Subject:MAXAR temp drift mod This file contains information to REDUCE the amount temp drift that the Motorola Maxar series radios exhibit. This is a proven modification, however, Iam not responsible for anything contained in this information. From day one, the Maxar series of Motorola radios have had a temperature_0 frequency drift problem. Motorola is aware of it and has issued Tech Bulletins on the subject. None of the Tech Bulletins corrected the problem as well as the following mod does. The Motorola Maxar 80 radio has a built in temperature_0 compensating REGULATOR built into the radio. This regulator works below -10 degrees C. Therefore, the crystal temperature_0 in Not maintained under most normal operating conditions. The heart of the regulator consists of a resistor and an NTC thermistor. Basically, the increase of temperature_0 at the crystal increases current flow thru the thermistor which decreases current flow thru the resistor which lowers the temperature_0 of the crystals. The values of the standard components cause the "idle" point of the circuit to be somewhere above -10 degree C. When the temperature_0 drops below the "idle" point, current decreases thru the thermistor which increases current flow thru the resistor which heats the crystal. The concept of this mod was to merely increase the "idle" point of this circuit to insure that the NORMAL average conditions could be delt with in a reasonable way. During this mod, it was also found in the original design, that the regulator is wired to switch battery. this mod also corrects this. TOOLS AND SUPPLIES NEEDED: a. Soldering iron b. Solder c. Short length of hook-up wire....6inches??? #20 d. 2k ohm 1/4 watt resistor e. Sharp knife or razor f. Manual on radio you have A) Locate the TRANSMIT crystal. You should find a resistor right next to it. Directly under the resistor, you should find the thermistor. it is usually wrapped in heat-shrink along with the resistor. Also locate this on the schematic in the manual. It is located in the UNIFIED CHASSIS, exciter section. B) Locate the trace going to both RT101 and R135. Cut it. C) Add a jumper wire from the junction of RT101 and R135 to A+. Before you cut the trace, the junction was wired to SW A+. Make sure you wire to A+, NOT SW A+. D) Locate the other side of RT101 and the trace. Cut it and clean both sides of the trace for soldering. E) Add the 2k resistor across the cut you just made. ****YOU ARE DONE**** NOTES: As best I can tell, the crystal temp is now maintained at 80 degrees F. I have done this mod to a couple of radios and have not had to adjust the freq since...bout 2 years! This mod does increase the idle current flow of the radio. Not much but you dont get something for nothing. 73 de Jim, WA6OFT @ KA6HMG.AZ.USA.NA  Amsterdam View Our Stats   CLICK FOR A FREE DOMAIN NAMES HTTP://WWW.YOURNAME.TK FOR YOUR OWN WEBSITE IF YOU CLICK HERE AND YOU CAN VOTE FOR OUR FREE WEBSITES IN THE TOP 100 LIST  WANT A TOP RANKING ? USE THE ULTIMATE SOFTWARE SUITE FOR WEB SITE PROMOTION  FreeWebSubmissions Submit Your Site To The Web's Top 50 Search Engines For Free THE ALEXA BANNER, THIS BANNER GIVES THE DALLY STATISTICS OF THIS FREE WEB SITE The World of Free Packet Radio Software Amsterdam The World Of Free Packet Radio Software Amsterdam The Netherlands |