Hello,
I have a UHF GP340 (comparable to the HT750) that seems to fully function, except it has no audio from the internal speaker at all.
I believe this was caused by pins on the accessory connector momentarily being grounded that should not have been. It was suggested from Motorola that the problem is likely with the Audio Amp IC or possibly a capacitor that opened up. They also said it may be possible that the unit has lost it's ability to properly sense when an accessory is attached, and the internal speaker may be muted thinking there is still something plugged in.
In testing I wired a pair of earphones to pins 1 and 2 of the accessory connector and I am able to hear all sounds in the earphones. I also opened the unit and applied sound from a PC sound card to the solder joints of the internal speaker and the speaker successfully plays the injected sound while the unit is off, which tells me the speaker is not bad.
Since audio is still being sent to the accessory connector, and since the internal speaker itself is not bad I got the idea to combine the two. When I connect the audio pins of the accessory connector to the internal speaker while the unit is on it successfully plays all audio as designed. To do this permanently I run two wires from the speaker inside the unit, through a small opening in the front cover wall to the outside wall, and under the escutcheon label to the accessory connector. The wires are kept where I need them by the pressure applied by the accessory dustcover.
This method works fine for me, since I am now able to use the unit normally without purchasing an external speaker/microphone. I mentioned this to Motorola and they said that if the accessory connector is not designed to use that type of speaker it could put stress on the audio circuitry, and I could loose that audio also. They said that the impedance and signal of the audio output needs to support or match the type of speaker used. I am currently operating the large internal speaker with the intended impedance of the smaller external accessory speakers.
I do notice that when I turn the volume more than 1/3 of the way up the audio seems louder than it originally did, and it starts to distort the higher you put it. This is fine the way it is for me functionally, because I don't need to turn it very loud, but I also want to preserve the radio and not loose the audio I still have.
My first priority is to make sure the audio circuitry is not stressed by what I am doing, and my second priority is to see if I can get the audio and volume levels to function as they originally did using this method, which is less important to me.
What I wanted to know was if there was a way to match the impedance or signal output from the accessory connector to that of the unit's internal speaker using components such as resistors to make it safe? The speaker being used is the original internal speaker, and it is part number 5085962A02. I am not familiar with the impedance value or ratings of either the internal speaker or the intended external accessory speaker, so I am looking for someone who is.
Thank you very much, any help is appreciated.
GP340 with no audio / Matching speaker impedance
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Matching speaker impedance
Thank you for your reply.
I unfortunately do not have another unit handy to test it with. I do believe the problem is with the mainboard and not the flex connector, however that is a possibility. This problem with the loss of internal audio occurred only after I inadvertently applied negative voltage to the incorrect pins on the side connector, instead of pin 7 which is the correct ground pin. When I did this I heard a loud "grinding" noise being emitted from the speaker, and the unit has never produced audio internally since that moment.
I am satisfied with what I have done because I have essentially restored the missing audio to the internal speaker by tapping into the side connector. I have the unit looking and working like nothing is wrong with it, without the need of a speaker mic. I would also prefer the unit without the speaker mic, because it is less bulky.
I was told by Motorola what I am doing is fine, but that I need to make sure I match the impedance of the speaker. The side connector is designed for a smaller speaker as used in the speaker mic's. I am now instead using the units "larger" internal speaker, which the side connector is not really designed for. It works perfectly fine for me right now, but Motorola said after long term use there is a possibility this could stress the audio circuits, and I could loose this audio also.
What I wanted to know was if there was any resistor or other component that I could insert in series into this circuit I am using to make it a safe load, or if that is even necessary if I don't turn the volume very loud? My goal is to find the impedance value or other ratings of a safe load for the side connecter (like a speaker mic), find out the same for the internal speaker, and match them with simple components.
As always, any help is appreciated.
I unfortunately do not have another unit handy to test it with. I do believe the problem is with the mainboard and not the flex connector, however that is a possibility. This problem with the loss of internal audio occurred only after I inadvertently applied negative voltage to the incorrect pins on the side connector, instead of pin 7 which is the correct ground pin. When I did this I heard a loud "grinding" noise being emitted from the speaker, and the unit has never produced audio internally since that moment.
I am satisfied with what I have done because I have essentially restored the missing audio to the internal speaker by tapping into the side connector. I have the unit looking and working like nothing is wrong with it, without the need of a speaker mic. I would also prefer the unit without the speaker mic, because it is less bulky.
I was told by Motorola what I am doing is fine, but that I need to make sure I match the impedance of the speaker. The side connector is designed for a smaller speaker as used in the speaker mic's. I am now instead using the units "larger" internal speaker, which the side connector is not really designed for. It works perfectly fine for me right now, but Motorola said after long term use there is a possibility this could stress the audio circuits, and I could loose this audio also.
What I wanted to know was if there was any resistor or other component that I could insert in series into this circuit I am using to make it a safe load, or if that is even necessary if I don't turn the volume very loud? My goal is to find the impedance value or other ratings of a safe load for the side connecter (like a speaker mic), find out the same for the internal speaker, and match them with simple components.
As always, any help is appreciated.