M120 Strange Sticker on heatsink - Please Help

aussie_battler · Post by **aussie_battler** » Fri Jun 16, 2006 4:30 am

Hi everyone

I have just aquired a M120 M44GMC20A4AA in good condition out of a work environment.

I don't think the radio has been modded as it came from a landscape supply place and it doesn't appear to be touched in any way inside the radio just by looking at it.

I have taken it to get programmed to 40w and paid the guy, took it home, set it up and it is doing only around 25w.

So I took it back to the guy and he kept it overnight (he doesnt speak the best english either) and I went back and got it the next day (no charge) and he said that the output transistor won't go to 40w and it cant be done.

I don't see how or why when the model number corresponds to a 40w radio.

ALTHOUGH, and this is where my question comes in, there is a sticker on the back that says this:

'SMA Approved M120 25w / 25 KHZ'
'FREQ (MHZ) TYPE NO: APPRO NO:
'403-420 GMCE-25 235WB305'
'450-470 GMCF-25 235WB0022'
'470-500 GMCG-25 235NB0055'
'500-520 GMCH-25 235NB0052'

That sticker is next to the normal motorola model and serial number sticker, underneath the heatsink.

What does that sticker mean? Why is it there? Do I have a dud radio?

Any suggestions?

I hope someone can help me.

Thank you very much for reading all this.

(PS. How many amps should it draw at 45w?)

Al · Post by Al » Fri Jun 16, 2006 5:16 am

It almost looks like the 'special' sticker that you mentioned is something required by your federal government for type approval under Australian law. According to the Motorola model number sticker, your unit should be capable of 40W. If you remove the heatsink from the rear of the radio(2 torx screws) after taking the skins off top and bottom, you should see a PA model number on the PA shield facing the front of the radio. If you can check this number(probably an HLExxxx), you can verify the design capability of the PA. While you have the PA removed, remove the shield mentioned above and check for melted/overheated solder joints around the collector tabs of the flange-mounted output transistor on the PA PC board. It's very common for these joints to overheat, opening up the matching capacitor-to-ground connections, and then the radio won't make rated power. With 35-40W output, the radio should draw 12-14 A from the 13.8V supply.

aussie_battler · Post by **aussie_battler** » Sat Jun 17, 2006 4:06 am

Thank you Al

The radio is currently only drawing around 8 amps.

I'm not a technician of any sort but I will be buying a small set of dick smith torx screwdrivers and I will do as you said and check the number.

What is the number that I should be looking for?

I will be ordering a programming lead I think and that way I can program it myself.

As I don't have a SWR metre, can someone tell me what number in the software to set it to for 45 watts (50 if its possible)?

I have heard it goes from 0-120 (the number in the software that is).

Thank you again

aussie_battler · Post by **aussie_battler** » Sat Jun 17, 2006 4:08 am

I did a little more research and found that SMA is what the ACMA (Australian Communications & Media Authority) used to be called.

I hope that the presence of that sticker doesn't mean it has been limited in some way by them.

Anyone else ever heard of this being done on an M120 or any radio for that matter?

kb0nly · Post by **kb0nly** » Sat Jun 17, 2006 12:04 pm

It's very possible that they limited it to 25W to stay within some regulation for the service it was intended. I'm not familiar with the regulations over there however.

If your going to be messing with the PA settings you better beg or borrow a wattmeter off someone to keep tabs on it while setting it. And DO NOT go over the rated power of 40W if that PA ends up being capable of it. I have seen VHF units, which have a high power rating of 45w, set to 50w and run that way. Sure, they will do it, but unless you liquid cool the PA heatsink with liquid nitrogen expect the radio to die a short painful death. They get SUPER hot! I had one on the bench here one time that someone set to roughly 50W, it was making about 48-49 on my Bird 43 after i hooked it up to check why the radio was so blooming hot and tried to take it out on my fingers when i accidently touched the heatsink after smelling something weird. It was cooking the dust off the heatsink fins, and i swear i could put a quarter pounder on there and have dinner.

Also remember that the Maxtrac/GM radios were intended for commercial use where the transmissions are short and sweet and to the point. A higher transmit cycle, longer transmissions, and that puppy will get hot fast. They just weren't built for it. I have taken the 40w UHF Maxtrac and made them into repeaters, but you have to run them around 20W and force air cool the heck out of them to keep from burning up the PA. Which is what Al was talking about in his post, too many long winded conversations and the final gets hot enough to melt the solder joints. i have seen VHF Maxtracs with molten solder dripped down onto the metal shiled inside them from getting too hot.

I have been experimenting with the idea of taking a Maxtrac PA and machining off the rear fins and then attaching a larger heatsink with cooling fans to pull the heat away from it better. Than perhaps a guy might be able to run full power with a higher duty cycle and make them more reliable in repeater use.

Will · Post by **Will** » Sat Jun 17, 2006 11:50 pm

kb0nly wrote in part "I have been experimenting with the idea of taking a Maxtrac PA and machining off the rear fins and then attaching a larger heatsink with cooling fans to pull the heat away "

The big problem on the Radius/Maxtrac mobile heatsink is that little 'bump' the final PA transistor sits on. The 'bump' or pad is not a good heat conductor.

I am thinking a new much larger heatsink with the PA transistor bolted directly to it.
Or the R1225 Hi power repeater heatsink that has longer fins.

aussie_battler · Post by **aussie_battler** » Sat Jun 17, 2006 11:56 pm

Okay thank you for that advice.

