From bruce
Subject: Motorola MICOR and MITREX Mods

Here's everything I learned about Motorola MICOR and MITREX radios in

a week. The people who contributed information are:

 "Chris Terwilliger" From this experience I would suggest that you use the 800 number for parts.



The part number for the MITREX UHF manual is 68-81045E75, $11.55



As for channel elements, you can either send them in to one of the many

companies that do them, or you can buy crystals directly and solder

them in yourself. Companies that will make crystals are:



JAN Crystals, 1-800-526-9825, $11.00 per crystal.



Bomar, 1-800-526-3935, $15.00 per crystal or $25 to re-crystal your channel

element for you.



UHF and VHF MITREX elements should be KXN1086 for receive and KXN1088 for

transmit. The crystal companies know the specs for the elements, all they

want to know from you is the transmit and receive frequencies.



For the MICOR, but not the MITREX, there is a company called Channel

Element HQ, 1-800-237-9654. They maintain a very large stock of used

channel elements. They will sell you one on your frequency for $25.00

or $20.00 with trade in. The only catch is:do they have your

frequency? Amateur frequencies are commercial some where else in the

world, so they probably do.  All you need to give them is the model

number of the element, the frequency and, for receivers, if its high or

low injection. The advantage of them is there is no waiting for

re-crystaling.



This modification of a MITREX 440 to a 9600 full-duplex repeater

is from William Lyman, lyman


     I have successfully completed a assembling a 9600 fullduplex

data repeater. I used a Mitrex T44 with an MFJ 1270 TNC and Tapr

9600 baud modem with bit regen.

     This repeater in now in use at Bethany CT, Portland Ct, and

 Bridgeport Ct and they are all working GREAT.

     My first feeling was it wasn't going to work. I though that

internal desens would kill the receive.

     Here are some hits and suggestions for making this work Please

remember these mods for a Motorola Mitrex T44 UHF model.



     1) Be sure to get the elements temp comped! I didn't at first

and as it got used it drifted badly as the unit got hot.

     2) I maked 2 of the mods that MoAmps published for increasing

high frequency response at the limiter/Detector. If you are on a

fringe than this will really help.

     2a) Remove C240 a .0022 cap. This can be achieved by

physically grabbing it with pliers and breaking it away from the

PC board. Or you can remove the shield cover and unsolder it. I did

the later and that what I suggest.

     2b) Remove C451 a 220 cap between U403a pins 2 and 3.

     2c) Replace R231, 75.k resister with 2.2k resister

     3) Receive audio is (Det) is available on pin 11 of the

control cable connector.

     4) Lock receive element on. Please note this is for fullduplex

only this will cause unit receiver circuitry to be on all the time.

If you did this mod in simplex the modem would false by hearing you

only transmitted signal and would take longer time to lock.

     4a) Locate Q1 and add a jumper across the e and c junction

     5) The following are for transmitter mods

     5a) locate pin 15 of the interconnect board. This is not pin

15 where the control cable connects but pin 15 on the connector

that connects the interconnect PCB to the main PCB. Solder wire

from this connection to pin 1 on the backside of where the control

cable connects. With unit facing you (lock towards you) this will

be the top right most pin. You will see either a white jumper or

a coil (small) that goes from pin 1 to the rest of the circuitry.

Remove one side of this jumper.

     5b) Remove one side of each of the following caps.

C507,C508,C509. This will remove the splatter filter allowing you

to use Q503 and q504 to drive the element. You could drive the

element directly but I found that there was distortion when driving

the element hard. This also matches the Impedance on the Element.

     6) Xmit audio is now available on pin 1 on the control cable

connector.

     7) Rec/Xmit ant connections

     7a) On my unit the xmit connection to the ANT relay was hard

wired on to the final AMP. I didn't have any small coax so I left

the ANT relay in. My transmitter connection is at the existing ANT

connector. For the receive I unplugged (RCA JACK). Trace back from

ANT switch. I taped the jack and left in place. I drilled a hole

in the top cover over where the RCA jack plugged in. I then made

a cable with an RCA jack thus making this the Receiver connection.

I only drilled the hole in the cover because covers are easy to

come by if I make a mistake.

