Transceiver: Sound and mic not working

There is no sound from the speaker when in RX mode. The RX circuit seems to be working fine as you can see it picks up the signal and shows RX on the screen.

The mic(sound input) is not working as well as I tested it by pressing the PTT, speak to the mic and listened from the other transceiver, the signal goes out but there is no voice at the other transceiver.

I already tried turning the volume to the maximum but still no sound.

Seems to be an analog circuit problem but I am not sure which parts I should check and replace. I checked the circuit board and did not see any parts broken.

Please advise. Thanks.

Here is the diagram.


Note: The turn-on beep sound works, the setting beep sound works, the call sound come out from the transceiver speaker but it is not transmitted into the air(the transmitting circuit works but no sound come with it).

If you are hearing even a little tic sound, the amplifier should be ok. One thing on video that battery seems to be empty, could that be little low battery? Another suggestion from the schematic is that there is an input for external mic at the bottom left corner and the signal goes through that jack, in another word if you decide to use external microphone then the internal would be cutoff completely check that circuit. While speaking in to the microphone check ic 5 section "c"
of lm324 op-amp with an oscilloscope to see any amplification is there, at r-113. Then check TP-9. Many things are not readable as the jpeg is not very high resolution. q17 supposed to mute the whole amplificaton of the microphone so check to see no voltage is present at the base. Check pin 12 of tb31202fn which is switch and is responsible for muting the microphone. Then post your finding.

yo2550 said:

There is no sound from the speaker when in RX mode. The RX circuit seems to be working fine as you can see it picks up the signal and shows RX on the screen.

The mic(sound input) is not working as well as I tested it by pressing the PTT, speak to the mic and listened from the other transceiver, the signal goes out but there is no voice at the other transceiver.

I already tried turning the volume to the maximum but still no sound.

Seems to be an analog circuit problem but I am not sure which parts I should check and replace. I checked the circuit board and did not see any parts broken.

Please advise. Thanks.

Here is the diagram.
View attachment 90593

Note: The turn-on beep sound works, the setting beep sound works, the call sound come out from the transceiver speaker but it is not transmitted into the air(the transmitting circuit works but no sound come with it).

Click to expand...

Note: The turn-on beep sound works, the setting beep sound works, the call sound come out from the transceiver speaker but it is not transmitted into the air(the transmitting circuit works but no sound come with it).

Click to expand...

So Amplifier working fine as u can hear beep sound.

As Mr. burt007 said chk the battery. Because…
If the battery is weak the voltage will get reduce when it consume more power during Tx and Amplifier with loud sound. Until that during normal condition voltage of the battery will seems good.

I already tried to listen by a headset and got the same result. Notice a short static sound when RX appeared on screen but no voice, same as when without headset. Seems that the mic and headphone jack works ok. I don't have an oscilloscope. I will try to check those parts and post a result later. Any more ideas are welcome.

Here's the pdf format of the diagram. Hope this helps.
http://www.tempfiles.net/download/201305/300864/TH7_X7A.html
http://www.tempfiles.net/download/201305/300883/TH7_Technical_Description.html

Check the plug/jacks where the accessories plug in they must re- make when accessory is removed , I am not shure why this would affect bot Tx and Rx audio,,? but I don't know that radio, and I only work on them now as my hobby.

If I replace the two ICs, do you think the problem will be fixed? Any other parts should I replace? I charged the battery to full and the problem still exists. The problem is in audio(voice) in and out function, might be the tb31202 that you mentioned. There are two lm324 and one tb31202fn that i'm going to buy. So any other parts should I buy with those ICs?

yo2550 said:

I already tried to listen by a headset and got the same result. Notice a short static sound when RX appeared on screen but no voice, same as when without headset. Seems that the mic and headphone jack works ok. I don't have an oscilloscope. I will try to check those parts and post a result later. Any more ideas are welcome.

Here's the pdf format of the diagram. Hope this helps.
http://www.tempfiles.net/download/201305/300864/TH7_X7A.html
http://www.tempfiles.net/download/201305/300883/TH7_Technical_Description.html

Click to expand...

I recently got a little scope[ a kit sort of?] a DSO on Ebay for 31 us$,, it will only go 4 megs , but I wanted to take it apart to see how it's made.And how they are programmed . Thats the cheapest scope, thye got better better ones ready made This cheapie is good good enuff for audio and dig wave forms and has storeage

kb5zxm said:

I recently got a little scope[ a kit sort of?] a DSO on Ebay for 31 us$,, it will only go 4 megs , but I wanted to take it apart to see how it's made.And how they are programmed . Thats the cheapest scope, thye got better better ones ready made This cheapie is good good enuff for audio and dig wave forms and has storeage

Click to expand...

Thanks for that. I will have a look at it. But this time I want to save my time by replacing a new ones. So I'd like anyone's recommendation all the parts I should replace to probably fix the audio in/out problem.

Just tried replacing Q23 from another working one but nothing's changed. The squelch is working. Try to turn on the squelch but still cannot hear static sound from the radio.
Any more suggestions?