I have an old MFJ SWR meter with a built in counter. It has an LCD
display to read frequency and it uses a small 2 inch korean made
plastic analog meter to read SWR. I keep this unit in my service truck
wrapped up, however it may have gotten jarred because the unit still
works fine but all of a sudden mechanical zero is up about ten percent
of full scale.

There is no zero adjustment accessable through the front of the
instrument. This is a nice little unit however to adjust mechanical
zero you have remove the analog meter and open the case. This requires
complete disassembly of the entire instrument and it is a real pain.

I did this and opened the small meter and adjusted mechanical zero.
This is a simple procedure however the problem is static electricity.
Depending on how I hold this meter, touch it, rub my finger or even a
piece of cardboard near it, mechanical zero may shift. At times I
think that I have it zeroed and I close the case up only to find that
zero has shifted. Then I touch it wirth my finger and zero will
sometimes shift again.

So the problem is that I don't know if after I touch this thing if It
is totally discharged and it is really at zero or if static
electricity has influenced the position of the needle. This simple job
is really driving me nuts. It is very dry in the house and I'm sure
that this may have something to do with it, but I just don't know how
to compensate for this.

Obviously it is important that my adjustment is correct as there is no
access to it once the unit is re assembled. Can anyone offer any
advice? Thanks, Lenny.

On 2/18/2010 3:00 PM klem kedidelhopper spake thus:

So the problem is that I don't know if after I touch this thing if It
is totally discharged and it is really at zero or if static
electricity has influenced the position of the needle. This simple job
is really driving me nuts. It is very dry in the house and I'm sure
that this may have something to do with it, but I just don't know how
to compensate for this.

Obviously it is important that my adjustment is correct as there is no
access to it once the unit is re assembled. Can anyone offer any
advice?

I think you alluded to the answer yourself when you pointed out that the
house is very dry: take the meter to a more humid environment, which
should cut down on that annoying static electricity.


--
You were wrong, and I'm man enough to admit it.

- a Usenet "apology"

David Nebenzahl writes:

On 2/18/2010 3:00 PM klem kedidelhopper spake thus:

So the problem is that I don't know if after I touch this thing if It
is totally discharged and it is really at zero or if static
electricity has influenced the position of the needle. This simple job
is really driving me nuts. It is very dry in the house and I'm sure
that this may have something to do with it, but I just don't know how
to compensate for this.
Obviously it is important that my adjustment is correct as there is
no
access to it once the unit is re assembled. Can anyone offer any
advice?

I think you alluded to the answer yourself when you pointed out that
the house is very dry: take the meter to a more humid environment,
which should cut down on that annoying static electricity.

Wipe the face with an anti-cling dryer sheet.

--
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Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

On Thu, 18 Feb 2010 15:00:15 -0800 (PST), klem kedidelhopper
wrote:

I have an old MFJ SWR meter with a built in counter.

Which one of these?
http://www.mfjenterprises.com/Catergories.php?sec=13
The only one that has both an LCD and meter is the MFJ-259B:
http://www.mfjenterprises.com/Product.php?productid=MFJ-259B
Any particular reason why you find it necessary to hide the model
number? You generally get much better answers if you disclose such
information.

It has an LCD
display to read frequency and it uses a small 2 inch korean made
plastic analog meter to read SWR. I keep this unit in my service truck
wrapped up, however it may have gotten jarred because the unit still
works fine but all of a sudden mechanical zero is up about ten percent
of full scale.

See if you can find a similar meter. Note that the jeweled bearings
at the ends of the meter needle shaft are thin brass cantilevered
arrangements, which are easily bent by a high G shock load. It's not
unusual for the meter pivot point to literally fall out of the jeweled
bearing. More commonly, the arm gets bent, causing the meter to move
erratically. It's also possible to "tangle" the two springs that zero
the meter. That results in a zero drift, similar to what you're
seeing. Swing the meter back and forth sideways and see if the needle
moves smoothly.

There is no zero adjustment accessable through the front of the
instrument. This is a nice little unit however to adjust mechanical
zero you have remove the analog meter and open the case. This requires
complete disassembly of the entire instrument and it is a real pain.

Yep. MFJ probably saved about 5 cents on the cost of the case by
removing the meter adjust holes. However, meters should not require
zero adjustment unless affected by a nearby magnetic field. With two
meters that close together, there's going to be some magnetic
interaction. Perhaps MFJ adjusts it at the factory, and doesn't want
anyone changing it as the procedure might be a bit convoluted. Dunno
and I'm guessing.