     8) Cable connections

     8a) The following connection to the motorola female connector

should be made.

pin 17 to pin 6 this is negative

pin 4 to pin 12 to + fused at 2 amps (Rec/Xmit enable)

pin 19 + fused at 20 Amp

pin 13 PTT

pin 1 xmit audio

pin 11 rec audio

     9) Summary

     9a) it is very important that the receive cable be of the best

quality. Remember it is VERY close to the Xmiter. When you adjust

the Xmiter follow the manual very close. You can't have any spurs.

     9b) I did experience some desense from the xmiter circuitry

in the range of .03 uV. I find that to be almost non existent.

    

     There might be other ways or mods. These have worked for me

in 3 installations. The mods are made so if you decide to resale

the radio. Just replace cover, install splatter caps, Install

jumper on pin 1, And remove jumper from pin 15 interconnect to pin

1 on cable connector. And resale.



     I am running the unit at 50 watts. It get warm, well very

warm. I would suggest that you place some blower fans blowing on

the heat sink. You could get a T74 (110 watt) unit and run it all

day at 50 watts, But they are very hard to come by.



          73's and good luck



This modification of a MICOR UHF to duplex mobile is from Jim Reese,

jreese


Why would you want a duplex mobile, you ask?  Once you've experienced it,

you'll never go back to jap-trac's.



This describes how to take a standard UHF micor mobile radio and make it

work as a full-duplex mobile radio.  Since Texas is high-in, low-out on UHF,

this also includes which cap changes are required to make the radio receive

below 445 MHz.



There are diagrams referenced in this text.  If you are unable to figure out

what to do without the diagrams, mail me at jreese
try to get you a copy of the diagrams.



Jim Reese

WD5IYT





             Conversion of Motorola MICOR UHF Radio

                    For Use as a Duplex Mobile





This  conversion  is  not  for  the  faint-hearted.  Make sure  you  are  very

familiar  with  the operation  of  the Micor radio before attempting this

conversion.  As with all  modifications  of this  type, insure that the radio is

operating correctly BEFORE any modifications are made.   It is much easier to

fix it before you hack it up.  Do not attempt this conversion without a service

manual.  You need the PC layouts and tune up instructions from the service

manual in order to perform the modification.





                     Useful Motorola Part Numbers



68-81015E70-H         Manual for UHF MICOR

KXN-1024            5ppm Channel Element for UHF MICOR

KXN-1029            2ppm Channel Element for UHF MICOR

KLN-6210A           PL Encode Reed

TLN-8381A           PL Decode Reed

66-84690C01          Contact Removal Tool for MICOR plugs

TKN-6458A           Large Fuse Holder for Primary Power (40A)





                      Crystal Ordering Information



When  ordering crystals, specify the KXN-1024A channel element number.  Always

order  the crystal on the RECEIVE frequency.  If your radio will be a high

transmit unit, the crystal  will be  LOW  side injection.  For low transmit

radios, order the crystals on HIGH  side  injection. This will flip the transmit

offset to the other direction.





                        Conversion Instructions



                              Step 1:



Make  sure that the radio is operating properly by tuning it up with one of your

crystals  before any modifications are made.  If you are using the radio as a

high transmit unit, you must  make the capacitor changes in step 2 for the radio

to work properly.



                              Step 2:



If  your  radio  will be receiving below 445 MHz, change C117 to 27pF,  C119  to

39pF,  and C125 to 12pF on the receiver board.  This is not necessary if the

radio will be receiving  above 445 MHz.



                              Step 3:



You  must make some modifications to the control board and the receiver

audio/squelch  board in  order  to  make the radio full duplex.  First, remove

JU-905 on  the  control  board.   Next, jump pins 1 and 4 of the audio squelch

board.  On the later version audio squelch board,  there is a place for a jumper

(JU-202), on earlier units, just make the jump with wire wrap wire.



Add  capacitors at the following points on the audio squelch board.  Add a 100pF

cap  between P903-5 and P903-6.  On IC-201, add 15pF caps between pins 3 and 4,

and between pins 3  and 5.   Add  100pF  caps between pins 6, 7, 11, and 13 of

IC-201 and ground.   On  IC-202,  add 15pF caps between 5 and 9, 5 and 13, and a

33pF cap between 5 and 15. This makes the board less susceptible to RF.  Keep

the leads on these caps as short as possible.



