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Author Topic: MFJ-993 Tuner Problem  (Read 206 times)

WB1ANA

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MFJ-993 Tuner Problem
« on: September 20, 2022, 06:10:09 PM »

I recently picked up a used MFJ-993 (not the B version) tuner as part of a package deal that came with a storage unit auction.  Condition was unknown, so I bought it caveat emptor.  It powers up fine and all diagnostics pass, including all of the relay checks, but the unit does not tune.  The frequency counter even displays the correct frequency when I transmit, but again, it does not tune and the display always shows a 1:1 match.  Any suggestions on what I should check next?  BTW - I also have the B version which works great.  This is nearly identical, except for not working as it should.
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K6SDW

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Re: MFJ-993 Tuner Problem
« Reply #1 on: September 20, 2022, 06:22:41 PM »

I assume you've tried a factory reset. I know my 939i manual describes all the different resets for my 939i. I had an issue with my MFJ switching supply so I used their email help form on the MFJ website and got a reply from their technical support folks which helped.

GL/73

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WB1ANA

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Re: MFJ-993 Tuner Problem
« Reply #2 on: September 21, 2022, 04:43:57 AM »

Yes, I also performed the full factory reset.  They have some decent built-in diagnostics and various resets for other functions, but alas, all indications are that the tuner is fine.  I think your suggestion to contact their technical support is a good one.  Based on where I am with this, I think it's time.  Thanks.

73, Tom - WB1ANA
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N4ATS

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Re: MFJ-993 Tuner Problem
« Reply #3 on: September 21, 2022, 06:33:04 AM »

What mode are you trying to use it in? I would assume FM or CW for tuning or you do have excited RF? Also are you in the pass mode?
« Last Edit: September 21, 2022, 06:35:24 AM by N4ATS »
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WB1ANA

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Re: MFJ-993 Tuner Problem
« Reply #4 on: September 21, 2022, 08:03:56 AM »

I use either FM or CW to invoke auto tuning.  In addition, it can't be manually tuned either.  But you raise a good point - it's acting like it's stuck in pass-through mode, even though it isn't.  I'll set it up exactly like my 993B is set up and try to mimic the tuning process that's working for it.  Thanks.
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AA7IS

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Re: MFJ-993 Tuner Problem
« Reply #5 on: September 21, 2022, 08:20:12 AM »

Sounds like the directional coupler has a bad diode possibly.
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