Motorola SyntorX 2-Meter Conversion, Programming and Tune-up

John West, KB0ONB

(Read: What's so great about the Motorola SyntorX?)


(Most of these tools can be substituted. The job is just a lot easier with them.)

Motorola key (I have them for sale cheap if you need one.)

Torx T15 bit and driver

Dremel with grinding disk

Medium small flat blade tweaking screwdriver


Heatsink compound

7/32 socket and driver (if the bottom plate doesn't have Torx head screws.)


(Some you'll need, some you can fake, some you can do better than, some you might just ignore. You decide. All must be good up to 150 MHz. )

100 to 200W dummy load/Watt meter (or dummy load and in-line Watt meter)

Freq counter

Signal generator

Deviation meter


Clean the radio, cables and accessories. Ensure you have :

radio chassis

control/power cable

control head



Hangup box, if needed

The heavy red lead should have an inline 40 amp, 32 Volt fuse and holder.

The green wire and the orange wire coming from the control head should each have an inline fuse of 7.5 Amps, 32 Volt rating and holder.


1. Remove mounting plate (if attached.)

2. Remove bottom plate (bare metal plate.)

3. Remove circuit bd located in opposite corner from ant jack. (Unplug all wires attached below. Discard the removed bd.)

4. Do a careful bd level visual inspection (including beneath hinged bd and the Power Amp bd on the flip side of the chassis.)

5. Press lightly on socket ICs with thumb to ensure proper seating.

6. Ensure radio is equipped with memory code plug. (Black plastic module w/orange stripe on top, beside 40 pin IC.)

7. Ensure mounting screws are snug on all heatsunk transistors. (Don't over tighten!)

8. Ensure antenna jack mounting nut is snug.

9. Ensure all ribbon connectors and RCA jacks are snug.


See Appendix A for cable mods

1. Plug heavy black cable conector block into radio chassis (screw down, solid finger tight)

2. Plug small black connector and small blue connector into control head. (the connectors only fit one way and each in only one jack.

3. Plug microphone and speaker into control head.

4. Attach heavy black wire to power source DC ground

5. Ensure conytrol head power sw is "off."

6. Attach fused heavy red wire to +12 to +14V power source capable of delivering 30 Amps. (I use an RV battery with a trickle charger.)

7. Attach fused orange and green wires to + power source as well.

8. Connect antenna jack to 100W+ dummy load/power meter.


At this point I power up the radio at the control head, turn to ch 1, turn the squelch open and the volume up a bit, and listen for audio output on the speaker (carefully, it gets loud.) Then I momentarily key the mike and watch for RF power output on the Wattmeter.

This is to verify radio functionality before modification. Key up only for an instant, and always into a dummy load. Note the power output. It's typically around 100 Watts, (on my model rigs) but it may have been adjusted to a lower level, or else the SWR on your dummy load may be high enough to cause the rig's SWR sensor to reduce power. In any event, if it isn't over 40 Watts or so there's a problem.

REMEMBER, whatever frequency the rig is on when you first get it probably isn't yours, and even dummy loads can radiate! I have a frequency code plug handy that I swap with the stock one for this test. It contains my amateur band test and alignment freqs. But I still keep the key down time short and use the dummy load.

If you heard the roaring noise on the speaker and saw deflection on the Watt meter, good. If not, bad. Recheck your connections. If you still have problems, contact a good RF tech. DON'T do the mods until your rig is working. The mods won't fix whatever's wrong, and will introduce several more error possibilities. Service people *always* prefer to troubleshoot unmodified gear.


Note: A specific and detailed reference list of all the mods I make on my rigs is in Appendix A at the end of this writeup. Your wiring mods may vary.

Reprogram the EEPROM with the freqs of your choice.

Note: Programming info is found in Appendix B at the end of this doc.