                              Step 4:



Carefully remove the front casting from the chassis.  This is done by removing

the four screws top  and  bottom as well as two screws on the control head plug.

This is kind of tricky,  so  be careful to remember how you got it apart so you

can re-assemble it later.



Examine  the  Power Amplifier section of the radio and notice the  miniature

connector  which connects  the  output  of the PA to the circulator.  Unplug

this  connector  from  the  circulator using a needle nose plier or hemostat.



Turn over the radio and remove the power control board.  This will expose the

top plate of  the circulator.   Remove  the circulator by carefully removing the

sensing wires which  connect  to the  power  control  board and the two screws

which hold the circulator in.  You  will  have  to unplug  the  receive antenna

coax from the preselector unit in order to  remove  the  circulator. Set the

circulator aside for later modification.



                              Step 5:



Mount a BNC chassis mount connector on the top side of the front casting on the

side  opposite from  where the lock is located.  This will be the receive

antenna connection.  Be very  careful to locate this connector so that it does

not hinder the operation of the latch mechanism.  Attach a  small coax to this

connector and route it to the receive antenna jack on the  preselector  unit.

Drill  a  hole in the front of the radio chassis to pass the coax.  This will be

obvious  once  you have examined the unit with the front casting removed.



                              Step 6:



This  is  the  toughest part of the conversion, the circulator  modification.

Remove  the  cover from the circulator unit.  You will notice that there is a

circulator, an output filter, the  antenna switch, and the circulator reject

load.  There are three trimmer caps, only one of which has  an access  hole  in

the top plate.  Measure and drill the top cover so that you  have  access  to

all three  trimmers from the outside.  This is necessary because the cover

affects the tuning of  the circulator.  After drilling the cover, set it aside.



You  must  now  remove  the  antenna  relay.  This is a small relay  on  the

right  side  of  the circulator.   The small dark red or green rectangular unit

with a wire coming from the relay  is the reject load for the circulator.  This

is a ceramic 75W 50 Ohm resistor.  The relay  switches the  output  port of the

circulator between the receiver and the reject load.   Be  EXTREMELY CAREFUL

when soldering on the reject load, as the top terminal can break off of the

ceramic very  easily.  I suggest cutting the wire from the relay, removing the

relay, and then  removing the  wire from the load resistor.  Once the relay is

removed, wire the dummy load back to  the output port of the circulator which is

on the common side of the relay.  Refer to the manual for the  circuit. The

easiest way to accomplish this is with a small piece of teflon  coax  (RG-188).

Run  from  the circulator port to the reject load.  You can solder to the

circulator case  for  the shield  on  the load end of the coax. Replace the

cover on the circulator and reinstall  it  in  the radio.





                         Tuning Instructions



Before tuning, disable the receiver AFC by soldering a wire from the "AFC OFF"

trace on the receiver  board  to ground.  The procedure for disabling the AFC is

described  in  the  receiver tuning instructions section of the service manual.



Tune  the  radio per the Motorola manual.  Once you have achieved this, you need

to  tune  the circulator.  The following procedure should be followed:



Remove the power control board, and power the radio with a supply having a

current meter.



Attach  a  jumper  or  clip  lead  from feedthrough C527 on  the  Controlled

Stage  in  the  PA compartment  and  feedthrough  C536 on the driver stage in

the  PA  compartment.   This  will force the radio to maximum power output.



Key the transmitter and tune the three circulator capacitors for maximum power

output.



Reinstall  the power control board, and preset the drive limit pot fully

counter-clockwise.   Set the power set pot to the desired power output level.



Key  the  transmitter and tune the center circulator capacitor (the only one

accessible  from  the top  of  the  power  control board) for minimum current

draw.  You  should  be  able  to  make several Amps difference without affecting

the power output.



Turn the drive limit pot 1/4 turn clockwise, or until power just starts to fall

off.



