Galaxy DX45MP No AM TX - FM Works

[Chris Lawrence]

No AM TX but plenty of power on FM. Receive works. PA works. I accidentally discovered a small signal at 27.120 regardless of which channel it’s on when I looked up at my bench radio. Signal then checked on spectrum analyzer reading at coax-out and it shows up….low, but it’s there.

TP3 is on frequency on AM and FM (16.5100 on ch 20)

TP5 is on frequency on FM (10.6950 ch20) Can’t get freq counter to lock on AM.

It receives on the correct frequency, both AM and FM.

Q53,53,55 show good voltage.



Side note: The receive is poor and the RF gain does not attenuate the signal though the pot does function as it should.
Sinad=-12db@-84dbm

 

[nomadradio]

The 27.120 you heard is coming from the second harmonic of the PLL's 13.56 mhz crystal. Tends to clobber the radio's channel 13/14 receive. Can you hear even a weak carrier in another radio if you key it on the selected channel? A coax jumper on the monitor radio's antenna socket gets the shell backed off. The center pin becomes a sniffing antenna, to probe near the Galaxy's transmit circuits. If you do hear a carrier, this serves to narrow down where to look next. And if you don't, this points to the 10.695 carrier crystal's circuit. Only way I can think for that to happen would be for a switching diode to fail, like maybe D85?

Just a hunch.

73

 

[Chris Lawrence]

The 27.120 you heard is coming from the second harmonic of the PLL's 13.56 mhz crystal. Tends to clobber the radio's channel 13/14 receive. Can you hear even a weak carrier in another radio if you key it on the selected channel? A coax jumper on the monitor radio's antenna socket gets the shell backed off. The center pin becomes a sniffing antenna, to probe near the Galaxy's transmit circuits. If you do hear a carrier, this serves to narrow down where to look next. And if you don't, this points to the 10.695 carrier crystal's circuit. Only way I can think for that to happen would be for a switching diode to fail, like maybe D85?

Just a hunch.

73

I will take a closer look tomorrow but I really don’t think there is any carrier whatsoever on the selected frequency showing up on the “sniffing” radio. I will check D85.

 

[Chris Lawrence]

The 27.120 you heard is coming from the second harmonic of the PLL's 13.56 mhz crystal. Tends to clobber the radio's channel 13/14 receive. Can you hear even a weak carrier in another radio if you key it on the selected channel? A coax jumper on the monitor radio's antenna socket gets the shell backed off. The center pin becomes a sniffing antenna, to probe near the Galaxy's transmit circuits. If you do hear a carrier, this serves to narrow down where to look next. And if you don't, this points to the 10.695 carrier crystal's circuit. Only way I can think for that to happen would be for a switching diode to fail, like maybe D85?

Just a hunch.

73

D85 was toast. Replaced. Works well now. I’m a little baffled at the poor sinad reading though the receive is picking up as well as my Icom though the meter doesn’t like to budge unless there’s a big signal. I calibrated S9 at -67dbm. Two separate things though. Meter could be an issue. Not as important.

Thanks for the help.