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Maratrac no audio

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Maratrac no audio

Postby 911-EMT » Thu Jun 18, 2009 9:05 am

Hi I am working with a maratrac mobile I programmed it but could not get audio out of it the busy led gets on when it receives signals but no audio from the speaker any idea

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Re: Maratrac no audio

Postby maxkelley_kc2spy » Thu Jun 18, 2009 11:59 am

Not sure why there's multiple postings of this, but anyhow, if you have the A9 advanced control head, press the Mon button so the red light lights up. That disables the PL squelch. If you still hear nothing, press and hold the Mon button, you should eventually hear static from the speaker, check volume control of course if you don't.

If none of that works, you've got something more serious inside the radio.
Max Kelley KC2SPY
MT2000 VHF & UHF A7, Visar UHF, ASII UHF, Maratrac UHF, Astro Spectra UHF, MCS2KIII 900, XTS2.5K-Q

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Re: Maratrac no audio

Postby Pj » Thu Jun 18, 2009 12:49 pm

PLEASE click once! Other topics removed...
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Re: Maratrac no audio

Postby 911-EMT » Thu Jun 18, 2009 3:59 pm

i tried mon but didn’t helped and the busy led get on so i know the radio receives signals, i have tried taking audio from vip but no luck, any mute option i missed anyone can think of with start alert

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Re: Maratrac no audio

Postby kc7gr » Sun Jun 21, 2009 7:10 pm

The Maratrac is basically a Maxtrac with a big power amp attached. This means it has (ultimately) the same guts in the receive audio section as the Maxtrac. This means it is a 'balanced' output circuit. Shorting either speaker lead to ground will cause the output chip to blow itself up.

This may very well be what's happened to your radio. The only way to tell is to get it on the bench, feed a signal into it, and start tracing the audio between stages with an oscilloscope.

If this sounds scary, or if you lack the necessary test gear, I can repair the radio for you at my normal rates. Please feel free to drop me a PM if interested.

Happy tweaking.
Bruce Lane, KC7GR
"Raf tras spintern. Raf tras spoit."

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Re: Maratrac no audio

Postby chartofmaryland » Mon Jun 22, 2009 5:03 am

Open the radio and look at the blue capacitor near the antenna relay. If there is a amber looking goo near them the audio goo has dried out and left the radio taking your audio with it.

If you have testing skills check the audio path with an oscilloscope. Make sure to not ground your probe tip against ground when testing or you will make more things want to leave.

If the lights are out when you leave the station and then come on the second you key up, you know you have enough power.

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Re: Maratrac no audio

Postby kf4sqb » Mon Jun 22, 2009 1:32 pm

Which control head do you have on it, clamshell or A7? If it's the A7, it uses an electronic step-attenuator inside the head to control the volume. This step-attenuator uses a separate +9VDC regulator circuit for it's power supply. As best as I can remember, this 9V regulator supplies the volume control circuit only, and you will get absolutely no audio output if it isn't working. There is also a possibility that the shift register that the volume rocker drives has gone bad. If you need it, I can send you the schematics and board layouts of the A7 control head, as well as give you some troubleshooting tips for the problems I've described. I've already been through this issue myself a few years ago.
kf4sqb "at" wetsnet "dot" com

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