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Tim Landers, N4HIG |
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Decatur, AL |
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I have a Yaesu 5200 dual-band rig that has an MH-27 microphone. A while back, the audio from the voice element got low, but the DTMF tones sound fine, which seems to eliminate most of the audio circuitry. I have seen postings on the net, and talked to Yaesu, and the story is that the element is not usually the problem, but rather 3 capacitors become leaky. I tried replacing the two I could figure out from the board and the schematic, but I can’t figure out what device is the 100 pF labeled as C1 in the schematic. I’m not an expert on SMDs. So I need help finding this cap, and suggestions as to where I might order the parts in small quantities without paying a fortune for shipping. Link to the picture: Link to the schematic (PDF): |
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ALERT! I have received several hints from others who have succeeded at fixing this problem. I have placed edited versions on the following pages. I have also corrected the picture of the components that might need replacing, but it seems the consensus is the .1uF is the likely culprit If anyone objects to your message being posted here, let me know and I’ll remove it. |
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RE: MH-27 Microphone Help From: Tim Landers Sent: Thursday, September 27, 2007 11:50 PM To: Luetz, Tom Tom: I kind of got started, and got some info from Bryan, WA7PRC on the alt.ham-radio forum: In your image, the capacitor you have marked as C5, appears to be C1 and should be 100pF. C5 is to the right and above the resistor marked "222"(2200 ohms). It's a 0.1uF/50V tantalum, marked "R1/50V". I also noticed it has the terminals on the same end of the device; nowadays, tantalums typically have the terminals on opposite ends of the package. I doubt you'll find it. However, it appears you may be able to fit a much easier to find ceramic capacitor in there... probably a 1206 (0.120x0.060") package. The leakage will be much lower than that of the best tantalum. DigiKey (http://www.digikey.com/) has a $5 surcharge on orders under $25(and may require you to buy in increments of 10 pieces). Try Mouser(http://www.mouser.com/) instead. Bryan WA7PRC Some other projects have taken priority, but I still want to fix it. I guess my main concern is the 0.1 uF/50v electrolytic. I have the other two as ceramics. I'd like to compare notes and see what you did to maybe do it better. thanks! Tim N4HIG |
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RE: MH-27 Microphone Help From: Luetz, Tom Sent:Thu 9/27/07 11:47 PM To: Tim Landers I found the problem to be the 0.1uF cap (the "R1/50V"). Looking at it under a 15x magnifier showed that it had either leaked or somehow developed corrosion where the leads exited the body. This value of this coupling cap, which serves to isolate the AC voice output signal from the DC bias power, isn't that critical. I replaced it with a 4.7uF 10V electrolytic from an old CD player. If you look here: Drop me a line if you need more help. Tom |
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Re: MH-27 Microphone Help From: Magnu96196 Sent:Sat 11/03/07 7:26 AM To: Tim Landers
In a message dated 11/03/2007 2:25:26 AM Eastern Standard Time, pnnfc@hotmail.com writes: << I suppose I'll take the page down now. >> Don't take it down---just update it----point to the 0.1 uF being the problem. Then all can repair their MH-27's easily. Sounds like Yaesu got a huge bad lot of those caps. "KEMET" is brand name for tantalum caps that will fit the pads---but I like the ceramic fix better as that will never go bad again. One the second mic, I was able to only desolder the two pins on the top side of the mic apart and lean the boards apart enough to get the 0.1 uF unsoldered and the new NP ceramic cap back in its place. That lower pin header row is hard to get loose even with a solder sucker. |