That's  it.  Remember to always set the receive frequency first when setting

frequency, as  this affects  the  transmitter  also.   Set the transmitter with

the offset trimmer  coil  on  the  exciter board.  Make sure that you have

adequate cooling space around the PA heat sink fins when the radio is installed.

The Micor PA is not easy to fix, and when it blows, it blows big.

--

     Jim Reese, WD5IYT            | "Real Texans never refer to trouble

  jreese


This modification of a MICOR UHF to repeater service is from Jim Reese,

jreese


Instructions for Conversion of Motorola UHF Micor to Repeater Service





This modification is not for the faint-hearted.  Be sure you are very

comfortable with the operation of the MICOR radio before you attempt this

modification.  A thorough understanding of the way the MICOR radio and control

system works is absolutely essential for the success of this conversion.





                        Modification Notes



Whenever "Molex Pin x" is mentioned, it refers to the Armadillo Standard

connector.  This is a small, 9 pin Molex connector which serves as the

interface for all of the Armadillo radios.  Use a Female connector on the

radio end.  The standard pinout of the connector is:



      1 - Ground

      2 - Receive Audio Output

      3 - n/c

      4 - Transmit Audio Input

      5 - COS Output

      6 - PTT Input

      7 - n/c

      8 - PL Decoder Output (Sense)

      9 - PL Select Input



The COS output and PTT input are open-collector to ground signals.  Pin 8 goes

to +9.6 V when PL is decoded.  Pin 9 is ground for PL, open for Carrier.



These modifications allow "PL and Squelch" operation.  This means that when in

PL, the normal squelch circuit still operates.  This avoids long noise bursts

upon unkeying.



If using an Advanced Computer Controls controller, the signal at pin 8 is run

to the "PL Sense input" on the controller.  It will drive this input directly.



Order the crystal on the repeater RECEIVE frequency.  You must specify HIGH

SIDE INJECTION.  If you do not order a high side crystal, the transmit offset

will be 5 MHz above the receive frequency, instead of 5 MHz below.  I

recommend sending the channel element to the crystal manufacturer for

temperature-0 compensation.  Use a KXN-1024 element for 5ppm accuracy, or use a

KXN-1029 element for 2ppm accuracy.  Disable the receiver AFC by jumping the

appropriate pin of the channel element to ground.







                 List of Tables and Illustrations



There are several illustrations which are detailed below.  Refer to them as

needed when modifying or constructing pieces of this project.



Table 1:This is a complete hookup chart for the control head plug and

interface board.



Figure 1:Schematic of control head plug, with simple diagram.

Figure 2:Board Layout of audio squelch board detailing added capacitors.

Figure 3:Detail of circulator unit showing location of major components.

Figure 4:Schematic of circulator unit before modification.

Figure 5:Schematic of circulator unit after modification.

Figure 6:Schematic of interface board.

Figure 7:Rough layout of interface board.





                   Useful Motorola Part Numbers





68-81015E70-H     Manual for UHF MICOR

KXN-1024          5ppm Channel Element for UHF MICOR

KXN-1029          2ppm Channel Element for UHF MICOR

KLN-6210A         PL Encode Reed

TLN-8381A         PL Decode Reed

01-84307A89       Empty Control Head Plug less cable, complete with pins

66-84690C01       Contact Removal Tool for MICOR plugs

TKN-6458A         Large Fuse Holder for Primary Power (40A)





            Step-By-Step Instructions for Modification





Step 1:Make sure that the radio operates properly BEFORE any modifications

are done.  If there are problems with the radio, they will be easier to fix

before the mods are done.



Step 2:If you are satisfied with the operation of the radio, construct the

control head plug per figure 1 and table 1.  Use miniature pots and switches

inside the control head plug. It is rather tight inside, so be careful to

check that the connector will re-assemble before you drill it up.  After you

have constructed the connector, make the following connections inside the

radio:Jump control head pins 3, 8, and 22 to "A+" on the control board.  Jump

pins 9, 11, and 17 to ground on the control board.  Next locate the two

feedthrough caps which power the Transmitter Power Amplifier.  They are just

to the left of the control head plug on the bottom side of the radio.  One

will have a red wire, and the other a black wire.  Jump from the feedthrough

with the red wire to the "A+" trace on the control board.  Jump from the

feedthrough with the black wire to the ground trace on the control board.

