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CB Radio History from its early days
CB Radio Repairers in the UK
This page is written to help you with the legendary Maxcom 4E and such radios like the Midland 2001, Sirtel Searcher, Maxcom Apollo
16E and so on. A lot of the information can be found on the General Help pages but this page brings it all together in one easy view.
The Maxcom type board was a middle of the range quality board and the radios were pretty basic and small for the time with the
exception of the Midland 4001 which was the top of the range legal UK27/81 model.
Maxcom/Midland Rigs - Often suffer from "Spurious emissions"(good word that) during TX which can easily be seen on an
Oscilloscope. Symptoms include sending SWR meters wild and kicking out a seemingly good signal but only being heard locally. In
bad cases it can also send frequency counters haywire as more than one frequency is being transmitted. Somewhere along the radio
spectrum your voice will be heard like your actually on that channel.(in fact you are) The effect seldom causes any serious problems
with your equipment and the cause is normally mal-adjustment of the RF can nearest the Left hand side of the chassis (looking at the
component side with front towards you)

Replace The existing ceramic filter with a PR Goolage 1K crystal filter. Remove C110 (27pf) and R189 (390R) and re-tune T8.

Sensitivity - Can be improved by de-soldering one leg of C207 (but leave it in place)

Power Output - Can be increased by changing R147 to 1ohm.

Lazy Needle - Can be cured by changing R128 (4k7) to 1k.  Cut brown wire to signal meter and insert a 270R resistor.  Connect a
germanium diode from the other tag of the S meter to the 270R resistor. (The diode cathode band should be at the non-meter end of
the resistor) Adjust power meter to 4w with RV103.

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

Audio IC - The audio IC is a KIA7205CP which is almost the same as a TA7205AP bit it is in a smaller package. A standard TA7205AP
audio IC will not fit in most of these radios due to the pre-formed pressed fixing. If you are desperate and don't mind bodging the
repair you can use a TA7205AP on the track side of the board making sure it does not short out on any of the existing track parts. Do
this only if you have no other choice.
LED Display - Digit out - Well, unless you are pretty handy with a soldering
iron it is best not to attempt this. If you are and you have a decent soldering iron
then it is daunting looking at what you need to do but if you take it in stages
then you can manage it. Taking it for granted you have already removed the
outer casing you need to remove the front panel and remove the channel
selector holding nut. Then remove the screws holding the chassis front and tilt
down. Push the channel selector spine loosening it from the front chassis then
remove the two screws holding the LED channel display board and pull away
from the front chassis. All those wires! but if you look closely the wires to the left
hand side are mirrored on the right hand side. Write the positions of these wires
on a scrap piece of paper so you know how they go back. Once these are off
then de-solder the display and remove from the board. Re-fitting is the reverse

but take note of the thick orange which comes from the on/off switch and covers
two pins.
Make sure you have the LED Display the correct way up and be
careful not to short out any of the links
when re-soldering the wires otherwise
the display will go haywire. Re-assemble then power up to make sure the display
shows as it should.
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MAXCOM 21E
UK/MID SWITCH WIRING
LC7132 PLL IC WIRING
Fitting a mid block - Prepare the LC7132 PLL IC as per the diagram
on the right. There are different ways of doing this but this is the way I
do it mainly because it takes up the least amount of space and looks
tidy. Solder the 5 free pins
12, 13, 18, 19, 20 directly on to the
corresponding pins of the
LC7136/7 and then solder the flying 8 wires
(I use ribbon cable) to the channel selector board as per the diagrams
below. Cut the track to isolate pin
14 of the LC 7136/7 and from the
track side of this cut solder a wire to the centre connection (common)
of your selected switch. Solder a piece of wire from pin 14 and take it
to one side of the switch which will be the UK40 side. The wire you
soldered on the LC7132 (yellow in the pic) goes to the remaining pin
on your switch. You can solder in a
22pf capacitor from one leg of the  
xtal to eth, which will bring the frequency a bit closer on Mid and UK
(see diagram) Next is to tune the radio making sure the radio covers
the full frequency from ch 1 mid to ch 40 UK on both RX and TX, also

make sure the power level is also pretty even on both 'blocks'.
DISCLAIMER
AS THIS RADIO HAS BEEN EXPANDED IT WILL NO LONGER BE TYPE APPROVED AND WILL BE ILLEGAL TO USE JUST THE SAME AS ANY NON
STANDARD CHANNELS BEING ADDED TO "ANY" CB RADIO. I DO NOT CONDONE THE ADAPTION OR USE OF ILLEGALLY CONVERTED RADIOS
AND THIS INFORMATION IS FOR EDUCATIONAL PURPOSES ONLY.
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