MX3000 / Saber III - mic preamp or not?

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radio-link
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Joined: Sun Mar 16, 2003 8:49 am

MX3000 / Saber III - mic preamp or not?

Post by radio-link »

Hi out there,

I have here two Motorola MX3013, what is some kind of German police radio version of the Saber III / MX3000, VHF low, 75 MHz band. Now one out of 1991 performed just fine, while on the radio from 1994 TX audio was low and muffled. Alignment just fine, so I thought, maybe the mic. Replaced the mic, no change :( So I thought, maybe a broken C or R or something, hard to find without service manual, you have to live with it. The radio was usable and all, just had to talk a bit louder when TXing :-)

Two or three years later (just half an hour ago) I decided to have a closer look again, and I found that directly to the Mic connector on the main PCB some parts were missing on the 1994 radio. It was the circuit of a simple mic preamp, one transistor, two resistors, one capacitor, and the whole thing was missing and bridged with a 0 ohms R.

So I inserted a transistor, soldered the 10k and 4k7 Rs in place, also the 100nF cap - and that was it, identical mic sensitivity!

Now why did they change this? Is this generally known for those radios, or was it a special mod for German police, maybe for highly noisy environment?

Thank you for your ideas :-)
regards - Ralph, dk5ras

--

Ralph A. Schmid http://www.bclog.de ralph@schmid.xxx
Tel./SMS +49-171-3631223
momo737
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Joined: Tue Dec 22, 2009 9:31 am
What radios do you own?: MX3000 (SABER III for europe)

Re: MX3000 / Saber III - mic preamp or not?

Post by momo737 »

Hello,

I had the same problem with my MX3000, i have fixed it today by replacing the mic twice. When i replaced it with another one with the same size, it fails also (very weak modulation).

I started to think about looking for some circuits, but before, i have decided to check again and replaced the mic again with a bigger one, and it works now perfectly!

Take care about polarity, there is a 220 Ohms resistance between RTX ground and Mic ground (MIC unsoldered) in my model, no resistance in the other pin.

I didn't suspect the preamp because the radio works perfect with the external mike.

Check also the mic modulation level in the RSS: i have set it to +6 dB (choices are from -3 to +6 dB, 3db step).

Good luck :)

My model is MX3000, 136-174 Mhz, 12,5 Khz, 6 Watts
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radio-link
Posts: 245
Joined: Sun Mar 16, 2003 8:49 am

Re: MX3000 / Saber III - mic preamp or not?

Post by radio-link »

Hi,

mine were 68-8 8MHz / 6W with special firmware, and it had definetely nothing to do with the mic capsule itself, it really was this missing transistor. Strange.
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