From philabs!philmtl!uunet!ginosko!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!att!cbnewsc!parnass Mon Aug 21 09:22:10 EDT 1989 Article 13545 of rec.ham-radio: Path: philabs!philmtl!uunet!ginosko!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!att!cbnewsc!parnass >From: parnass@cbnewsc.ATT.COM (Bob Parnass, AJ9S) Newsgroups: rec.ham-radio Subject: Longer battery life for the Regency MX-4200/MX-4000 Keywords: scanner radio, NiCd battery charging Message-ID: <2544@cbnewsc.ATT.COM> Date: 18 Aug 89 19:16:57 GMT Organization: AT&T Bell Laboratories Lines: 100 Posted: Fri Aug 18 15:16:57 1989 x GET LONGER BATTERY LIFE FROM YOUR REGENCY MX-4000 OR MX-4200 SCANNER by Bob Parnass, AJ9S The discontinued Regency MX-4000 and MX-4200 are battery operated, 20 channel scanners manufactured in Japan by AOR. Both scanners contain a low battery warning circuit which disables the scanner when the battery voltage falls below a preset level. A freshly charged battery pack should last at least 5 hours before needing a recharge. Ron Smithberg, of Joliet, IL, complained of getting only 2 hours use from a set of freshly charged NiCd batteries in his MX-4200. This article describes how we increased his usage to over 7 hours between charges. Both MX models are powered by a pack of 4 AA sized NiCd batteries. The battery pack is nominally 4.8 volts and has a rated capacity of about 500 mAh. The scanner draws about 100 mA when squelched. A good rule of thumb is that a NiCd should be recharged when its voltage falls below 1.0 volts per cell. Using this heuristic, the MX- 4200 battery pack should be recharged when it falls below 4.0 volts under load. The low battery circuit on Ron's MX-4200 was misadjusted to shut down the scanner prematurely when the battery voltage fell below 4.7 volts. I readjusted the low bat- tery threshhold to 4.0 volts. You can use the same procedure, but you will need the following equipment: o An adjustable, regulated DC power supply, capable of furnishing between 3 and 5 volts at 500 mA or more. o An accurate means of measuring voltage from the power supply. A digital voltmeter with an accuracy of 5% or better is preferred. o A #1 Phillips screwdriver. o A Small, slotted screwdriver or alignment tool. The low battery sensor threshhold is controlled by a potentiometer. Here's how to readjust the sensor to 4.0 volts: 1. Turn the scanner off. 2. Connect a digital voltmeter to a well regulated DC power supply and adjust the supply to 5.0 volts. 3. Connect the power supply to the snap terminals on the scanner that would normally connect to the bat- tery pack. Be sure to observe proper polarity. Connect the positive lead of the supply to the female snap, and the negative lead to the male snap. 4. Turn the scanner on. 5. As you watch the scanner's LCD display, gradually reduce the power supply voltage until the scanner's low voltage warning begins to flash. 6. Read the digital voltmeter. If it reads between 3.9 and 4.0 volts, no further adjustment is required, just disconnect the supply and reconnect the battery pack. 7. Otherwise, turn off and disconnect the power supply, and continue. 8. Turn the scanner upside down, and place it on a soft cloth so as not to scratch the case. 9. Remove the bottom tilt foot from the scanner. 10. Remove the battery pack. 11. Remove the 4 Phillips screws holding the case bot- tom, then remove the case bottom. 12. Reconnect the power supply to the scanner and set it to 4.0 volts. 13. Turn the scanner on. 14. Locate a small gray potentiometer on the printed circuit board. The potentiometer looks something like a gray plastic Phillips screw head. If the scanner front panel is facing you, the pot will be just behind the keyboard on the left side. (Don't confuse this pot with the 3 pots along the right edge of the board. The battery voltage sensor pot is not near any other pot.) 15. Slowly adjust the potentiometer to the threshhold at which the low battery indicator begins to flash. This procedure worked with great success on an MX-4200, and its battery life was increased from 2 to 7.5 hours. I would like to thank Rick Meyer, WB9UFL, for finding the potentiometer in his MX-4000, and Ron Smithberg for let- ting me experiment with his MX-4200. -- ============================================================================ Bob Parnass, AJ9S - AT&T Bell Laboratories - att!ihuxz!parnass (312)979-5414