Here's a fault we have seen in more than one newer Connex radio. This one is a CX46 with the amplifier under it. The problem occurs when the transmit audio gets "enhanced", or the modulation boosted in any way. The transmit audio will squeal no matter where the mike gain is turned. Turn it all the way down and it still squeals.
Bummer.
The clue here is that it squeals turned down. The problem is caused by using a single wire as the ground connection for both the RF Gain and the Mike Gain. They are on a double control. Sharing the same ground wire shouldn't be a big deal, right? In practice it creates a ground loop. The fix is to separate the counter clockwise (ground) lug of the rear mike gain section from the clockwise grounded lug of the front RF Gain section. Best way is to take the Dremel carbide burr to the foil on the Mike Gain's CCW lug. A new ground wire will connect the mike gain control directly to a ground foil in the mike amp, rather than to the ground wire on the radio's S-meter as the factory wired it.
Naturally you'll have to remove the knobs and face plate so you can loosen the control from the front panel. Can't get proper access to it any other way.
Yeah, I shoulda brushed away the crumbs after grinding it. Use a thin burr that won't sever the ground leading to the front RF Gain section.
A ground wire gets added to the lug we just separated from its foil pad.
There is an empty hole on the ground foil that runs alongside the mike amp chip. Oddly enough, it's marked "GN". Didn't get a pic of the solder side, but this should tell you enough.
This looks for all the world like a "something for nothing" sort of proposition. But this is not the only Connex model where we have found this quirk. Can't remember the other model number right now. The circuit-board number for this one is EPT3600-15C.
Or you could just leave the transmit audio turned down to the factory-stock level. Would be cheaper and easier.
A look inside some other models based on this type circuit board reveal two separate ground wires from the factory. Makes a difference.
73
Bummer.
The clue here is that it squeals turned down. The problem is caused by using a single wire as the ground connection for both the RF Gain and the Mike Gain. They are on a double control. Sharing the same ground wire shouldn't be a big deal, right? In practice it creates a ground loop. The fix is to separate the counter clockwise (ground) lug of the rear mike gain section from the clockwise grounded lug of the front RF Gain section. Best way is to take the Dremel carbide burr to the foil on the Mike Gain's CCW lug. A new ground wire will connect the mike gain control directly to a ground foil in the mike amp, rather than to the ground wire on the radio's S-meter as the factory wired it.
Naturally you'll have to remove the knobs and face plate so you can loosen the control from the front panel. Can't get proper access to it any other way.
Yeah, I shoulda brushed away the crumbs after grinding it. Use a thin burr that won't sever the ground leading to the front RF Gain section.
A ground wire gets added to the lug we just separated from its foil pad.
There is an empty hole on the ground foil that runs alongside the mike amp chip. Oddly enough, it's marked "GN". Didn't get a pic of the solder side, but this should tell you enough.
This looks for all the world like a "something for nothing" sort of proposition. But this is not the only Connex model where we have found this quirk. Can't remember the other model number right now. The circuit-board number for this one is EPT3600-15C.
Or you could just leave the transmit audio turned down to the factory-stock level. Would be cheaper and easier.
A look inside some other models based on this type circuit board reveal two separate ground wires from the factory. Makes a difference.
73
