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CB Radio History from its early days
CB Radio Repairers in the UK
JWR M2 - To improve squelch, replace the 470R resistor beside pins 9 and 10 with a
higher value
Rig lights up but no TX or RX. Try replacing D203 (5v6 zener diode)
No TX can be caused by the demise of R327 and R217.
Fluttering oscillation on both RX and TX , replace audio IC (Also Icom).

On AM rigs, no audio and RF carrier output and no audio on TX normally solved by
replacing the audio IC.
Low TX and low RX can be caused by a faulty RF output Transistor, especially in
Stalker 9 type radios.
Rigs keep blowing fuses. Check insulating washers and bushes on ALL heatsink
transistors
Make your own low power Dummy Load - By soldering 20 x 1k resistors in parallel (found in most scrap CB's). As these are ¼w
then 20 of them would make the dummy load OK up to 8w.

Handy Hint - Fit an signal meter bulb at the end of a ballpoint pen tube to help read component numbers deep within a CB.

Fidelity 1000/Cheiza etc. - Signal meter indication but no incoming sound, replace Q8
Transmitted modulation low or zero, replace Q11.
Change binary codes to get mid block (Order DA3 conversion)

Jesan KT-750 - Emergency transceiver. Weak modulation, link out R25 (18k) and adjust RV1.
This set also had very low power output which was caused by a bad solder joint on C71 which is located near the output transistor
Q13 (2SC2078)

Fidelity 1000/Cheiza etc. - No incoming sound but signal present, change Q8 (after making sure the speaker and Ext. Spr socket are
both ok)
No gain on mic or very little, change Q11.

COMMON FAULTS ON TRUCKS:

CB radio lights up but no sound. Only a slight click heard from speaker when switched on, voltage over 16v will cause this, check
the power coming out of your 24/12v dropper.
CB radio lights up and seems to get out well when engine is off. Signal meter registers over 5 on a clear channel. Can be caused by
an under-rated dropper or heated mirrors, try a bigger dropper or mag mount.
CB radio buzzes on TX but only on high power setting, try replacing dropper for a higher rated one, this can also be caused by the
dropper being too close to the mic socket.
On ERF and Foden fibreglass cabs, place the magmount in the centre of the sunroof. If there is no sunroof pop rivet a sheet of 2ft
square steel on the centre of the roof and put the magmount on that.

Audioline CB - Audio IC gets very hot, replace R93 (burnt out) in the middle of the PCB.
TX light stuck on and weaker signals can't be heard. Replace TR17 and TR19 in the centre of the PCB.

Midland 2001 - No squelch, try replacing MC3357. No TX no RX no incoming signals on meter, try replacing 2SC7808 on the side of
CB.

Any CB Homebase - BEFORE plugging it in make sure the PSU has not been removed and converted to run off 12v. It has been
known.. bang!

Fidelity 2001 - (Amstrad board) No channel display, try D400 at the front end of the board or D3.

Fidelity 1000 - No channel display, no RX or TX. Try replacing Q9 and D11 on centre right hand side of board.
No squelch, try replacing Q7 in front of the audio IC.

Harrier CBX - (134 board) No squelch but squelch transistor OK. Pot is OK, try replacing 7205 Audio IC.
No RX or TX, sometimes keys up on only 1 channel. Channel changer appears not to work, try D2 (6v2 zener) next to LC7132 IC. If
this is faulty the voltage on pin 18 of the 7132 will be well below 6v.

MOD MODS:

Improve modulation on Grandstand Hawk/Lowe TX40 by replacing C148 (10nf) and C139 (10nf) with 100nf. Replace R110 (47k)
with 100k and adjust deviation pot VR4.
Amstrad 900/901, Mustang 3000, Fidelity 2001 etc (Amstrad board) add 100nF across C29 and C31, adjust deviation pot RV3
Superstar 2000/Tristar 777/Nato 2000, add 100nF across C151 (22nF) C149 and C155 (47nF).
Colt 747/Hy-Gain 5, add 100nF across C160 and C162 (22nF)

Colt Excalibur SSB PTBM 121D4X - Add a switch in line with R185 (330k) or C207 to make the roger bleep optional.

Fidelity 1000/Academy etc. - RX ok but no signal indication, replace D5.
R65 (8.2 Ohm) burns out causing no TX. This resistor is located close to Q19 output transistor. Replace with 1 watt resistor or two
0.5w 18 Ohm in parallel.