That brings about another possibility that all the jarring around in
the service truck cause the meter magnet to break loose. Shake it.
Hear anything rattling?

I did this and opened the small meter and adjusted mechanical zero.
This is a simple procedure however the problem is static electricity.
Depending on how I hold this meter, touch it, rub my finger or even a
piece of cardboard near it, mechanical zero may shift. At times I
think that I have it zeroed and I close the case up only to find that
zero has shifted. Then I touch it wirth my finger and zero will
sometimes shift again.

So the problem is that I don't know if after I touch this thing if It
is totally discharged and it is really at zero or if static
electricity has influenced the position of the needle. This simple job
is really driving me nuts. It is very dry in the house and I'm sure
that this may have something to do with it, but I just don't know how
to compensate for this.

I don't think it's static electricity. If it were, BOTH meters would
be affected. Since you didn't mention that there were two meters or
that the other meter was affected, my guess is that only the SWR meter
is giving you problems. Also, the meter plastic front is not large
enough to collect a very large static charge.

Schematic:
http://www.dk3red.homepage.t-online.de/en/s8a.htm
Hmmm.... SWR meter has a 100K pot in series to the output of the OP
amp. Not exactly low impedance. So, the meter is essentially running
with no dampening. Eliminating static electricity and a broken shunt,
that leaves mechanical damage.

Obviously it is important that my adjustment is correct as there is no
access to it once the unit is re assembled. Can anyone offer any
advice? Thanks, Lenny.

No advice. Just two questions:
1. What's the model number?
2. Are both meters exhibiting the same zeroing problem?


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

klem kedidelhopper wrote in message
...
I have an old MFJ SWR meter with a built in counter. It has an LCD
display to read frequency and it uses a small 2 inch korean made
plastic analog meter to read SWR. I keep this unit in my service truck
wrapped up, however it may have gotten jarred because the unit still
works fine but all of a sudden mechanical zero is up about ten percent
of full scale.

There is no zero adjustment accessable through the front of the
instrument. This is a nice little unit however to adjust mechanical
zero you have remove the analog meter and open the case. This requires
complete disassembly of the entire instrument and it is a real pain.

I did this and opened the small meter and adjusted mechanical zero.
This is a simple procedure however the problem is static electricity.
Depending on how I hold this meter, touch it, rub my finger or even a
piece of cardboard near it, mechanical zero may shift. At times I
think that I have it zeroed and I close the case up only to find that
zero has shifted. Then I touch it wirth my finger and zero will
sometimes shift again.

So the problem is that I don't know if after I touch this thing if It
is totally discharged and it is really at zero or if static
electricity has influenced the position of the needle. This simple job
is really driving me nuts. It is very dry in the house and I'm sure
that this may have something to do with it, but I just don't know how
to compensate for this.

Obviously it is important that my adjustment is correct as there is no
access to it once the unit is re assembled. Can anyone offer any
advice? Thanks, Lenny.

Mask off the scale area, coil section ,bearings and hair spring, and bulb
section and spray all else inside and out with nickel spray? or paint with
real or faux aquadag (PVA and graphite). With painted-in conductive tails
inside and out to chassis


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm

klem kedidelhopper wrote in message
...
I have an old MFJ SWR meter with a built in counter. It has an LCD
display to read frequency and it uses a small 2 inch korean made
plastic analog meter to read SWR. I keep this unit in my service truck
wrapped up, however it may have gotten jarred because the unit still
works fine but all of a sudden mechanical zero is up about ten percent
of full scale.

There is no zero adjustment accessable through the front of the
instrument. This is a nice little unit however to adjust mechanical
zero you have remove the analog meter and open the case. This requires
complete disassembly of the entire instrument and it is a real pain.

I did this and opened the small meter and adjusted mechanical zero.
This is a simple procedure however the problem is static electricity.
Depending on how I hold this meter, touch it, rub my finger or even a
piece of cardboard near it, mechanical zero may shift. At times I
think that I have it zeroed and I close the case up only to find that
zero has shifted. Then I touch it wirth my finger and zero will
sometimes shift again.

So the problem is that I don't know if after I touch this thing if It
is totally discharged and it is really at zero or if static
electricity has influenced the position of the needle. This simple job
is really driving me nuts. It is very dry in the house and I'm sure
that this may have something to do with it, but I just don't know how
to compensate for this.

