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Author Topic: MFJ-993B Tune function  (Read 1080 times)
WA7KGX
Member

Posts: 104




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« on: October 05, 2013, 01:22:25 PM »

Some time ago I got an MFJ-993B auto tuner and cable for my 756 Pro.
One of the features is support for the 756 Pro's TUNER button.
Pressing that button initiates a tuning cycle.

Recently the tune cycle initiated from the Icom stopped working.
The radio never goes into a transmit mode and the 993B displays
"Huh?  Increase power".

If I transmit a carrier the 993B can autotune if I hit the TUNE
button on the 993B.

Does anyone have a schematic for the 993B?  It looks like
an output transistor is open.
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AC4RD
Member

Posts: 1235




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« Reply #1 on: October 06, 2013, 05:59:21 AM »

You've probably already done this, but just in case:  take a look at the MFJ website.  There are a lot of schematics available there, often inside the products' PDF manuals.  GL!
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WX7G
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Posts: 6134




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« Reply #2 on: October 06, 2013, 06:46:50 AM »

The MFJ-933B manual has no schematic. Have you tried resetting it and a self-check? Pages 26-28.
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WA7KGX
Member

Posts: 104




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« Reply #3 on: October 06, 2013, 08:05:48 PM »

The MFJ-933B manual has no schematic. Have you tried resetting it and a self-check? Pages 26-28.

Tried both.  No errors reported.
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WB2EOD
Member

Posts: 219




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« Reply #4 on: October 07, 2013, 05:26:12 AM »

I have the 998 which is the high power version of yours.
Normally the tune cycle causes the rig to put out a 10 watt carrier which the tuner needs in order to work. 
If the initial mismatch is so far off that the radio won't put out the 10 watts then you will get the "increase power" message.  I get this on 80 meters where the antenna bandwidth is narrow. 
My solution is to simply throw a carrier and let the tuner do the work.
A minor annoyance but better than fiddling with an inductor and 2 capacitors

Hope this helps
73
WB2EOD
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