General CB Radio Repair Tips
We've had several sets of various make with the following fault: No transmission or low or erratic RF output. In most cases the ON/OFF switch was faulty. Audio output is often not affected. Note, however, that a faulty R.F. output or driver transistor can produce the same symptoms.
Use a bridge rectifier to protect rig against reverse polarity.
Noisy crackling from a microphone switch can, in most cases, be cured by applying a light oil or WD40 to the contacts. It can also be used in crackling squelch or volume controls and to clean the outside of rigs and improve the clarity of channel displays.
Instead of having several power leads with different plugs trailing across the repair bench, cut all your power leads down to 6 inches and fit them to a connector block with just one pair of wires going back to the power supply. This idea makes it easier to find the correct plug and is much tidier.
Mic socket pins which are split can close up and cause a bad connection. Similarly, aerial socket segments can open out and cause a bad connection.
When knobs are loose, instead of wrapping tape round control spindles, insert a screwdriver to open the slot.
If the "S" meter lens is scratched, use 400 grade abrasive paper until the lens is opaque, then polish with Brasso. Sounds extreme but works easily and quickly!
Instability on TX or intermittent TX can be caused by loose screws holding PCB to chassis. This fault has been found on Cobra 148, Superstar 120, Superstar 360, President KP77 and is known to occur on many others.
Multimodes - To convert Fine-Tune into a KC shift, trace the centre connection from the pot to the varicap diode. There is usually a diode in this lead so the pot is only in circuit on RX. Wire the pot straight to the varicap diode. One end of the pot will be grounded and the other will have no connection. Connect the n/c side to the 9v regulator to give 4kHz shift each way.
WARNING Some power transistors and regulators, apparently, contain poisonous substances so be sure to wash hands and nails meticulously after handling broken or cracked devices.
A danger exists on some homebase rigs and power supplies. They have only two-core cable or switches in the neutral wire! Also earth tags should be bolted to chassis, NOT pop-rivetted to a transformer lug.