components off the board like chassis mounted
connectors). On my 259B, it worked well for almost a year, and then
became erratic. When I saw how many soldered joints weren't, I decided
not to try to figure out which ones were bad: I just went around and
resoldered everything on the board. Since then it has worked perfectly.

Wave soldering is a marginal thing, I think it is amazing how many times
it does work. Think about how it goes: Basically the PC board is
suspended just above a vat of molten solder, and a wave is caused to run
across the vat. The wave, we hope, just reaches up to the connections on
the board and solders them. Too high and it makes solder bridges. Too
low and it either misses connections or at least does not stay on them
long enough. And it is not long on a connection at best, so does it get
it hot enough?

It is not just fairly inexpensive things like my MFJ analyzer that have
had problems. I did the "resolder the whole board" thing on my Phase
Linear preamp many years ago also, and that was by no means low end!

Bob Wilson
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Old November 12th 15, 10:11 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Jul 2006
Posts: 220
Default MFJ-269 repair (I win)

I have a number of MFJ items that I picked up in non-working
conditions and fixed up. They include MFJ-259B, MFJ-931, MFJ-949E
and others. Other than the 259B which involved cleaning leaky battery
residue and replacing the input diodes. most of the work involved
resoldering and/or replacing blown meters, and in once case
a bandswitch. Once repaired, everything
has remained totally reliable and functional. I've never had
problems ordering parts from them to fix the stuff.
The 'Mighty Fine Junk' reputation is deserved only because of
the poor soldering, but once repaired it serves one well -- at
least in my books!

Irv VE6BP



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