There is a reverse polarity protection diode on the control board which can be

used to make these connections.  Next, plug your control head plug into the

radio and verify proper operation with the new control arrangement.  If there

are problems here, troubleshoot them NOW.  Do not wait until later, as you may

be chasing more than one problem.



Step 3:You must make some modifications to the control board and the receiver

audio/squelch board in order to make the radio full duplex and to make

preparations for the interface board.  First, remove JU-905 on the control

board.  Then, jump the F1 channel element to ground as described in the

Motorola manual.  Next, jump pins 1 and 4 of the audio squelch board.  On the

later version audio squelch board, there is a place for a jumper (JU-202), on

earlier units, just make the jump with wire wrap wire.  Next, remove a jumper

on the audio squelch board which goes from pin 3 of the PL decoder to IC-202

pin 8. This is near the pins which the PL board plugs into.  Next, ring from

pin 3 of the PL decoder to pin 11 of the audio squelch board with an ohmmeter.

There should be continuity here.  If not, add a jumper.  The later boards have

a trace from pin 3 of PL to pin 11 of audio squelch, on earlier boards, pin 11

is unused, and you should jump from PL decoder 3 to audio squelch 11 with some

wire wrap wire.  Add 15pF capacitors between the following pins on the two

chips on the audio squelch board.  Figure 2 details the location of these

caps.  On IC-201, add a cap between pin 3 and 4, and between pin 3 and 5.  On

IC-202, add caps between 5 and 9, 5 and 13, and two caps between 5 and 15.

This makes the board less susceptible to RF.



Step 4:Next, carefully remove the front casting from the chassis.  This is

done by removing the four screws top and bottom as well as two screws on the

control head plug.  This is kind of tricky, so be careful to remember how you

got it apart so you can re-assemble it later.  Next, examine the Power

Amplifier section of the radio and notice the miniature connector which

connects the output of the PA to the circulator.  Unplug this connector from

the circulator using a needle nose plier or hemostat.  Next, turn over the

radio and remove the power control board.  This will expose the top plate of

the circulator.  Remove the circulator by carefully removing the sensing wires

which connect to the power control board and the two screws which hold the

circulator in.  You will have to unplug the receive antenna coax from the

preselector unit in order to remove the circulator.  Set the circulator aside

for later modification.



Step 5:Procure a BNC chassis mount connector for a receive antenna jack.

Mount this connector on the top side of the front casting on the side opposite

from where the lock is located.  Be very careful to locate this connector so

that it does not hinder the operation of the latch mechanism.  Attach a small

coax to this connector and route it to the receive antenna jack on the

preselector unit.  Drill a hole in the front of the radio chassis to pass the

coax.  This will be obvious once you have examined the unit with the front

casting removed.



Step 6:This is the toughest part of the conversion, the circulator

modification. Figures 3, 4, and 5 detail the conversions.  Remove the cover

from the circulator unit.  You will notice that there is a circulator, an

output filter, the antenna switch, and the circulator reject load.  There are

three trimmer caps, only one of which has an access hole in the top plate.

Measure and drill the top cover so that you have access to all three trimmers

from the outside.  This is necessary because the cover affects the tuning of

the circulator.  After drilling the cover, set it aside.  You must now remove

the antenna relay.  This is a small relay on the right side of the circulator.

The small dark red rectangular unit with a wire coming from the relay is the

reject load for the circulator.  The relay switches the output port of the

circulator between the receiver and the reject load.  You must remove the

relay and wire the dummy load back to the output port of the circulator which

is on the common side of the relay.  Refer to the diagram for the circuit. The

easiest way to accomplish this is with a small piece of teflon coax (RG-188).

Run from the circulator port to the reject load.  You can solder to the

circulator case for the shield on the load end of the coax. Replace the cover

on the circulator and reinstall it in the radio.