Obviously it is important that my adjustment is correct as there is no
access to it once the unit is re assembled. Can anyone offer any
advice? Thanks, Lenny.

Are you sure it is not erroneous electronics doing the sensing and actually
putting out some wavering DC instead of zero, rather than static
electricity. Monitoring terminals of meter with a DVM say

klem kedidelhopper schrieb:

[...]
So the problem is that I don't know if after I touch this thing if It
is totally discharged and it is really at zero or if static
electricity has influenced the position of the needle. This simple job
is really driving me nuts. It is very dry in the house and I'm sure
that this may have something to do with it, but I just don't know how
to compensate for this.

Obviously it is important that my adjustment is correct as there is no
access to it once the unit is re assembled. Can anyone offer any
advice? Thanks, Lenny.

Hi Lenny,

use something like this:

http://www.youtube.com/watch?v=l5_8lN_2aKs

HTH

Reinhard

On Fri, 19 Feb 2010 10:48:21 -0000, "N_Cook"
wrote:

Are you sure it is not erroneous electronics doing the sensing and actually
putting out some wavering DC instead of zero, rather than static
electricity. Monitoring terminals of meter with a DVM say

Getting to the meter terminals is a bit awkward but not impossible.
See photos at:
http://jan.kepic.cz/accessories/MFJ-259b/index.htm
http://fs.textcube.com/blog/0/281/attach/Xc2ili2zpJ.jpg

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Feb 19, 11:06*am, Jeff Liebermann wrote:
On Fri, 19 Feb 2010 10:48:21 -0000, "N_Cook"
wrote:

Are you sure it is not erroneous electronics doing the sensing and actually
putting out some wavering DC instead of zero, rather than static
electricity. Monitoring terminals of meter with a DVM say

Getting to the meter terminals is a bit awkward but not impossible.
See photos at:
http://jan.kepic.cz/accessories/MFJ-259b/index.htm
http://fs.textcube.com/blog/0/281/attach/Xc2ili2zpJ.jpg

--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558

It is static electricity. Try rubbing your friendly neighborhood cat
or dog and then put your hand on the meter face. I'd bet my pension
that you can move the needle from its normal zero point!

On Fri, 19 Feb 2010 19:20:06 -0800 (PST), "hr(bob) "
wrote:
It is static electricity. Try rubbing your friendly neighborhood cat
or dog and then put your hand on the meter face. I'd bet my pension
that you can move the needle from its normal zero point!

Well Ok. I'll concede that it might be static electricity. Currently,
the humidity here is between 75-100% depending on who's home wx
station I want to believe:
http://www.wunderground.com/US/CA/Santa_Cruz.html
I could rub the overly friendly cat or worthless dog until my hand
tires and still not get a spark. However, the author indicates that
his house is quite dry, but doesn't indicate if he's throwing
lightning bolts (a sure sign of static electricity). I've seen static
electricity affect meters, but only on larger panel meters. The
smaller meters don't seem to have enough insulating plastic to store a
big enough charge. I have a nearby friend that has an MFJ-259B and
will do some tinkering as time permits.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Feb 20, 11:35*am, Jeff Liebermann wrote:
On Fri, 19 Feb 2010 19:20:06 -0800 (PST), "hr(bob) "

wrote:
It is static electricity. *Try rubbing your friendly neighborhood cat
or dog and then put your hand on the meter face. *I'd bet my pension
that you can move the needle from its normal zero point!

Well Ok. *I'll concede that it might be static electricity. Currently,
the humidity here is between 75-100% depending on who's home wx
station I want to believe:
http://www.wunderground.com/US/CA/Santa_Cruz.html
I could rub the overly friendly cat or worthless dog until my hand
tires and still not get a spark. *However, the author indicates that
his house is quite dry, but doesn't indicate if he's throwing
lightning bolts (a sure sign of static electricity). *I've seen static
electricity affect meters, but only on larger panel meters. *The
smaller meters don't seem to have enough insulating plastic to store a
big enough charge. *I have a nearby friend that has an MFJ-259B and
will do some tinkering as time permits.

