RCI-2950 Improvement Modifications
Problem: Noisy receiver. Unit has a high level of vehicle noise (i.e., Fan noise. Electronic Fuel Pump noise, etc..)
Cure: To reduce front end overloading on the RCI-2 950 (i.e., quiet the receiver) change R78 from a 2.2K resistor to a 10K resistor. This modification will reduce the bias on the first RF Amplifier, Q18, thus aiding in reducing impulse noise created by the various electronic or electric components in the installed vehicle. In some of the more difficult cases, a .047 uf electrolytic capacitor may need to be installed across the power terminals of electronic fuel pump or fan motor. Additional filtering may be also required across the radio's DC input. Any good commercial filter rated at least 15 Amps or higher can be used.
Problem: Stations close by sound distorted or garbled. However distant stations sound O.K.. Automatic Gain Control does not seem to be functioning properly.
Cure: To reduce the effects of A.G.C. overload on receive, change R49 from a 100K resistor to a 33K resistor. Normally this will cure the problem in most units. In some units it will also be necessary to change R78 from a 2.2K resistor to a 10K resistor in order control front end overloading of the receiver.
Problem: Unit fails to operate on initial turn on. Turning the radio off then back on causes the radio to operate.
Cure: This problem is usually caused by the V.C.O. being out of lock. In order to prevent future occurrences, it will be necessary to change C107 to a lOOpf NPO disk capacitor. Once this capacitor has been replaced you will need to readjust the V.C.O. voltage. Locate J13 and connect a DC volt meter between it and ground. Set the radio to 28.0 MHz and then adjust L17 for a 1.9 volt reading on the DC volt meter.
Problem: The Variable Frequency Adjust located above the microphone jack does not operate properly. Several clicks are required before the frequency changes.
Cure: A resistor change will be required in order to cure this problem. Locate and change R611 on the microprocessor board from a 47K Ohm chip resistor to a 10K Ohm chip resistor. If a 10K Ohm chip resistor is not available a standard 1/8th watt 10K resistor can be used.
Problem: Premature battery failure.
Cure: The lithium memory battery which is installed on the microprocessor should have a normal lifetime of 2 to 3 years under normal use. One cause for premature failure of this battery is the excessive use of the reset switch (S601). This switch can be used to disrupt the normal power up and power down initialization process that the microprocessor executes. One alternative is to advise the customer of this problem and to avoid excessive use of the reset switch. The best solution is to remove S601.
Battery Replacement Procedure for RCI-2950
Remove the defective battery, and replace. After the new battery has been installed it will be necessary to re-initialize the microprocessor for proper operation. To do this turn the unit on and then back off again. Once this has been done turn the unit back on and check for proper operation. If all functions seem to be operating then turn the unit off and allow it to set for about 5 minutes or so. After the unit has set for this period of time, check the voltage of the new battery in order to make sure there are no shorts which are causing the battery to fail. If the voltage begins to drop , the microprocessor may be defective and will need to be replaced.