Hi
I have the MFJ 989C, and I am noticing that I can tune antenna to low SWR
but I also have noticed that the SWR often was jumping or spiking and very
unusual. I thought it may be coax or antenna or a short but then I noticed
also that the inductance coil is very sensitive. If you touch it or tap it
this will cause the SWR to spike. Also when it spikes, if you put a little
pressure on the Inductance coil knob it will solve the problem. Anyone else
have situation such as this? What did you do to fix the problem? I opened it
up and cleaned the contacts where I thought the problem was but still didn't
correct the problem.
Any ideas ???

" Tuuk" wrote in message
...
Hi
I have the MFJ 989C, and I am noticing that I can tune antenna to low SWR
but I also have noticed that the SWR often was jumping or spiking and very
unusual. I thought it may be coax or antenna or a short but then I noticed
also that the inductance coil is very sensitive. If you touch it or tap it
this will cause the SWR to spike. Also when it spikes, if you put a little
pressure on the Inductance coil knob it will solve the problem. Anyone
else
have situation such as this? What did you do to fix the problem? I opened
it
up and cleaned the contacts where I thought the problem was but still
didn't
correct the problem.
Any ideas ???



1. Check the contacts that you _don't_ think are the problem. Just because
it's a roller inductor doesn't mean that you're not the victim of a
garden-variety cold solder joint or a loose rivet. I'd check the whole
current path from one solder joint to the other (including the other moving
contacts -- there's a slip-ring _and_ a roller, yes?).

1a. You might want to try measuring resistance while you wiggle the thing
to see where the problem is. This can be difficult and frustrating, but if
you manage it you'll know for sure where the problem is.

2. _Only_ after you've verified that it isn't something else, see if you
can increase the contact pressure on the questionable joint. I'd think long
and hard before I did this on my own equipment, because it'll make it wear
out quicker.

" Tuuk" wrote in message
...
Hi
I have the MFJ 989C, and I am noticing that I can tune antenna to low SWR
but I also have noticed that the SWR often was jumping or spiking and very
unusual. I thought it may be coax or antenna or a short but then I noticed
also that the inductance coil is very sensitive. If you touch it or tap it
this will cause the SWR to spike. Also when it spikes, if you put a little
pressure on the Inductance coil knob it will solve the problem. Anyone
else
have situation such as this? What did you do to fix the problem? I opened
it
up and cleaned the contacts where I thought the problem was but still
didn't
correct the problem.
Any ideas ???



1. Check the contacts that you _don't_ think are the problem. Just because
it's a roller inductor doesn't mean that you're not the victim of a
garden-variety cold solder joint or a loose rivet. I'd check the whole
current path from one solder joint to the other (including the other moving
contacts -- there's a slip-ring _and_ a roller, yes?).

1a. You might want to try measuring resistance while you wiggle the thing
to see where the problem is. This can be difficult and frustrating, but if
you manage it you'll know for sure where the problem is.

2. _Only_ after you've verified that it isn't something else, see if you
can increase the contact pressure on the questionable joint. I'd think long
and hard before I did this on my own equipment, because it'll make it wear
out quicker.

I have the MFJ 989C, and I am noticing that I can tune antenna to low SWR
but I also have noticed that the SWR often was jumping or spiking and very
unusual. I thought it may be coax or antenna or a short but then I noticed
also that the inductance coil is very sensitive. If you touch it or tap it
this will cause the SWR to spike. Also when it spikes, if you put a little
pressure on the Inductance coil knob it will solve the problem. Anyone else
have situation such as this? What did you do to fix the problem? I opened it
up and cleaned the contacts where I thought the problem was but still didn't
correct the problem.

I had a problem similar to this with a tuner I bought from a guy at a
fleamarket some time ago - a homebrew SPC based on the design in the
ARRL handbook of a few years ago. The tuner was worse off than your
MFJ - it was jumpy during transmission, _and_ very difficult to get to
tune to a low SWR at all.

The problem turned out to be the roller inductor, which (like most of
the other parts he'd used) had been recycled from older equipment. It
turned out to have two sets of problems:

- The contacts at the end of the main roller were badly gunked up, with
dirt and with some form of old lubricant. There was a similar
amount of gunk in the bearing area where the contact wheel slides
back and forth on its support rod.

- There was a significant amount of pitting on both the contact wheel,
and on several sections of the wire on the inductor. I suspect that
the previous owner of this inductor had overstressed it, causing
arcing which pitted the contact area.

Fortunately, I was able to fix it completely with a bit of effort.

I started out by cleaning all of the dust and dirt off of the roller
inductor, using a combination of isopropyl alcohol, and some Caig
DeOxIt spray, and wiping with a clean cloth. I also cleaned the
contacts at the end of the roller, spraying with DeOxIt and then using
cloth to soak up the gunk which had been flushed out by the spray. I
repeated this process until all of the contact areas had been flushed
out, and no longer emitted any amount of black goo when sprayed.
Finally, the contact wheel's central bearing (where it slides/rolls
back and forth on a metal rod) needed to be flushed out in the same
way.