--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558

I can put my hand (here in the Chicago area) on the plastic face of my
multimeter, slide my index finger around in circles on the clear
plastic that is the faceplate of the meter, and get the no-input /
meter zero to go up or down 1/10 of the full-scale deflection. Of
course, it is about freezing and relative humidity is low enough that
when I slide out of my car I make sure to touch the car with my car
keys firmly grasped when I remember. Otherwise, I get a pretty good
shock.

On Feb 20, 10:32*pm, "hr(bob) "
wrote:
On Feb 20, 11:35*am, Jeff Liebermann wrote:



On Fri, 19 Feb 2010 19:20:06 -0800 (PST), "hr(bob) "

wrote:
It is static electricity. *Try rubbing your friendly neighborhood cat
or dog and then put your hand on the meter face. *I'd bet my pension
that you can move the needle from its normal zero point!

Well Ok. *I'll concede that it might be static electricity. Currently,
the humidity here is between 75-100% depending on who's home wx
station I want to believe:
http://www.wunderground.com/US/CA/Santa_Cruz.html
I could rub the overly friendly cat or worthless dog until my hand
tires and still not get a spark. *However, the author indicates that
his house is quite dry, but doesn't indicate if he's throwing
lightning bolts (a sure sign of static electricity). *I've seen static
electricity affect meters, but only on larger panel meters. *The
smaller meters don't seem to have enough insulating plastic to store a
big enough charge. *I have a nearby friend that has an MFJ-259B and
will do some tinkering as time permits.

--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558

I can put my hand (here in the Chicago area) on the plastic face of my
multimeter, slide my index finger around in circles on the clear
plastic that is the faceplate of the meter, and get the no-input /
meter zero to go up or down 1/10 of the full-scale deflection. *Of
course, it is about freezing and relative humidity is low enough that
when I slide out of my car I make sure to touch the car with my car
keys firmly grasped when I remember. *Otherwise, I get a pretty good
shock.

After setting zero I moved my finger over the meter face first thing
in the morning and the needle moved up scale about 10 percent. I let
it sit on the bench for about 24 hours without touching it. When I
looked at it again it was back to zero. So the trick is to set it,
leave it for a day let it discharge, and then tweak it again. Clumsy
procedure but it works. Glad this is my own equipment and not a
customer repair job....Lenny

On Thu, 25 Feb 2010 07:32:28 -0800 (PST), klem kedidelhopper
wrote:

After setting zero I moved my finger over the meter face first thing
in the morning and the needle moved up scale about 10 percent. I let
it sit on the bench for about 24 hours without touching it. When I
looked at it again it was back to zero. So the trick is to set it,
leave it for a day let it discharge, and then tweak it again. Clumsy
procedure but it works. Glad this is my own equipment and not a
customer repair job....Lenny

Nice workaround. So it is static. Is this NORMAL for a small panel
meter? We don't have much of a static problem on the left coast, so I
don't see much of that. I waved my hand around various small panel
meters around the shop. No deflection.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Feb 25, 2:20*pm, Jeff Liebermann wrote:
On Thu, 25 Feb 2010 07:32:28 -0800 (PST), klem kedidelhopper

wrote:
After setting zero I moved my finger over the meter face first thing
in the morning and the needle moved up scale about 10 percent. I let
it sit on the bench for about 24 hours without touching it. When I
looked at it again it was back to zero. So the trick is to set it,
leave it for a day let it discharge, and then tweak it again. Clumsy
procedure but it works. Glad this is my own equipment and not a
customer repair job....Lenny

Nice workaround. *So it is static. *Is this NORMAL for a small panel
meter? *We don't have much of a static problem on the left coast, so I
don't see much of that. *I waved my hand around various small panel
meters around the shop. *No deflection.

--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558

Well if it were Summer this would be a different story. It does get
pretty humid here in New Hampshire at times and I'm sure that during
those months static would pose no problem at all. During the Winter
the wood stove is going here constantly and it is very dry. We walk
around discharging ourselves on handrails, metal cabinets, doorknobs,
etc. I once wiped out the front end of a portable two way by walking
across a room holding it in my hand and carelessly touching the rubber
duck to ground. I did that only once....Lenny

Jeff Liebermann wrote:
On Thu, 25 Feb 2010 07:32:28 -0800 (PST), klem kedidelhopper
wrote:

After setting zero I moved my finger over the meter face first thing
in the morning and the needle moved up scale about 10 percent. I let
it sit on the bench for about 24 hours without touching it. When I
looked at it again it was back to zero. So the trick is to set it,
leave it for a day let it discharge, and then tweak it again. Clumsy
procedure but it works. Glad this is my own equipment and not a
customer repair job....Lenny

Nice workaround. So it is static. Is this NORMAL for a small panel
meter? We don't have much of a static problem on the left coast, so I
don't see much of that. I waved my hand around various small panel
meters around the shop. No deflection.