I will not be transmitting for too long in it at all. The only time I will be using it is for short periods when I can't get through on my local repeater due to people driving near the repeater and buttoning (Yes CB).

I have two fans here that I will be putting on and running whenever the radio is on to help keep it cool.
Plus my antenna is brand new and I run LDF-450 feedline.

I'm not sure if I'll be able to gain access to a SWR metre, so if possible could someone tell me which number to set it to in the software (0-120) to get 40 watts? (It would be the same for all M120's I guess?)

Thank you

<Insert signature here>

DES-AJ · Post by **DES-AJ** » Sun Jun 18, 2006 7:45 am

That would be incorrect.

Alignment and/or tuning isn't as simple as "A number from 0-120" theirs a lot of factors that go into it.

Each (or at least most) of the tuning settings can impact the 'value' you set to gain the power output you desire. Every radio is different so even if you had a friend with the same model radio and they had tuned theirs to "40W" if you set the same values in your radio you might not get the same outcome.

aussie_battler · Post by **aussie_battler** » Sun Jun 18, 2006 8:48 am

Okay thank you for that.

I will have to get a SWR metre from somewhere then.

Anyone ever had any luck at running an M120 at 50 watts?

Thanks

kb0nly · Post by **kb0nly** » Sun Jun 18, 2006 9:14 am

Again, if you want 50W your better of either getting a different radio or an amp that you can flip on when you need the extra oompf.

You could just leave the radio at 25w and get an amp off ebay for less than $100 and accomplish the same thing, the added benefit is the amp is taking the heat and most of them out there have far better heatsinking than the radio you have.

aussie_battler · Post by **aussie_battler** » Sun Jun 18, 2006 9:57 pm

Thank you, yes I am aware of all this. I will not be using it for long periods of time.

Has anyone ever run one of these at 50w though?

Thanks you

kb0nly · Post by **kb0nly** » Sun Jun 18, 2006 10:32 pm

I already mentioned that yes it's possible, and yes it has been done, i personally had a UHF high power unit that would do about 53W, but after 3-4 short transmits of less than a minute each you would already start smelling hot heatsink.

Bottom line, again, don't run it that high regardless of how short the transmit time is, you will just end up destroying the PA.

aussie_battler · Post by **aussie_battler** » Mon Jun 19, 2006 12:05 am

Thank you kb0nly for your answer

The reason for asking is I want to set it to 50w for that extra 1dB gain up from 40w.

I will heed your advice and not be keying up for more than 30 seconds at a time and makign sure it has a rest in between.

I'm also going to put fans on the heatsink to cover the whole thing.

Thank you again for your help.

If anyone else out there that reads this post knows what the SMA approved sticker means:

'SMA Approved M120 25w / 25 KHZ'
'FREQ (MHZ) TYPE NO: APPRO NO:
'403-420 GMCE-25 235WB305'
'450-470 GMCF-25 235WB0022'
'470-500 GMCG-25 235NB0055'
'500-520 GMCH-25 235NB0052'

please let me know as I check the forums daily. I have found that the SMA is what the ACMA used to be called.

Does anyone know if the radio just had that sticker put on it so techs wouldnt program it past 25w or is it there because the SMA actually removed the 40w finals from it and replaced with 25w? Is that likely to happen?

I have two radios with the same sticker from the same place. Both are meant to be 40w radios according to the model number on the back of them, except for this damn sticker.

Thank you agian to everyone who has replied so far and I hope someone can solve this mystery.

If no one else can solve it, I will be solving it myself soon when I order a programming lead. But that will take around 2 weeks to arrive.

Thanks again.

Bruce1807 · Post by **Bruce1807** » Mon Jun 19, 2006 2:20 am

'SMA Approved M120 25w / 25 KHZ'
'FREQ (MHZ) TYPE NO: APPRO NO:
'403-420 GMCE-25 235WB305'
'450-470 GMCF-25 235WB0022'
'470-500 GMCG-25 235NB0055'
'500-520 GMCH-25 235NB0052'

The M120 had 4 different RF boards for the above bands.
Looking at the sticker contents
403-420 (This used to be government only when I lived in Melb)
and 450-470 are approved for Wide Band (25khz)
and the other 2 are approved for Narrow Band (12.5khz)

All the sticker is saying is the radio is only approved for 25 watts. If you crank it up you are breaching the approval process. It doesn't mean its been modded in any way to meet those approvals. We used to be able to crank our Syntors up to 50W although they were only approved for 25Watts

So if we take the first line
'403-420 GMCE-25 235WB305'

GMC (M120 model)
E is the band 403 -420
235 is probably the type acceptance catagory for a M120
WB wide Band
305 will be the rest of the approval for that specific model

50 watts out of a M120
You trying to make an electric barbie! (slang for bar-b-que for our NA friends)

aussie_battler · Post by **aussie_battler** » Mon Jun 19, 2006 6:52 am

Thank you so much Bruce.

It makes sense now.

now all I have to do is wait for my programming cable to arrive!

Thank you for putting me out of my misery.

I can't believe I didn't see it!

Thanks again and thank you to everyone else in this thread who added their two cents

regards, aussie_battler

aussie_battler · Post by **aussie_battler** » Mon Jun 19, 2006 9:48 pm

Now to get my money back from that wanker who couldn't perform a simple task for fee.