WITH POWER OFF, remove the four screws holding the lid on the VCO. (That's the lid with the sticker that says "Caution, Do not field adjust.") Don't worry. The sticker refers to the preselector screws the sticker's arrows are pointing at, not the VCOs, and we don't adjust the preselector until later. :-)

With the lid removed you will see two rows of tiny circuit bd pads with small wires connecting some of the pads in the row. Find any breaks in the wire between the pads and grind through the conformal coating to the wire and pad surfaces at the break and solder the breaks back together. Use a good iron. The substrate is ceramic and draws the heat rapidly away from the solder joint. When you're done you should have two complete strings of pads.

This mod lowers the center frequencies of the xmit and receive VCOs and makes operation on 2 meters more reliable in cold weather. Replace the lid. Make sure it's snug. If it's loose, microphonics may result. You can actually talk (yell,) directly into a loose VCO lid and be heard and understood on another rig, just in case you lose your mike. :-)


Connect a signal generator to the antenna jack. Set it on the receive frequency programmed into the rig that is closest to 146 MHz, the center of the 2 meter ham band. Do all receiver tuning on this frequency. Before adjusting the preselectors I usually look for a signal at about -110 dBm with my radios equipped with receive preamps.

Then turn off radio power long enough to loosen the locknuts on the string of preselector screws.

Switching the power off on the control head does *not* remove power from the heavy red cable to the RF and AF power amp circuits. Either be careful or remove power from the heavy red cable.

Then with the sig gen set to the lowest receiveable sig strength adjust the preselector screw closest to the side of the radio for lowest noise. Then work your way through the row of tuning screws until you get to the other end. Most, but possibly not all, will be screwed in, not out. But double check. Reduce the signal power from the generator enough to keep the signal noisy as you adjust. Repeat until satisfied.

Fortunately, the 2 meter band is only 4 MHz wide and the rig is very broadbanded, so it isn't necessary to use a spectrum analyzer sweep of the band as you adjust the preselectors, just tune for a peak at 146 MHz. It works well for me.

With a 1kHz audio tone on the signal I still hear a reasonably good tone mixed with the noise at -130 dBm by the time I'm done. Carefully retighten the locknuts, then recheck the signal. That will do it for the receiver.

Note: Another receiver tuning methodology may be found in Appendix C.

Now comes the transmitter.

The hinged flip-up circuit bd has trim pots to adjust several different things. We will be adjusting the output power level first. This adjustment must be done with a storage battery powering the rig, or with a good 30 to 40 Amp power supply set to a nominal 13.8 Volts. When the RF power is cranked up the current draw could reach that level. These radios are brutes when cranked up. Or you can just as easily back them down to 50 Watts. Lots of options.

Adjustments on the flip up circuit bd (Common Circuits bd):

R911 High power set

R983 Low power set

R516 Deviation compensation (mic and data)

R517 mic audio deviation only

R939 RF current limiting

Don't adjust anything you can't reset to the original point, and don't adjust anything you aren't equipped to measure and set correctly. When in doubt, the standard settings are usually just fine.

The hinged board, (common circuits board,) cannot be left swung up for extended periods of time. The long screw with the metal and the fiber washers that's located in the slotted hole in this board holds a heatsink firmly against the radio's chassis to keep three voltage regulating transistors cool. You have no more that a few minutes to make your adjustments before the board could overheat and everything goes haywire. Make your adjustments, then screw the bd right back down. I usually put heatsink compound on that thermal butting connection when I'm ready to button the rig back up.

Back to R911. If your power supply is stiff enough and set to 14 Volts or so, be aware that the High power set adjustment might give you as much as 200 Watts. All the radios I've adjusted have hit 150 Watts at a minimum, and that was with only 12 Volts or so applied. The higher automotive type voltages to 14V can make a substantial difference when this power limiting is opened up. Choose your dummy load accordingly. I've seen one of these radios set at about 2/3 power melt amobile antenna coil, and the top of the whip fell over. Don't let it happen to you.

I have yet to blow out the RF finals on one of these radios, or even see any that were. And these radios have broadband RF amp stages so no xmit retuning is necessary for the amateur band. You will need no outboard "brick" RF amplifier with these rigs.

