Always check and replace cross connection protection diode
Prestige Models Include

Audioline 340/341
Uniden Uniace 100/200/400
Crystal Filter
If you use a 1K impedance crystal filter from PR Gollege simply
replace the ceramic filter and re-tune L4 and L3. If you use the early
Ambit 3Kohm crystal replace L4 with a TOKO KACSK3892A transformer (red) and re-tune L4 and L3. The new L4 will normally need to be screwed
downwards. If distortion is evident disconnect the track between the filter and L3 and re-connect the filter to the un-used pin of L3 which is a higher
impedance point. If you use the later 1K8 Ambit Filter you may get away with the standard L4 but if distortion is evident replace it.
RF Gain Control - For the smaller rigs (Audioline 340) you can make an RF gain switch by cutting through the resistor in series with the squelch pot. You
could use the tone switch to make the resistor switchable.
The larger 341 and its equivalents have a very "Harsh" RF gain action can be vastly improved by replacing R2 (1k5) with about a 6k8 resistor giving it a
much smoother operation.
D1 goes open circuit causing lack of sensitivity. You may need to replace this with two ordinary diodes in series. D9 can also go open circuit causing the
same effect
Squelch control
The squelch control can be a bit dismal on the audioline/uniden type rigs and can be made much sharper by replacing C5 (10uf) with a 1uf. C5 is in the
vicinity of the center of the PCB just behind the loudspeaker clearence area.
VCO locks on TX but not RX
Replace TR18 (92SA1015)
No RX - and both TX/RX lights on
Replace TR17 (2SC1815)
RX jumping in and out during TX
Both TX and RX lights on and rig will not lock. Removing RX wire from mic socket allows normal TX operation. Replace Audio IC.
President KP77 Homebase
"Motor boat" effect on some channels with loss of power. Replace TR202 in PSU board (PC-410AC) with TIP41
Convert to FCC Frequencys (Mid Block)
Connect the TC9106 PLL chip directly on top of the TC9119  piggy back style but leave pins 3, 4, 5, 6 and 7 free. Cut track to pins 4 and 5 on TC9119. Link
TR17 collector to junction of D6 and R33. Connect pin 5 of TC9106 to the bottom of your new bandswitch. Connect pin 5 of TC9119 to the top of the
bandswitch. Connect the track previously disconnected from pin 5 to the bandswitch slider (middle pin). Change C62 to 18pf. Solder 33pf cap across C64.
Tune VCO if Necessary and output coils for operation on both bands
Audio IC gets very Hot
Replace R93 which burns out (middle of PCB)
TX lights stuck on
Weaker signals cant be heard. Replace TR17 and TR19 (middle of PCB)
No TX but RX ok
Voltage on pin 8 of PLL should be 0v on Rx and 7.4v on TX. If the voltage is much less than 7.4v try replacing TR18 (2SA1015) which is a PNP transistor
No Sound
Like a blown audio IC. Try IC1 in front of discriminator can (after checking for dry solder joints and ext. speaker socket + mic)
Uniden PC40
Remove 10k resistor (near front of PCB on track side) to give full 40ch on AM.
Low and Distorted Audio
Remove mic insert PCB and locate coil from earth pin to black wire (0v) replace this coil or link it out.
Uniden 400
Shorts power supply or blows fuses when switched on. Change un-marked diode next to JP2 at rear of PCB
No Mod on TX
Replace IC4 (4558D
Transmitting without mic
Replace TR17 Transistor
Very low RX
Replace Diode D1
Faulty Squelch
On audiolines the Squelch is soldered to the front PCB and can become easily detached. Likewise the RF/Mic gain

TR18 can be replaced with a 2SA733 as it is the default transistor in my Uniace 200. you can buy the 2SA1015 and the 2SA733 from kcb.co.uk. Funny how
the 1015 is 40p and the 733 is 85p tho... (Thanks Jason)
CB Radio History from its early days
CB Radio Repairers in the UK