[Yaesu] MH-27 Mic DTMF inop

[GGLL]

	My 2 cents (like you use to say), common sub-miniature electrolytics 
work fine also (1uF 16V), I've replaced many of them.

The job is somewhat complicated due to the location of the beasts, but 
you can accomplish it with correct tools. Keep care to watch the 
polarity before removing them.

The worst problem is the leak inside the microphone board which destroys 
the traces and feedthrough holes. It's a slow process but if you let it 
work, this electrolytic fluid corrodes the copper.

Regards
Guillermo - LU8EYW.

El 08/03/2010 10:11, John Abbruscato escribió:
> Repairing the Yaesu MH-27 microphone to correct low audioParts
> Needed: (per mic)
>
> 1 ea. 0.1 uF Tantalum cap @ at least 10-12 volts (C5). Suggestion:
> Radio Shack #272-1069 0.1 uF Polyester Film @ 50 volts
>
> 1 ea. 1.0 uF Tantalum cap @ at least 10-12 volts (C6). Suggestion:
> Radio Shack #272-1434 1.0 uF Dipped Tantalum @ 35 volts
>
> KC2RDX, who has successfully completed the repair, wrote to say that
> he used Radio Shack parts with total success and provided the above
> RS part numbers. I checked the Radio Shack website and they appear to
> be available at most stores. Now, on to the good part.....
>
> The engineers at Yaesu, for whatever reason, used 50 volt
> electrolytics in designing the MH-27 mic. As you know, an
> electrolytic needs voltage for the capacitance to stay "formed". Well
> the 5 volts in the mic just isn't enough and they gradually lose
> their ability to pass AC signals. This prevents audio from the mic
> getting to the radio.
>
> You will be working with Surface Mount Technology here, but the caps
> that need replacement are fairly large in size. Open the mic by
> removing the three external screws; one in the hangup button and two
> in the black plastic case. Gently unplug the mic cord and set it
> aside. Remove the three smaller screws in the PC board "sandwich".
> The "on air" LED, the electret element and the UP/DOWN switches are
> not physically attached to the case so they may be pulled from their
> locations. You can now remove the PC boards leaving the rubber
> keyboard membrane in the case.
>
> The boards are held together by headers at each end - a 2 pin header
> at the top and a much larger one at the bottom near the mic cord
> plug. Use a solder sucker or solder wick to free these. You may now
> separate the two boards. On the inside surface of the back board, you
> will see 4 black cubes approximately 3/16 inch on all sides. The two
> that are right next to each other are the audio coupling caps. With
> the mic cord connector facing downward, the one for the mic audio
> (C5) is on the right and is nearest the edge of the board. The one on
> the left and closer to the center of the board is C6, the Touch-Tone
> (TT) audio cap. Mine were marked "1R" and "1".
>
> Simultaneously heat both terminals on the end of C5, the outboard
> cap, and remove it. Replace it with the new 0.1 uF cap, observing
> polarity if applicable. Tack solder. Neatness counts! Also replace
> the 1.0 uF TT cap (C6), the inboard one of the pair, while you're in
> there. Even if your tones are working now, their days may be
> numbered! Remember that C6 is a 1.0 uF cap, not a 0.1 uF.
>
> Make sure nothing is shorted and solder the two boards back together.
> Screw the boards back into the mic. Re-install the electret element,
> the "on air" LED and the UP/DOWN switches. The pot you can see after
> re- assembly is for Touch-Tone audio only. There is no pot in the mic
> for voice audio. Re-install the mic cord and test it. See note below.
> If all is well, close it up.
>
> NOTE: Although not likely just because of the cap replacement(s),
> audio levels may need adjustment. There is a pot internal to the
> radio that controls ALL audio coming from the mic. Adjust the
> internal radio pot for voice level first, then adjust the pot in the
> mic for TT level. Since the MH-27 was used on more than one model of
> radio, you're on your own in locating the internal radio pot. If you
> can't find it, just adjust the mic pot for TT levels. Again, level
> adjustments due just to cap replacement will not likely be needed.
> But, if like me, the first thing you did to try and get your voice
> audio back was to adjust the pot in the mic, you may have changed the
> TT levels.
>
> --- On Sun, 3/7/10, LHOTP at ATT.NET<LHOTP at ATT.NET>  wrote:
>
>
> From: LHOTP at ATT.NET<LHOTP at ATT.NET> Subject: [Yaesu] MH-27 Mic DTMF
> inop To: Yaesu at contesting.com Date: Sunday, March 7, 2010, 9:56 PM
>
>
> The DTMF on my MH-27 microphone is intermittent/ weak at best; voice
> reports are A-OK, so I assume the problem is isolated to the DTMF
> portions of the circuit board.  I looked online and found that one
> likely bet is aged capacitors.  I don't have the skills to R&R the
> capacitors myself.  The mic is attached to a FT-2500M, if that
> matters.
>
> Does anyone know of a place to have it repaired for a reasonable
> price? I'd rather not spend more than about $30 to fix it when a new
> 2m is barely four times that price.
>
> Jon KE5WGZ _______________________________________________ Yaesu
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