Other things you can check and set if you are properly equipped are the deviation and the reference frequency. See Appendix A below.


Appendix A

DETAILS OF MODS and tuning synopsis for Dual power Syntorx



* r means remove. r&r means remove and replace *

Black connector-------------------------------------------------------------------------

1 yellow r&r with the yellow wire from 18 on grn con

2 black (hang up bx) *

3 orange *

4 blk/blue r from pin 7 of green con and install here

5 Violet * not used

6 Lt green *

7 blk/grey *

8 *

9 blk/violet r&r with blk/violet from 13 on grn con

10 Shield on rd cable w/brn *

11 blk/yellow *

12 green power * Has 7.5 Amp in line fuse

13 orange power * Has 1.5 Amp in line fuse

14 blk/red *

15 green (hang up bx) r from 19 on grn con, install here

16 blk/very dark brn r and r with same from pin 15 on grn con

17 brn from red coax cable *

18 *

19 *

20 blk/grn r&r with blk/grn from pin 21 on grn con

21 cable shield r&r with shield from pin 20 on grn con

22 blk/dark orange *

Blue connector----------------------------------------------------------------------------

1 grey *

2 *

3 blk *

4 white/blk *

5 remove

6 red/green r&r with red/grn from pin 4 on yellow con

7 white/orange *

8 white/grey r&r with white/grey from pin 10 on grn con (gnd for scan)

9 white/red *

10 white/blue * not used

11 blue *

12 *

13 *

14 white/brn *

15 *

16 *

17 *

18 *

19 white/grn * not used

20 *

21 *

22 white *

Note: The heavy red lead from the J1 connector is for the RF Power amp +12V lead (13.8V) and must have a 40 Amp in-line fuse at the battery (+). In many new cars, the heavy black lead (ground) MUST go to the vehicle chassis near the radio, not to battery (-). It's best to do that on any car. It helps avoid stray RF on the coax and such.


Add two switches, one for a 32 channel mod, and one for dual power mod (or scan mod) to the control head. (I use mini SPST toggles mounted in 1/4 inch holes where ther's room on either side of the clamshell control head.

Cut the red wire in the control head and solder the two ends, one to the center pin and one to the top pin of the right side mounted add-on switch for the 32 ch mod. Flip sw DOWN for ch 1-16, UP for ch 17-32.

Wire the center pin of the dual power switch mounted on the left side of the clamshell head to gnd (pin 10 on black con socket.) Wire the top pin of the dual power switch to pin 6 of the socket of the blue con.

For scan enable/disable, wire pin 8 of the blue con socket to the bottom pin of the left side sw. Wire the middle pin on the switch to gnd (Pin 9 on the socket of the black con.) Flip left sw Up to enable channel scan, Down to disable. It only scans if the channel you're on has a scan list programmed in. Note: With the clamshell head you cannot tell which channel is being scanned.


Remove the HLN4270B add on bd and the pin plug wires going to the personality bd.

VCO circuit

Grind a solderable surface on the capacitor pad strings for both Xmit

and Receive VCOs where the pad jumpers have been cut.

Add new jumpers between the pads. Clean with alcohol and Qtip.

Personality bd.

Remove JU1 to help stop scan mode. Remove JU2 to disable Data Burst output.

Add JU8 on personality bd. to disable the live Data input. That ties it to gnd.

Open it if you want to enable Data input. It has a pull up resistor already on it.

Dual power mod. Cut trace at U2-13 on personality bd. Add 1K Ohm

pull-up resistor from J1-35 to U3-16 or plus side of C2. Add jumper from

pin 2 on the personality bd "Spare" con to the feed through nearest to the

letter "S" in the word "Spare."



On a frequency in the center of the ham band, check to ensure that the transmit and receive steering voltages are at the center of their control range.

Preselector and mixer filters

Loosen the lock nuts and tune preselector and VCO mixer adjustment screws (screw in.)

Optimize reception for a frequency in the center of the ham band. Retighten nuts.


Set R911 on common circ. bd for desired max power with power level sw Up.

