MFJ SWR Meter not at zero unplugged?

[archjeb]

Folks,

I have an MFJ VHF/UHF SWR/Watt Meter (MFJ-842). Lately the forward and reflect needle has not been at zero when its unplugged. Haven't dropped it or anything. Is this a known issue? Any way to correct?

Thanks,

-J

 

[Captain Kilowatt]

Static can cause the meters to be off the zero. You can tell this by waving a dry hand over the meter face. If the needle moves spray the meter face with Windex and wipe. If this is not the cause then check the zero set adjustment on the meter face. A little goes a long way so be gentle if you have to adjust it and DO NOT TURN IT TOO FAR.

 

[wavrider]

adjust meter zero by the front screw maybe

 

[Road Squawker]

well,all I will say is, that even on E-ham,(where almost every piece of equipment gets rave reviews), the 842 got bad grades,.... and the comments were worse.

https://www.google.com/url?sa=t&rct...l/7269&usg=AFQjCNH_uKvkmGxHaie-Mesu7XdxfxWuGQ

 

[bob85]

As CK says the meter can take on a static charge especially if you dust/wipe it with a dry cotton or similar cloth,
if its not a case of static charge & you need to adjust the needles, always back them down a little below zero then carefully wind them back up to zero.

 

[Captain Kilowatt]

I used to have a commercial FM transmitter that had static prone meters. Every time you went up there to take meter readings you had to spray the meter faces and wipe it clean otherwise you could get whatever you wanted (or REALLY didn't want LOL) for a reading just by waving your hand across the meter faces.

 

[archjeb]

Thanks for the pointers. It looks like it was indeed mostly static. I did spray it down with Windex and wiped, and that seemed to help a lot. I still could tweak the needles back down to zero a bit; but it looks like the front face is not easily accessible. I took the back cover off and it looks like the front section that holds the clear glass/frame to the needle assembly is glued.

Any idea of how to get to the front of the meter?

thanks.

-J

 

[Captain Kilowatt]

Is there not a small screw on the front bottom where the needle pivots from or is it behind the meter face?

Oh crap......I just Googled that meter. I see your problem. The adjustment points are behind the meter case. not a good design at all. You will need to pop the case apart to do that so unless it is WAY off I would leave it since the accuracy will not be off by more than a hair anyway. that is unless you are comfortable with tearing it apart.

 

[archjeb]

Is there not a small screw on the front bottom where the needle pivots from or is it behind the meter face?

Oh crap......I just Googled that meter. I see your problem. The adjustment points are behind the meter case. not a good design at all. You will need to pop the case apart to do that so unless it is WAY off I would leave it since the accuracy will not be off by more than a hair anyway. that is unless you are comfortable with tearing it apart.

Its not that bad. When I took the back cover off to inspect, its in 3 pieces and the front portion is glued; so you have to try and pry the adhesive loose to get to the front needle assembly. Its a crappy design...but it is what it is.

Thanks for the pointers. At least the needles are not floating like they were

-J

 

[Road Squawker]

...oh crap......I just Googled that meter. I see your problem....

not to mention the fact that MFJ manual information doesn't match the meter.

the manual states it is a 15/150 watt meter depending on the switch setting,........ the actual meter movement shown in the MFJ manual is 300/3000 watts.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwiN0d_9go7LAhUlvYMKHciGCTEQFggoMAI&url=http://www.ges.cz/sheets/m/mfj-842.pdf&usg=AFQjCNFRHHvc9JRRlqiNy-gW9CdmFLVhcQ


also, using the calibrating procedure in the manual, only the meters HIGH end points are "calibrated". it seems that the low needle settings should "float"