Has your Sharp MD-MT831 unit "mysteriously" turned itself off? While recording? While Playing? Won't turn on at all when powered from AC Adapter? Read on!
I recently purchased a SHARP MD-MT831 MD Recorder from Japan. I have discovered a potentially SEVERE situation with the factory supplied "Wall Wart" Power Adapter. The problem (I believe) is an over-voltage protection device inside the 831. If the voltage is TOO HIGH -- IT WILL NOT WORK PROPERLY.
I BELIEVE RUNNING YOUR 831 FROM THE SUPPLIED AC ADAPTER PLUGGED INTO THE UNIT DIRECTLY (IN THE USA!) **COULD** POTENTIALLY CAUSE PERMANENT DAMAGE TO THE 831 UNIT!
Because of "slight" differences in the AC Mains Power-- [the AC voltage at your wall outlet] [USA=115-120 Volts AC vs. JAPAN=100 Volt AC] --it puts out TOO MUCH VOLTAGE! Please note that AC Mains power can vary from city-to-city, house-to house, and OUTLET-to-OUTLET!)
The AC adapter supplied with the SHARP 831 is specified as "5 Volts DC @ 800 ma". The 831 Recorder & Cradle Specifications call for 5 Volts DC.
I have measured the output of the adapter that comes with the SHARP 831 and it puts out a MINIMUM of 6.97 VOLTS (open-circuit)! It is normal for these "wall warts" to put out a higher voltage than specified, as most are NOT regulated. However, I have found that at certain times of the day, the unit that came with my 831 puts out MORE THAN SEVEN VOLTS. That's TWO VOLTS MORE than specified! That's a 40% difference. **I** do not feel to safe with those numbers.
NOTE: "OPEN CIRCUIT" means measuring the Adapter without anything connected, also called "no-load".
Another discovery, If you power the unit from AC, **OUT-OF-THE-cradle, the unit will give an ERROR MESSAGE. I've found this is especially true if the battery has a full charge.
You will get the error when you attempt to use the unit. When you attempt to turn the unit on, it will display "POWER?" on the (main) display, an error message, (I can only assume), then quickly turn itself off. It will just plain refuse to work. Or it will just stop recording and/or playing for no apparent reason.
What's the solution? I have found two.
WHENEVER YOU PLUG THE 831 IN THE WALL-- ALWAYS POWER IT "THROUGH" THE CRADLE!
I have found that if you run the 831 from AC Power **IN-THE-CRADLE**, the problem goes away. HOWEVER, I do not feel comfortable with this. I have opted for solution #2 below.
GET (or BUY) A NEW AC ADAPTER
I found an AC adapter that has the SAME CONNECTOR (4 mm OD/1.7mm ID, Center-POSITIVE/Yellow Insulator with two small notches in the barrel). This new unit is rated at 5.5 Volts DC @ 800 ma. Measured (Open circuit) voltage is about 5.75 Volts. With this AC adapter, the unit seems to operate just fine, in or out of the cradle.
Where do you get one? The one I have is for my Mitsubishi Cell Phone, but I checked the Radio Shack catalog and they have a unit, WHICH I BELIEVE WILL WORK, YOUR MILEAGE MAY VARY, and STANDARD DISCLAIMERS APPLY.
The adapter is Part Number 273-1667 ($14.99 US$) along with 273-1705 AdaptPlug (I THINK) BRING YOUR UNIT IN TO MAKE SURE. I have just looked in the catalog and *NOT* actually tried this setup!
The unit will provide various voltages: 3, 4, 4.5, 6, 7.5, 9, and 12 Volts DC at 800 ma. The unit should only be used at the 4.5 Volts DC setting. (If this does not work, you can TRY the 6 Volts DC setting but ONLY if the 4.5 Volt setting does not work). This 6 Volt setting EXCEEDS the 5 Volts DC factory spec of the 831.
I feel the unit SHOULD operate satisfactorily at 4.5 Volts DC. Again, ALL OF THIS IS DONE AT YOUR OWN RISK! I ASSUME NO RESPONSIBILITY FOR ANY DAMAGES OF ANY KIND!
Other option would be to track down a 5-volt unit from someone like JAMECO at "http://www.jameco.com". I hope this sheds some light on any problems (or potential problems) you may have.