Fixing the pitting on the roller contact wheel and the wire was the
next task. The wheel was easy - it's solid silver, and I was able to
burnish it and restore a flat contact surface with a small riffler
file. I used the same approach to buff off the pitting on the roller
wire, but in doing so the silver plating on the polished areas was
removed and the underlying copper was exposed. I could have left it
that way, and just cleaned the wire more often to avoid oxidation, but
instead I decided to buy a small silverplating kit (from
www.caswellplating.com) and re-plate the wire. Doing so took only a
few minutes once I had the kit.

I finished up by giving the wire another cleaning with isopropyl, and
then sprayed a small amount of DeOxIt on a clean cotton cloth and
wiped down the wire, the roller contact surface, and the metal rod on
which the roller slides back and forth. This left all of the
electrical-contact surfaces clean, lubricated, and with a thin film of
antioxidant protection.

The results were everything I could have hoped for. The "jumpiness"
of the roller inductor is completely gone. Once tuned to a low SWR,
the SWR stays low during transmission. Fine adjustment of the
inductor control result in an easy, smooth change in SWR / reflected
power.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

I have the MFJ 989C, and I am noticing that I can tune antenna to low SWR
but I also have noticed that the SWR often was jumping or spiking and very
unusual. I thought it may be coax or antenna or a short but then I noticed
also that the inductance coil is very sensitive. If you touch it or tap it
this will cause the SWR to spike. Also when it spikes, if you put a little
pressure on the Inductance coil knob it will solve the problem. Anyone else
have situation such as this? What did you do to fix the problem? I opened it
up and cleaned the contacts where I thought the problem was but still didn't
correct the problem.

I had a problem similar to this with a tuner I bought from a guy at a
fleamarket some time ago - a homebrew SPC based on the design in the
ARRL handbook of a few years ago. The tuner was worse off than your
MFJ - it was jumpy during transmission, _and_ very difficult to get to
tune to a low SWR at all.

The problem turned out to be the roller inductor, which (like most of
the other parts he'd used) had been recycled from older equipment. It
turned out to have two sets of problems:

- The contacts at the end of the main roller were badly gunked up, with
dirt and with some form of old lubricant. There was a similar
amount of gunk in the bearing area where the contact wheel slides
back and forth on its support rod.

- There was a significant amount of pitting on both the contact wheel,
and on several sections of the wire on the inductor. I suspect that
the previous owner of this inductor had overstressed it, causing
arcing which pitted the contact area.

Fortunately, I was able to fix it completely with a bit of effort.

I started out by cleaning all of the dust and dirt off of the roller
inductor, using a combination of isopropyl alcohol, and some Caig
DeOxIt spray, and wiping with a clean cloth. I also cleaned the
contacts at the end of the roller, spraying with DeOxIt and then using
cloth to soak up the gunk which had been flushed out by the spray. I
repeated this process until all of the contact areas had been flushed
out, and no longer emitted any amount of black goo when sprayed.
Finally, the contact wheel's central bearing (where it slides/rolls
back and forth on a metal rod) needed to be flushed out in the same
way.

Fixing the pitting on the roller contact wheel and the wire was the
next task. The wheel was easy - it's solid silver, and I was able to
burnish it and restore a flat contact surface with a small riffler
file. I used the same approach to buff off the pitting on the roller
wire, but in doing so the silver plating on the polished areas was
removed and the underlying copper was exposed. I could have left it
that way, and just cleaned the wire more often to avoid oxidation, but
instead I decided to buy a small silverplating kit (from
www.caswellplating.com) and re-plate the wire. Doing so took only a
few minutes once I had the kit.

I finished up by giving the wire another cleaning with isopropyl, and
then sprayed a small amount of DeOxIt on a clean cotton cloth and
wiped down the wire, the roller contact surface, and the metal rod on
which the roller slides back and forth. This left all of the
electrical-contact surfaces clean, lubricated, and with a thin film of
antioxidant protection.

The results were everything I could have hoped for. The "jumpiness"
of the roller inductor is completely gone. Once tuned to a low SWR,
the SWR stays low during transmission. Fine adjustment of the
inductor control result in an easy, smooth change in SWR / reflected
power.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
. . .
As to RF coming out with the cover off - I've always heard that a
well-designed-and-constructed tuner will not radiate a significant
amount of RF even if the case is not a shielded one. Cebik, for
example, writes that "Well-wired ATUs do not radiate, consisting of
passive components only, so a metal case is not required" and
constructed an L-C-L tuner with a case made out of plexiglass.
. . .

I guess we each have our own definition of "significant". Get a small
fluorescent tube. Hold it near one end and wave the other near the tuner
coil. Depending on your power level, tuner setting, and antenna
impedance, the result might spur you to think about the meaning of
"significant".

Roy Lewallen, W7EL

Dave Platt wrote:
. . .
As to RF coming out with the cover off - I've always heard that a
well-designed-and-constructed tuner will not radiate a significant
amount of RF even if the case is not a shielded one. Cebik, for
example, writes that "Well-wired ATUs do not radiate, consisting of
passive components only, so a metal case is not required" and
constructed an L-C-L tuner with a case made out of plexiglass.
. . .

I guess we each have our own definition of "significant". Get a small
fluorescent tube. Hold it near one end and wave the other near the tuner
coil. Depending on your power level, tuner setting, and antenna
impedance, the result might spur you to think about the meaning of
"significant".

Roy Lewallen, W7EL