Uniden grant xl echo board removal

[MKwrench]

If the outer ring of the jack is grounded, the speaker will always be working.

 

[red97k1500]

I haven’t made much progress, I haven’t messed with this radio much in the last few days. But I can confirm that disconnecting the wire going to pin 3 of the mic socket made no difference. Even with mic unplugged I’m still getting receive from both internal and external speaker at the same time. I’ve been comparing this radio to an an unmodified 1989 148 gtl that works. On both radios the outer ring or barrel of the ext speaker jack is ungrounded, until you plug a mic in, then it becomes grounded, if I key the mic the line goes open.

 

[brandon7861]

If the outer ring of the jack is grounded, the speaker will always be working.

Then that means any of the chassis ground to board ground caps are suspect. Maybe someone replaced one with a bridge wire.

 

[red97k1500]

I’m just going to replace c240, that’s one that I never checked I might just replace all these little ceramic disc caps that go in between the ext speaker and pa jacks. Most of the are blackened and charred looking on the outside. C240 c169 c166 etc. at first I thought someone had jumpered one of these disc caps, but then I was able to see its labled jv13 and I’m pretty sure it’s factory. I’m still trying to compare this radio to two unmodified pc412 cobra 148 gtls. Basically I’m conducting the tests you mentioned earlier on the 148s to try and figure out how a fully functioning one should behave. I also have traced all the wires connected to the mic socket and am 99% sure they are connected how they should be in there factory locations. I still have a hunch that I am dealing with a failed component. I’ve even thought about swapping out the ext speaker jack with one from a parts radio, but I don’t think that will accomplish anything. I think it’s time to do some parts swapping, on some of these caps.

 

[brandon7861]

If the chassis is shorted to board ground somewhere, I would be tempted to put a 500mA constant current source across the leads of a voltmeter (connected at the probe tips) and measure the voltage across each of the board-to-chassis caps.

The closer you get to the short, the lower the mV reading will be. Just be careful not to inject that much current into something that cannot handle it (in this case, stay between board ground and the chassis). You should use auto-range on the meter too because there will be a higher voltage across the probes until you probe something.

edit: its basically an ohm meter with a little more oomph so we get a measurable voltage drop across a low resistance. And obviously, this would be done with the mic disconnected.