LCL 2740 DNT - No TX but meter indicates normal operation. On these rigs the meter is driven via diode D15 and preset R98 (100
Ohm).The voltage, however, is taken from the driver stage and not from the output stage as with most other CB's. The fault can lie
anywhere between the driver stage and the antenna socket but is usually the output transistor itself.

Communicator NI-440 DX/Serpent/Planet - No RX or TX but the radio lights up. Try replacing the 7808 voltage regulator which is
identified on the PCB as Q21 which is located in front of the audio IC.

Cheiza/Fidelity 1000 etc. - Very low or low modulation can be caused by Q13 going short circuit. The transistor is next to the
deviation pot VR3
Stuck on TX but frequency not correct, the fault is caused by zener diode D11 going open circuit. D11 is located in front of Q9 voltage
regulating transistor.

Cybernet/York/Rotel etc - No TX but RX OK, VCO frequency is OK on RX but nothing on TX. Replace faulty TX switching transistor
Q2 (JC502) located to the rear of the VCO can.
Red trimmer capacitor used to reduce VCO frequency on TX can malfunction if seated with wax causing intermittent TX. Fit new
trimmer capacitor or remove old one and repair as follows: Heat centre with a hot soldering iron then quickly spray with a switch
cleaner at close range. Repeat until no wax is left.

Audioline 340/341 etc - PA034 and PA039 Chassis. No TX but RX OK. Voltage on pin 8 of TC9119 should be 0v on RX and 7.4v on
TX. If the voltage on TX is much lower than 7.4v then try replacing TR18 (2SA1015) PNP transistor.

Rama Echo Chamber - (and similar) Not working at all. No LED lighting , RF choke coil in 0v line goes open circuit. Bridge it with a
wire link or a coil from a scrap CB.

RA201 Reverb - Blows fuses. The transistor at the front of the PCB is actually a S.C.R. thyristor. Remove it and the reverb will work
OK. Replace it to give over voltage protection again.

Most Rigs after Mid Blocking - if no UK frequencies, add a small value capacitor between pins 19 on LC7132/7132 PLLs.

Ham International Jumbo/Colt Excalibur/Marco Excalibur - LED display can be replaced with one from a scrap Fidelity Homebase

PSU Test - After repairing a PSU connect a 12v car indicator bulb across the output to test it under load. On PSUs over 3A use a car
headlamp bulb.  
Superstar 360/Cobra 148 - No audio on AM TX but everything else OK, Try 2SA1012 on the right hand side of the board. This also
causes no TX but RX OK.
No TX but RX OK, monitoring rig reveals very low signal. OK on SSB but no AM or FM modulation. Replace TR51 (2SA1012) with
TIP42 or BD712 (PNP)

Concorde MK2 - No TX on AM/FM but SSB OK, change voltage regulator 2SD837 on the back plate of the radio. This is a 'Darlington
Pair' transistor and must be replaced by the same type.

Midland 77-104 - Very common fault RX and TX goes on and off, dry joint on centre of board or voltage regulator 7808.

Audioline 340 - No RX (same symptoms as blown audio IC) try IC1 in front of discriminator can.

Midland 77-099 - No channel display or only counts up to 9, try D302  (8v1 zener diode) or R310 which burns out. Both are at the
back of the mic socket.

Transit 40FM - Stuck on 1 channel and up/down buttons seem not to work, Try re-soldering solder joints on the back of the up/down
channel board. They tend to break away very easily.

Antenna Fault - Transmitted audio breaks up especially when vehicle is moving and the mic checks out OK. Very common fault with
base loaded antennas. The coil is broken.

General Mic Fault - No audio, if mic is OK check speaker. Occasionally the connections corrode away on the cardboard cone,
otherwise check for broken track at audio IC and switch cleaner on Ext. Spr socket.

PT40/Lowe etc - Very low modulation, replace IC5 (BA402) front right of PCB.

Shogun - No channel display until mike keyed, replace Q401 (2SD667)

Rigs with Cybernet 134 PCB and dimmer knob - No channel display, replace Q251 on underside of channel selector PCB
(PTSW154AOX) with 2SC1318, 2SC2074, 2SD400 or 2SD471.

Ham International SSB radios - No TX or RX, check for 5.8v on pin 1 of PLL02A, if low then replace zener diode.

Team TRX40 - TX but no modulation, very common fault, the back of the mic socket is PCB mounted and the holes in it are far too
large. Re-solder the pins in the holes.

Planet 2000 - Received signal disappears after transmitting and only a hiss can be heard, re-tune power coils L8 and L7

Eprom Board - Any radio fitted with an eprom board which is stuck on one channel, try replacing 78L05 regulator on the eprom board.

