Maxtrac Noisy Rx Perfect TX

Daniel Watson · Post by **Daniel Watson** » Thu Sep 16, 2004 9:33 pm

On RX this Maxtrac has a loud rushing noise in background. Modulation is noticable but there is more rushing noise than voice transmission. Checked connections, inter connect pins, grounds, speaker. TX & Rx on freq ok. Any ideas? Thank you

kcbooboo · Post by **kcbooboo** » Fri Sep 17, 2004 3:32 am

If you have the service manual and a good signal generator, you should be able to inject a signal into the front end and take some audio level measurements with modulation and without. Someone could have adjusted the quadrature detector coil, which would make recovered audio almost non-existant and leave you with a slight hissing sound. There's nothing that's mechanically tunable in these radios, and a former owner could have tweaked things; now you have it.

Does it do this with the microphone unplugged? I'm thinking that maybe an internal audio problem is picking up something from the mike.

That's the end of my guesses. Of course there could still be something actually broken, like a crystal filter. But by making some audio measurements with a modulated signal, you should get the voltages noted in the schematic.

Bob M.

Max-trac · Post by **Max-trac** » Fri Sep 17, 2004 8:00 pm

Is it by chance a 900MHz unit?
I did the conductive pen mods to the VCO on some 900 units and some of them had those symptoms. You could blow on it and change the rushing noise.

Daniel Watson · Post by **Daniel Watson** » Sat Sep 18, 2004 2:51 am

This is a UHF, 448-470 MHz BUT I never saw a Maxtrac where the Scan button said, EXIT instead of Scan? With Volume control almost fully open voice audio present but the noise is louder than the voice.

Post by **xmo** » Sat Sep 18, 2004 6:35 am

Six channel Maxtrac 300 models did not come with scan. On those models the middle button was labeled "Exit"

Daniel Watson · Post by **Daniel Watson** » Sat Sep 18, 2004 4:07 pm

Hmmmm something strange. This radio has 16 freqs and scans when I push that exit button? Maybe this one has the wrong control head on and this is causing me problems?????

Post by **xmo** » Sat Sep 18, 2004 5:22 pm

The 6 & 16 channel front panels are the same except for the plastic escutcheon. If you post the radios's model number from it's tag and the model number that the RSS says the radio is - that would be a starting point to determine what you have. To be sure - you should also find the part number of the radio's logic board and the radio's firmware chip.

Your radio may have been 'field upgraded' or it may just have had its front replaced. Either way - your problem sounds like an RF board issue.

Daniel Watson · Post by **Daniel Watson** » Thu Sep 23, 2004 4:21 am

Here are some numbers
Chassis HUE3052C
RF board HLE9310B (449-470 MHz)
Logic Board HLN9313A (full options & Expanded board)
Model # D44MJA7DA5K (read, no tag)
Maxtrac 300 16 channel (read)
This radio is suppose to be a Maxtrac 300 16 channel 40 Watts with a band split of 449-470 MHz.
Does anyone know if these numbers match?

jackhackett · Post by **jackhackett** » Thu Sep 23, 2004 5:15 am

If you have an oscilloscope you can look at pin 3 of the rf to logic board connector, with a strong modulated signal you should see clean demodulated audio at this point, if you do, the problem is in the audio circuit on the logic board, if it's very noisy the problem is in the rf board. That would at least narrow it down a little.