RCI 2950DX Image Rejection Modification

As noted in the review, an anomaly, not found in other radios, was found in two of the RCI 2950DX tested. Further test determined signals outside the passband of the 10.965 crystal filter were indeed getting through or around this filter. All the components and every circuit trace was followed per the schematic diagram. No component failures were found. In addition, no visible faults were found with the circuit board following the schematic diagram. However, the circuit board diagram indicated a resistor R325 location under FL3, the 10.965 crystal filter. Removing FL3 was more difficult than anticipated due to the double sided circuit board. Once removed, the R325 location was revealed and empty. Testing the radio with the filter removed showed the same image problem was encountered. Probing the area of R325 with test equipment indicated the sensitivity of the circuit. The closer test probes got to the pads of this resistor, the higher the signal strength on the radio LCD meter. This concluded the remedy needed. As explained in the RCI 2950DX review, Ranger Communications could not duplicate this problem. This means they do not acknowledge this problem. No doubt this will not be covered under warranty. In addition, if not properly done, it may indeed void the warranty. The following modification portion of this article describes and illustrates how to perform the modification, but due to the double sided printed circuit board, it is very difficult to remove the FL3 crystal filter without damaging the circuit board! THE FOLLOWING PROCEEDURE SHOULD ONLY BE DONE BY A QUALIFIED TECHNICIAN WITH EXCELLENT SOLDERING SKILLS!!! CB World Informer or the author cannot be held responsible for any damage or loss of warranty! Now that I've scared the the stuffing's out of you, lets get back to the mod so you understand what was done to the test radio.. As mentioned above, this is a double sided circuit board. The heavy ground plane is where the most difficulty will be found. It requires a great deal of heat to melt the solder on the other side of the board in order to remove it with an extraction tool. A high wattage soldering iron used for only as long as necessary should be used. That's where the experience comes in. If you leave the iron on too long the circuit board will burn and the traces will lift of the board. Even if it's patched up, if noticed during a warranty repair, RCI may deem the radio out of warranty and then you're SOL. In addition, if there is still solder holding the filter and you pull it out only to find it's missing a pin or two, ditto! Please leave this one to the professionals. All radios that incorporate this main circuit board have been and will continue to be modified by Bob's CB & Wireless prior to sale at no additional charge. If you own a RCI 2950DX, 2970DX, 2985DX, 2990DX, Bob's CB & Wireless offers this modification at $25.00. http://www.bobscb.com/contact.htm As described above, the crystal filter FL3 must be removed. There are two traces from R325, one connects to the input of the filter and the other connects to the output of the filter. Both traces can be pealed up using a xacto-knife. Remove the resistor pads and traces back to the filter connections cutting the traces off at the crystal filter pads. See diagram and photos below.

FL3 Section Of Circuit Board Diagram

FL3 Component Side Of Circuit Board.

FL3 Removed From Circuit Board.

R325 Traces Removed From Circuit Board.

Once the traces are cleanly cut, the monolithic crystal filter can be reinstalled. Test and reassemble radio. Tuning is not necessary. Bob F

September 2001 Web Edition