Cybernet Board - Cybernet coil T4 can be replaced by L4, the yellow power coil at the rear of the radio. Remove the T4 can and fit
the L4 coil into the pair of holes (not the row of 3 holes).
To increase outgoing modulation remove R72 resistor next to the modulation pre-set and replace it with a wire link.
To increase incoming audio remove R57 resistor from the front of the board and replace with a wire link.

Uniden PC40 - This CB has 40 FM and 12 AM channels. If you look at the back of the PCB near the front end you will see a 10K
resistor. Removing this will give you the full 40 channels on AM. Note that on AM it will still only allow 1w output power.

Talk Back - For Superstar 360FM/Cobra 148GTL DX, disconnect one leg of D80 and insert a switch in series with it.
Superstar 3600/3900/Excaliber SSB/Galaxy 2100/Texas Star 2100, disconnect one leg of D90 and insert a switch in series with it.

Midland 77-099 - To increase RF output to 8w simply link the two legs of RV103 together (ignoring the centre leg) and re-tune the RF
output stages.
Very faint outgoing audio can be sorted by replacing Q306.

Fidelity 1000/Cheiza etc. - Transformer L6 gets damaged as a mounting screw is pushed into it.
As a temporary repair simply remove it and link diagonally opposite holes. The power
will be slightly down but performance will not be affected noticeably.

Cybernet Beta 3000 - Very low RX signal, RF gain control increases signal for
approximately 3/4 turn but final 1/4 turn reduces it again.

This can be caused by someone removing the solder link underneath the PCB as
shown in the sketch to the right.
Jesan KT5005 - (white) D11 which is located to the left of the output driver goes open
circuit, resulting in no TX.

Audioline/Uniden - Very low and distorted audio, remove the mic input PCB and locate
coil from earth pin to black wire (0v) as the coil may be open circuit. Either replace with
a similar one or simply fit a link wire.

The bottom of a Stud Mount - will screw into a normal 3/8" socket to adapt from a 3/8" to a SO239 socket.

A 2SC2086 - driver transistor can be replaced by a 2SC2314.

A 2SD471 or 2SD400 - transistor can be replaced with a 2SC2236.

A K40 Antenna - can have the cable replaced. Drill the solder out of the top of the mount where the cable goes in and the cable will
pull out. Simply feed back the shield line as for a PL259 and push it back in the hole then re-solder.

1307 Warning - The 1307 device in some burners/amplifiers are not the same as a 2SC1969. They are FETs and cannot be
replaced by an ordinary RF power transistor.

Cybernet/Fidelity 1000 - A microphone plug wired for Cybernet radios can be turned around to fit a Fidelity 1000 type set if you file
a second groove in the plastic part of the plug opposite the existing groove. Similarly a mic wired for a Fidelity 1000 can be adapted to
fit a cybernet radio.

Audioline - No incoming audio unless sides are pressed in, look for a dry joint on the audio IC. They are fixed to the side and
sometimes the solder moves and seperates due to a wrong mounting bracket which is slightly too wide being used.

Cybernet Board 134AOX - Problem with channels being all mixed up, look for dry joints on the channel selector switch where it fixes
to the main PCB. Sometimes the fixing nut that holds it to the front panel works loose and continual changing of channels causes
movement which over time damages the solder fixings. Re-solder solder connections on all pins or worst case link thin wires from all
pins directly to the PLL pins. Also don't forget to re-tighten the retaining nut on the front panel to stop it happening again.
Stuck on one channel, change the PLL IC LC7136/7.
If you use the hi/lo power switch for extra channels don't just tape the existing wires together, remove them and link the PCB pads next
to T4 which are numbered 32 and C6

Superstar 120 AM/FM - Stuck on TX, when you press the mic button you get RX. Try replacing the diode fitted next to the relay.

DNT Transit Type - Stuck on channel 9, no TX or RX. PLL IC 5121-01 has blown and if you can find a new one, needs replacing.

Albrect AE6199 (New radio) - Deviation pot (Modulation) is W7, TX Power out is W3.

CRT S MINI (New radio) - Board is 5288 RF7, W3 = Power out on FM, W6 = Low power adjust on AM, W7 = FM Deviation
(modulation), W4 = AM Modulation (Mic Gain). W2 = Normal squelch control. W1 = Auto Squelch

CRT 2000 (New radio) - W3 = TX Power, W2 = TX Power Meter, W5 = FM Deviation (Modulation)


Thats all for now.  Anything new will be added as and when I get chance. Thanks for viewing and I hope these pages have helped you
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