Step 7:Construct the interface board using the schematic and board layout in

the packet.  Install this board on the three unused mounting tabs near the

rear center of the radio.  These tabs are above the control board.  Wire the

board up as described in table 1.  At this point, the radio will be operating

full duplex, and you should be able to put the radio in PL by flipping the

switch on the control head plug to the PL position.  Verify that you have +9.6

volts at the 9 pin molex connector PL SENSE pin when the correct PL code is

being sent.  Also verify correct receive audio gating and COS action.





                       Tune Up Instructions





Tune the radio per the Motorola manual.  Once you have achieved this, you need

to tune the circulator.  The following procedure should be followed:



Step 1:Remove the power control board, and power the radio with a supply

having a current meter.



Step 2:Attach a jumper or clip lead from feedthrough C527 on the Controlled

Stage in the PA compartment and feedthrough C536 on the driver stage in the PA

compartment.  This will force the radio to maximum power output.



Step 3:Key the transmitter and tune the three circulator capacitors for

maximum power output.



Step 4:Reinstall the power control board, and preset the drive limit pot

fully counter-clockwise.  Set the power set pot to the desired power output

level.  I recommend no more than 50W out for a 75W radio, and no more than 60W

out for a 100W radio.  The 25 and 45W radios are rated continuous duty at 25W

output.  



Step 5:Key the transmitter and tune the center circulator capacitor (the only

one accessible from the top of the power control board) for minimum current

draw.  You should be able to make several Amps difference without affecting

the power output.



Step 6:Turn the drive limit pot 1/4 turn clockwise.



That's it.  you are now ready for major repeating action.  Remember to always

set the receive frequency first when setting frequency, as this affects the

transmitter also.  Set the transmitter with the offset trimmer coil on the

exciter board.  Make sure that you have adequate forced air cooling on the PA

at all times during operation.  The Micor PA is not easy to fix, and when it

blows, it blows big.



This modification of a MICOR VHF to repeater service is from Jim Reese,

jreese


Instructions for Conversion of Motorola VHF Micor to Repeater Service





This modification is not for the faint-hearted.  Be sure you are very

comfortable with the operation of the MICOR radio before you attempt this

modification.  A thorough understanding of the way the MICOR radio and control

system works is absolutely essential for the success of this conversion.





                        Modification Notes



This modification was developed for radios having receiver RF/IF board series

TLD8270A; audio/squelch models TLN4310A-2 thru TLN4310A-5; and exciter models

TLD8261A, TLD8262A, TLD8261B, or TLD8262B.  If your radio differs from these

part numbers, all or part of this modification may be different from the

descriptions.  Use your judgement to alter these instructions as necessary.

                                                                    

Whenever "Molex Pin x" is mentioned, it refers to the Armadillo Standard

connector.  This is a small, 9 pin Molex connector which serves as the

interface for all of the Armadillo radios.  Use a Female connector on the

radio end.  The standard pinout of the connector is:



    1 - Ground

    2 - Receive Audio Output

    3 - n/c

    4 - Transmit Audio Input

    5 - COS Output

    6 - PTT Input

    7 - n/c

    8 - PL Decoder Output (Sense)

    9 - PL Select Input



The COS output and PTT input are open-collector to ground signals.  Pin 8 goes

to +9.6 V when PL is decoded.  Pin 9 is ground for PL, open for Carrier.



These modifications allow "PL and Squelch" operation.  This means that when in

PL, the normal squelch circuit still operates.  This avoids long noise bursts

upon unkeying.



If using an Advanced Computer Controls, S-Com or other commercial controller

which requires an active high PL sense signal, the signal at pin 8 can be

attached to the "PL Sense input" on the controller .  It will drive this input

directly.  On the S-Com controller, the pull up resistor on the PL sense input

must be removed for proper operation.





                 List of Tables and Illustrations



There are several illustrations which are detailed below.  Refer to them as

needed when modifying or constructing pieces of this project.



Table 1:This is a complete hookup chart for the control head plug and

interface board.



Figure 1: Schematic of control head plug, with simple diagram.

Figure 2: Board Layout of audio squelch board detailing added capacitors.

Figure 3: Schematic of interface board.

Figure 4: Rough layout of interface board.