Set R983 for desired low power with power level sw Down.

Set R517 mic audio deviation to under 5kHz deeviation at normal speech levels.

Note: Snug up the screws on the heat sunk transistors on the Com. Cir. Bd. if you haven't already. Apply heat sink compound between the heat sink of the hinged common cir. bd and the radio chassis.



Appendix B



The channel freqs are stored in the black plastic module (code plug) next to the 40 pin processor IC. It can be pulled out (it comes out pretty hard. Use both hands.) Once out, look it over carefully. It may be taken apart by sliding one side of the cover up and the other side down. This requires some muscle as well.

Once open, you will (hopefully) find a 2816 EEPROM socketed on the board. Carefully remove the EEPROM from the socket, noting the direction in which it is installed.

To do the frequency and parameter reprogramming you will need software to generate the data. There is some available on the web. One of the programs I've used is called SPROG. This isn't a plug for it, it's just one I recall that was free and there are others out there. You can decide which to use. What I can tell you for sure is that Motorola service shops are not guaranteed to support them any longer. And if they do, you won't want to pay the price.

When you have the data you want, you will need an EEPROM programming device that will handle these old 2816 EEPROM. Remember, these devices are parallel data devices, not serial devices. A serial device programmer will not work.

Once programmed, reinstall the EEPROM (in the proper direction) in its socket. Replace the two-piece plastic module cover and plug it back in. Then it's time to tune up your radio.



The following is something I wrote earlier and is a shameless plug for a cheap EEPROM programmer I'm working on. You'll like it. The prototype is already done and working and I'm finishing up the bd layout for production now. Check back with me on it.

Actually, I include this info because it has a lot to say that's helpful and of interest, and besides, I spent a lot of time writing it. :-)



Programming the code plug for the SyntorX


The SyntorX (there is no "XX," that's just a logo shadow effect, and not a very good one.) uses a 2816 EEPROM to store its frequency and other programmable info in. Each channel is called a "mode" because, unlike a typical ham radio, all the various parameters are predetermined for each "channel." For instance, where a typical "ham" radio can change such things as CTCSS tone, power level, and even quickly swap monitoring of input and output (on reverse) without changing the entered frequency, a SyntorX is stuck with whatever parameters were programmed into that "channel" mode.

There can be a lot of options for each mode, such as a variety of analog and digital CTCSS tones (even custom ones) Priority channels, power levels, and of course a wide band of frequency coverage. But the user is normally stuck with just 4, 8, 16, or 32 combinations of them because of the "mode" methodology used in the design of these radios. Let me give you an example of the problem for hams. Let's say I wanted to have a High and Low power option on each frequency I use. Since a mode is programmed with just a single power level I would have to use up sixteen of my modes to do high power and sixteen of them to do low power, without changing any other parameters. If I wanted to be able to work on "reverse" (swap input and output freqs) as well, then I'm already down to just eight actual channels with these various combinations of characteristics out of 32 modes programmed in. That ain't very versatile. And that's why a radio that can crank over 150 Watts typically sells for under a buck a Watt.

So what exactly is the upside to a 20 lb cast aluminum transceiver with limited versatility? Try the 150 to175 Watts or so of output, beautiful audio, and a rig you can hit with a water hose while backing over it with a truck, and still keep talking on it. Motorola keeps it reliable, potent and simple. And this simplicity is just exactly what is called for in real emergency communications applications. Several times I've heard hams over the air say that they'd like to go simplex with their fancy little Japanese 2-way rigs, but unfortunately they didn't know what buttons to push! And this is coming from guys with one by two callsigns! That's nuts. So there is a real place in the ham world for a powerful, reliable, no frills transceiver that anyone can use in a crisis without reading a 90 page owner's manual.

So far, the greatest difficulty I've found in the use of the SyntorX, and I own several of them for different bands, is getting access to an EEPROM programmer so I can reprogram the modes as needed. For instance, if my buddies decide to hang out on a simplex freq not already in my radio, I'm stuck.

