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 MFJ-874 Power/ SWR Meter 
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Post MFJ-874 Power/ SWR Meter
Back in 2012, I bought the above from someone off this site, I didn't have an immediate use for it so it went into storage and hasn't seen the light of day until yesterday. I tried it on 2 meters and it seems to work, I then went to try it on HF and choose the 10 m band, and not a thing! This particularly meter has two sets of connections, one set for HR & 6 metres and the other set for VHF/UHF, and no I haven't connected them wrong.

Could it be a dry joint fault? I have heard people fixing SWR/Power meters so I am hoping it isn't impossible to fix cheaply!


Sun Jul 05, 2020 6:17 pm
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
2E0CPX wrote:
Back in 2012, I bought the above from someone off this site, I didn't have an immediate use for it so it went into storage and hasn't seen the light of day until yesterday. I tried it on 2 meters and it seems to work, I then went to try it on HF and choose the 10 m band, and not a thing! This particularly meter has two sets of connections, one set for HR & 6 metres and the other set for VHF/UHF, and no I haven't connected them wrong.

Could it be a dry joint fault? I have heard people fixing SWR/Power meters so I am hoping it isn't impossible to fix cheaply!

Having worked in an emporium in the past, and encountered this issue before, this may seem like a really daft question, but did you put the radio on to AM, FM, or CW when you did the test on 10m?

Some folks forget, and have their rigs set on SSB, which of course, with no audio gives no carrier.

Like I say,just a thought...


73, Mark... :wave:

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Mon Jul 06, 2020 6:46 am
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
Another thought was does the transceiver have multiple antenna sockets, say one for UHF, one VHF, one for HF?

Also, does the rig allow switching between antenna outputs, I.E. ant-1 ant-2?

Does the rig have a transverter setting?

Is the rig actually producing any output power? (does its own indication system show output?).

The thing that struck me about your statement was that when you purchased the unit you don't say whether you actually tested it at the time, if not then maybe the issue was there at the start.

Is there ANY indication on the MFJ on either forward or reflected ranges on HF?

73...

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Mon Jul 06, 2020 10:51 am
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
G0KZZ wrote:
2E0CPX wrote:
Back in 2012, I bought the above from someone off this site, I didn't have an immediate use for it so it went into storage and hasn't seen the light of day until yesterday. I tried it on 2 meters and it seems to work, I then went to try it on HF and choose the 10 m band, and not a thing! This particularly meter has two sets of connections, one set for HR & 6 metres and the other set for VHF/UHF, and no I haven't connected them wrong.

Could it be a dry joint fault? I have heard people fixing SWR/Power meters so I am hoping it isn't impossible to fix cheaply!

Having worked in an emporium in the past, and encountered this issue before, this may seem like a really daft question, but did you put the radio on to AM, FM, or CW when you did the test on 10m?

Some folks forget, and have their rigs set on SSB, which of course, with no audio gives no carrier.

Like I say,just a thought...


73, Mark... :wave:


I tried it on 10 m FM and absolutely nothing


Mon Jul 06, 2020 1:48 pm
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
G0KZZ wrote:
Another thought was does the transceiver have multiple antenna sockets, say one for UHF, one VHF, one for HF?

Also, does the rig allow switching between antenna outputs, I.E. ant-1 ant-2?

Does the rig have a transverter setting?

Is the rig actually producing any output power? (does its own indication system show output?).

The thing that struck me about your statement was that when you purchased the unit you don't say whether you actually tested it at the time, if not then maybe the issue was there at the start.

Is there ANY indication on the MFJ on either forward or reflected ranges on HF?

73...


I'm using an FT-818, there is no switch on the back on the MFJ, which I notice there is on a cheaper Chinese copy which is on the market. Wasn't tested at the time of purchase, I was going to take it down to the local ARS, but that never happened and I got into DMR and DStar so never bothered about getting an HF rig until recently.


Mon Jul 06, 2020 1:53 pm
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
2E0CPX wrote:
I'm using an FT-818, there is no switch on the back on the MFJ, which I notice there is on a cheaper Chinese copy which is on the market. Wasn't tested at the time of purchase, I was going to take it down to the local ARS, but that never happened and I got into DMR and DStar so never bothered about getting an HF rig until recently.