                   Useful Motorola Part Numbers





68-81008E40-D     Manual for VHF MICOR

K1007A            TX Channel Element for VHF MICOR

K1005A            RX Channel Element for VHF MICOR

KLN-6210A         PL Encode Reed

TLN-8381A         PL Decode Reed

01-84307A89       Empty Control Head Plug less cable, complete with pins

66-84690C01       Contact Removal Tool for MICOR plugs

TKN-6458A         Large Fuse Holder for Primary Power (40A)





            Step-By-Step Instructions for Modification





Step 1:Make sure that the radio operates properly BEFORE any modifications

are done.  If there are problems with the radio, they will be easier to fix

before the mods are done.



Step 2:If you are satisfied with the operation of the radio, construct the

control head plug per figure 1 and table 1.  Use miniature pots and switches

inside the control head plug. It is rather tight inside, so be careful to

check that the connector will re-assemble before you drill it up.  After you

have constructed the connector, make the following connections inside the

control head plug:Jump control head pins 3, 8, and 22 to +12 V.  Jump pins 9,

11, and 17 to ground.  Plug the newly constructed control head plug into the

radio and verify proper operation with the new control arrangement.  If there

are problems here, troubleshoot them NOW.  Do not wait until later, as you may

be chasing more than one problem.



Step 3:There are some modifications required on the control board and the

receiver audio/squelch board in order to make the radio full duplex and to

make preparations for the interface board.  Remove CR201 on the audio/squelch

board.  Then, jump the F1 channel element to ground as described in the

Motorola manual.  Next, jump pins 1 and 4 of the audio squelch board.  On the

later version audio squelch board, there is a place for a jumper (JU-202), on

earlier units, just make the jump with wire wrap wire.  Next, remove a jumper

on the audio squelch board which goes from pin 3 of the PL decoder to IC-202

pin 8. This is near the pins which the PL board plugs into.  Check for

continuity from pin 3 of the PL decoder to pin 11 of the audio squelch board

with an ohmmeter.  If there is not continuity, add a jumper.  The later boards

have a trace from pin 3 of PL to pin 11 of audio squelch, on earlier boards,

pin 11 is unused, and you should jump from PL decoder 3 to audio squelch 11

with some wire wrap wire.  Add 15pF capacitors between the following pins on

the two chips on the audio squelch board.  Figure 2 details the location of

these caps.  On IC-201, add a cap between pin 3 and 4, and between pin 3 and

5.  On IC-202, add caps between 5 and 9, 5 and 13, and two caps between 5 and

15. This makes the board less susceptible to RF.



Step 4:Next, carefully remove the front casting from the chassis.  This is

done by removing the four screws top and bottom as well as two screws on the

control head plug.  This is kind of tricky, so be careful to remember how you

got it apart so you can re-assemble it later.  You will expose the antenna

relay with its two associated coax cables running to the transmitter and

receiver.  Unplug the receive coax from the antenna relay.





Step 5:Procure a BNC chassis mount connector for a receive antenna jack.

Mount this connector on the top side curved surface of the front casting on

the side opposite from where the lock is located.  Be very careful to locate

this connector so that it does not hinder the operation of the latch

mechanism.  Attach the receive coax to this connector routing the cable

through a hole which you will drill in the front of the radio chassis.  The

method will be obvious once you have examined the unit with the front casting

removed.





Step 6:Construct the interface board using the schematic and board layout in

the packet.  Install this board on the three unused mounting tabs near the

rear center of the radio.  These tabs are above the control board.  Wire the

board up as described in table 1.  At this point, the radio will be operating

full duplex, and you should be able to put the radio in PL by flipping the

switch on the control head plug to the PL position.  Verify that you have +9.6

volts at the 9 pin molex connector PL SENSE pin when the correct PL code is

being sent.  Also verify correct receive audio gating and COS action.





                       Tune Up Instructions



Tune the transmitter and receiver per the Motorola manual.  Follow the

procedures exactly.



Adjust the power set for the desired power output.  I reccommend no more than

60 Watts for 110 Watt radios, 40 Watts for 60 Watt Radios, and 30 Watts for 45

Watt Radios.



That's it.  you are now ready for major repeating action. Make sure that you

have adequate forced air cooling on the PA at all times during operation.  The

Micor PA is not easy to fix, and when it blows, it blows big.