The easiest and best solution is to eliminate the static charge by rubbing
the meter face with a clothes dryer anti-cling sheet. Alternatively, buy a
bottle of anti-cling spray and give the meter a ligh misting.
That will dissipate the static charge and you can handle the meter as you
wish without upsetting the zero setting.

--
David
dgminala at mediacombb dot net

On Mar 17, 11:57*am, "Dave M" wrote:
Jeff Liebermann wrote:
On Thu, 25 Feb 2010 07:32:28 -0800 (PST), klem kedidelhopper
wrote:

After setting zero I moved my finger over the meter face first thing
in the morning and the needle moved up scale about 10 percent. I let
it sit on the bench for about 24 hours without touching it. When I
looked at it again it was back to zero. So the trick is to set it,
leave it for a day let it discharge, and then tweak it again. Clumsy
procedure but it works. Glad this is my own equipment and not a
customer repair job....Lenny

Nice workaround. *So it is static. *Is this NORMAL for a small panel
meter? *We don't have much of a static problem on the left coast, so I
don't see much of that. *I waved my hand around various small panel
meters around the shop. *No deflection.

The easiest and best solution is to eliminate the static charge by rubbing
the meter face with a clothes dryer anti-cling sheet. Alternatively, buy a
bottle of anti-cling spray and give the meter a ligh misting.
That will dissipate the static charge and you can handle the meter as you
wish without upsetting the zero setting.

--
David
dgminala at mediacombb dot net

This all sounds terribly bizarre - Its a moving coil meter, it might
go "whack" on getting a static charge, but a steady reading? - must be
an INCREDIBLY sensitive meter movement- femtoamps? - have a look at
the output of the op amp, preferably with an analogue meter - (as
suggested) (no signal, 0 output) and the bias resistors around it.
Especially the high value (100k ones) (any Tantalum capacitors,
replace them)
(sorry Dave - a view from the trenches)

Andrew VK3BFA.

PS - its axiomatic that the thing causing the fault is in the least
accessible section of the cct. A variation of Murphys Law.

On Tue, 27 Apr 2010 07:04:53 -0700 (PDT), Andrew VK3BFA
wrote:

On Mar 17, 11:57*am, "Dave M" wrote:
Jeff Liebermann wrote:
On Thu, 25 Feb 2010 07:32:28 -0800 (PST), klem kedidelhopper
wrote:

After setting zero I moved my finger over the meter face first thing
in the morning and the needle moved up scale about 10 percent. I let
it sit on the bench for about 24 hours without touching it. When I
looked at it again it was back to zero. So the trick is to set it,
leave it for a day let it discharge, and then tweak it again. Clumsy
procedure but it works. Glad this is my own equipment and not a
customer repair job....Lenny

Nice workaround. *So it is static. *Is this NORMAL for a small panel
meter? *We don't have much of a static problem on the left coast, so I
don't see much of that. *I waved my hand around various small panel
meters around the shop. *No deflection.

The easiest and best solution is to eliminate the static charge by rubbing
the meter face with a clothes dryer anti-cling sheet. Alternatively, buy a
bottle of anti-cling spray and give the meter a ligh misting.
That will dissipate the static charge and you can handle the meter as you
wish without upsetting the zero setting.

--
David
dgminala at mediacombb dot net

This all sounds terribly bizarre - Its a moving coil meter, it might
go "whack" on getting a static charge, but a steady reading?
It is NOT current flow from a static discharge that creates the
reading. It is a static (as in unchanging) charge on the case
attracting or repelling some other part of the movement.



- must be
an INCREDIBLY sensitive meter movement- femtoamps? - have a look at
the output of the op amp, preferably with an analogue meter - (as
suggested) (no signal, 0 output) and the bias resistors around it.
Especially the high value (100k ones) (any Tantalum capacitors,
replace them)
(sorry Dave - a view from the trenches)

Andrew VK3BFA.

PS - its axiomatic that the thing causing the fault is in the least
accessible section of the cct. A variation of Murphys Law.