Maxtrac Wont transmit on a frequency

[centuryvrproductions]

I Just got a 40W Maxtrac 300 for my repeater

It just wont transmit to my Repeaters frequency of 444.500MHz. It transmits for a sec and stops.

It seems to transmit fine on 449.500. (Duhh, its in the bandsplit range)

The bandsplit is 449-470 or somthing like that, and I want it to transmit out of that to 444.5

I have 25W radios running with the same bandsplit and they work great on 444.500

Is there a way to fix it to work? I guess the 40W radios are different in tollerating out of band frequencys?

anyone have any Ideas?

 

[mmckenna]

Is there a way to fix it to work? I guess the 40W radios are different in tollerating out of band frequencys?

anyone have any Ideas?

Bending them out of band will likely have different results for different radios. It sounds like an alignment on the radio would help things. Likely it's just on the edge of working. When you key it up, the voltage drops a bit, likely just enough to drop the VCO out of lock.

Just a guess though. I'd have it aligned. You could also make sure that it's not being starved for power when it keys up.

 

[jim202]

Bending them out of band will likely have different results for different radios. It sounds like an alignment on the radio would help things. Likely it's just on the edge of working. When you key it up, the voltage drops a bit, likely just enough to drop the VCO out of lock.

Just a guess though. I'd have it aligned. You could also make sure that it's not being starved for power when it keys up.

Don't tell the man to have it aligned when he is trying to operate the radio way outside the designed band split.

All the mods I have done have been on a Spectra. There are a couple of good papers on how to move the radio down into the range you need. Most of them require that you get into the CVO circuit board and make a change to the ceramic substrate plated circuit. The best place to start is to measure the VCO voltage test point. You will need to pull off the cover to get at the RF board in the radio. You will then measure pin 3 on the VCO board.

I would suggest that you add several channels to the radio so you can walk it down to the frequency you need. Like every 0.5 MHz from where it works to the point you need to go. Make up a chart and plot the VCO voltage that you measure.

There are 2 ways to modify the circuit trace. One is to use a conductive material and the other is a small soldering iron with low melt temp solder. I use a magnifier scope we have at work for looking at circuit boards to look at the VCO trace. It has been cut with a laser, so there are burn marks at each slice. I use some alcohol to clean up the mess and see where the slices are. You will probably need to add about 3/16 of an inch onto the main trace that is being used.

The voltage you need is about 3 to 5 volts on the VCO test point. I know it is hard to take off the VCO board.

Before I go too much further, I should probably go find one of the UHF Maxtrac radios I have and make sure they are of the same style VCO circuitry.

 

[centuryvrproductions]

sounds about right

yea, It worked for a while on 444.5 in that time it worked, when it keyed up. i would hear a wierd buz and then the buz would slowly fade away as my audio would slowly come in.


almost as if it was warming up and took a minute for the audio to fade in.

then after a while it started to key up for a sec and stop

 

[cmdrwill]

yea, It worked for a while on 444.5 in that time it worked, when it keyed up. i would hear a wierd buz and then the buz would slowly fade away as my audio would slowly come in almost as if it was warming up and took a minute for the audio to fade in.
then after a while it started to key up for a sec and stop

The TX VCO (in your Maxtrac) is operating WAY out of range and going out of 'lock'. You may be able to adjust the VCO coil to bring it into the normal lock range.

The real problem is the calibration settings for the transmitter are not supported by the firmware at any freq below 449.. So the freq, modulation and power control are not working at the 444.5 channel. So the transmitter will run at full power and the deviation, modulation, may not be correct at 444.5.

 

[mancow]

I would say it's a bad radio. I have Maxtracs and GM300s that work just fine down to 440. I've never seen one that doesn't. I have two setup right now as a repeater 444.100 / 449.100.

 

[centuryvrproductions]

Yes, I have two 25W maxtracs and they work great as a repeater 444.5/449.5. no problems

It does sound like a bad radio. I have had this issue (audio fading and buzzing) on other frequencys also, less of a problem as it would "warm up" or bring in the audio quicker

If so, Is it posible to swap parts from a 25W Maxtrac? Or remove the PA and put it on my repeater transmitter for the 40W power


Does it sound like the Power amp, or the RF board is Bad?

 

[mancow]

Hard to say. It could be a bad cap somewhere or bad solder joint, any number of options possible.

 

[centuryvrproductions]

Also It seems to be putting out only 25-30 watts. I ran it through a watt meter and got 25W. Thats probably off a bit because i ran a long lenth of RG-142 to the meter so there was loss, but still. That much?

and it gets Really hot to the point where i just couldnt toutch it after a few mins of talking here and there

 

[centuryvrproductions]

Ok. on all frequencys it transmits ok at times but mostly Distorted audio fading in and out...

I Tuned it down to 35W, no change...
changed deviation no change... As expected

 

[kayn1n32008]

Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)

Also It seems to be putting out only 25-30 watts. I ran it through a watt meter and got 25W. Thats probably off a bit because i ran a long lenth of RG-142 to the meter so there was loss, but still. That much?

and it gets Really hot to the point where i just couldnt toutch it after a few mins of talking here and there

Not suprising, you are trying to go along ways from the radios spec. I have a 25w 146-174MHz M120, that at 146MHz will put out 25w, but going *LESS* than 2Mhz (1.61MHz actually) lower, results in only about 14w with the same draw. Save yourself some time and trouble and find a Maxtrac, M120, or GM300 that is the correct band split.

 

[centuryvrproductions]

yes but this one as a real problem. If it doesnt work on that low a frequency then i will just use it to reach the repeater not transmit from the repeater.

It has the problem on the entire bandsplit.

 

[kb0nly]

Moving a 449-470 MHz MaxTrac to cover the 440-450 MHz Amateur band All the info you need to know.

As for the other problems in this radio it sounds like a bad interconnect. The RF board and logic board connect together through a multi pin connector that goes through the middle of the chassis, they sometimes get intermittent, removing the logic board and spraying the contacts with contact cleaner and reseating it a few times usually cures it.

 

[kb0nly]

Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)



Not suprising, you are trying to go along ways from the radios spec. I have a 25w 146-174MHz M120, that at 146MHz will put out 25w, but going *LESS* than 2Mhz (1.61MHz actually) lower, results in only about 14w with the same draw. Save yourself some time and trouble and find a Maxtrac, M120, or GM300 that is the correct band split.

You can't find one of "the correct bandsplit" as all the UHF models are 449-470. Yes there was some 403-430 models as well, but none that natively covered the ham band.

I use a bunch of them on UHF and VHF, a little tuning goes a long way. You can take a 150-174 split Maxtrac and reinit it as a 136-150 radio, do a full transmit alignment and adjust the VCO's and they work great with full power output, i have done dozens.

 

[kb0nly]

Also It seems to be putting out only 25-30 watts. I ran it through a watt meter and got 25W. Thats probably off a bit because i ran a long lenth of RG-142 to the meter so there was loss, but still. That much?

and it gets Really hot to the point where i just couldnt toutch it after a few mins of talking here and there

They all get hot... You have to remember these were made for a very low transmit duty cycle when used in the commercial service, they were not made for our rag chewing. A fan goes a long way.