So I finally broke down and bought the cheapest eprom programmer I could find. It was about $130, and it died after a couple of months. I wasn't happy, and I certainly wasn't about to buy another one for another $130. So my radio just sat there for a while. But the SyntorXs are the most potent VHF/UHF mobile radios around. They put out as much power as most $250 "brick" external amps do and they have audio like a voice from on high. Even the audio amp stage puts out 15 Watts! What's a rice burner radio push out of its speaker anyway, 2W? And I can get inside these large rigs and modify them to my heart's content without using a microscope. And I do. They even have a flip-up circuit bd that works like the hood of a car. Unlike the new micro radios, they beg to be played with. You can get at everything, and it's almost all standard stuff. From the first time I saw one I was hooked. But at that time I was still talking on a 32 Watt Japanese rice burner that sounded like I was inside a tin can. Sooooo... I said.....

"Enough!" and I designed this custom eprom programmer. Since it only has to program one single type of eprom I could make it simple and cheap. Also, since I already knew what type of info had to go where in the EEPROM I could custom design the software to accomodate it. For instance, if you decide you want to add a switch and bank select another 32 modes in the rig the prom programming requirements can get ugly in a hurry. While there are some good cheap or free programs out there to generate the frequency info, they only create 32 modes at a time, and if you create two 32 mode data files nothing will automatically place the second "bank" of 32 modes where it needs to be in the eeprom, except my programmer. And I'll give you a hint, that second bank of 32 modes doesn't go right next to the first 32 modes. Nope. This is Motorola! I had to learn to use a Hex editor in order to create my first 64 mode code plug EEPROM. That was ridiculous. I prefer to learn about things that are actually fun. So I've added a software function to this programmer to enable you to easily program in two separate 32 mode data files, and these "lower" and "upper" mode banks are automatically put in the correct places in the EEPROM.

Since building and using my first prototype of this programmer I keep one handy near the radio. They allow me quickly and easily change all my rigs channel "mode" attributes as needed. That makes a rig that's wonderful, but terribly awkward to program, much easier to use (and a whole lot cheaper to program) which makes the SyntorX very hard to beat. Especially by the little, low power Japanese rigs you can't figure out how to open up, or program to run simplex.

My programmer operates on a 9 Volt radio battery. I figure that's cheaper than a wall wart, provides ground isolation, allows for field reprogramming, and in general makes a whole lot of sense. Good, simple, cheap. I like that kind of thing.

Happy programming! -KB0ONB-




Remove the three retaining screws on the Common Circuits bd, (hinged bd.) On the RF bd below it you will find a black 7 pin jack (J250) beside 2 Xtals. The pin nearest the Xtal is pin one and the pins are numbered sequentially in a counterclockwise direction.

Connect a volt meter to pin 7 (gnd) and pin 2 (sig). This signal should produce readings somewhere between 2 and 5 volts DC. Remember to put the heatsink screw back in after connecting to the jack as tune up will take a little while.

On a freq near 146 MHz with the sig gen set to the lowest receiveable sig strength, adjust the preselector screw closest to the side of the radio for the highest reading on the meter in conjunction with searching for the lowest noise point. Then continue to work your way through the row of tuning screws until you get to the other end. Most, but possibly not all, will need to get screwed "in." But double check. Reduce the signal power from the generator enough to keep the signal noisy as you adjust. Repeat until satisfied. At -130 dBm I typically get a reading of about 3.08 volts. Note that the sig strength as read on the meter will jump around a bit.

Fortunately, the 2 meter band is only 4 MHz wide and the rig is very broadbanded, so it isn't necessary to do a spectrum analyzer sweep of the band to set the band edges as you adjust the preselectors, just tune for a peak DC voltage at 146 MHz. It works well for me.

With a 1kHz audio tone on the signal I still hear a reasonably good tone mixed with the noise at -130 dBm by the time I'm done. Carefully retighten the locknuts, then recheck the signal.

Click HERE for an interesting application for converted 2-meter Motorola SyntorX radios.