That MFJ-874 looks identical to a NISSEI RS-502.

OK, another crazy idea. I see that there is a push button switch next to the SWR set knob that needs to be in for VHF/UHF, and out for HF. Have you switched that over?

Also, if you've had the unit stored for eight years it could be that the switch has oxidised a little. Try operating the switch 10 - 20 times and see if it works then. If it does then work but is perhaps a bit 'jumpy', maybe a bit of contact cleaner or WD40 will bring it back to life.

To be continued... :D

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Mon Jul 06, 2020 6:51 pm
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
Could it be that there is nothing wrong with the meter and the radio isnt producing rf?
ie: the radio has a faulty hf rf circuit.

Just a thought....

Mark

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Tue Jul 07, 2020 9:11 am
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
M1MPW wrote:
Could it be that there is nothing wrong with the meter and the radio isnt producing rf?
ie: the radio has a faulty hf rf circuit.

Just a thought....

Mark


G0KZZ Posted: Mon Jul 06, 2020 10:51 am wrote:
...Is the rig actually producing any output power? (does its own indication system show output?)...

:rolleyes:

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Tue Jul 07, 2020 10:23 am
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
I suppose a good test would be connect a dummy load , key down, and see if the load warms up!

Oh, yes I missed the line by KZZ....

Mark

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Tue Jul 07, 2020 10:57 am
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
G0KZZ wrote:
2E0CPX wrote:
I'm using an FT-818, there is no switch on the back on the MFJ, which I notice there is on a cheaper Chinese copy which is on the market. Wasn't tested at the time of purchase, I was going to take it down to the local ARS, but that never happened and I got into DMR and DStar so never bothered about getting an HF rig until recently.

That MFJ-874 looks identical to a NISSEI RS-502.

OK, another crazy idea. I see that there is a push-button switch next to the SWR set knob that needs to be in for VHF/UHF, and out for HF. Have you switched that over?

Also, if you've had the unit stored for eight years it could be that the switch has oxidised a little. Try operating the switch 10 - 20 times and see if it works then. If it does then work but is perhaps a bit 'jumpy', maybe a bit of contact cleaner or WD40 will bring it back to life.

To be continued... :D


Yes I have set that button properly and yes the rig generates rf, I haven't opened it up, last time I looked inside an SWR meter there wasn't much to it!


Mon Jul 13, 2020 12:30 pm
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
I've opened it up, everything seems to be there.


Tue Jul 14, 2020 11:04 am
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
With all else working OK that would ultimately point to the diodes in the coupler itself being faulty.

Sometimes the sensing lines are open and you can get to the diodes fairly easily, others are hidden away inside a shielding box, and if you are really unlucky the box will have soldered joints.

As the meter has two seperate pairs of connecting sockets I would guess they have gone for two seperately shielded couplers.

You will have to open up the one for the range that is not working and see if you can identify the diodes used. If you are lucky they will have some kind of marking that will help identify what they are, if not you will need to try a substitute set of suitable diodes.

Also, once the diodes have been replaced you might need to rebalance the coupler, and almost definitely recalibrate the power readings.

It sounds a bit daunting but in reality it just involves resetting a few preset potentiometers generally speaking, sometimes you may also find a trimmer capacitor too, it all depends on the design used.

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Fri Jul 17, 2020 10:47 am
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 MFJ-874 Power/ SWR Meter 
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Post Re: MFJ-874 Power/ SWR Meter
G0KZZ wrote:
With all else working OK that would ultimately point to the diodes in the coupler itself being faulty.

Sometimes the sensing lines are open and you can get to the diodes fairly easily, others are hidden away inside a shielding box, and if you are really unlucky the box will have soldered joints.

As the meter has two seperate pairs of connecting sockets I would guess they have gone for two seperately shielded couplers.

You will have to open up the one for the range that is not working and see if you can identify the diodes used. If you are lucky they will have some kind of marking that will help identify what they are, if not you will need to try a substitute set of suitable diodes.

Also, once the diodes have been replaced you might need to rebalance the coupler, and almost definitely recalibrate the power readings.

It sounds a bit daunting but in reality it just involves resetting a few preset potentiometers generally speaking, sometimes you may also find a trimmer capacitor too, it all depends on the design used.


Thanks


Fri Jul 31, 2020 2:56 pm
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