Make DIY electronics - Alfred73

Jingtong annoying tone mod

Here is the faboulous jt-208 transceiver (136-174 mhz) and it's mod to cancel or reduce that annoying tone coming up at startup. First of all, this beep removing operation is a little bit delicated so is required a good practice with smt component soldering/desoldering. Do not attempt to do it if you have never opened any electronic device. About the opening of the case you can refer to this link. Once you have removed the cover, you have to desolder the 2 ground link that solder togheter the 2 board of the transceiver. Then, look at the other side of the keyboard , you will see near the mic and the speaker hole, a little smt transistor, which is used to amplify the beep signal coming from the pin 12 of the micro. Between that transistor and the mic there are an smt capacitor and a resistor . That capacitor bring the beep signal coming from cpu to the audio stage.To reduce the tone volume you have to substitute that capacitor with one of 5Kpf better if smt package. Be carefull in desoldering and soldering, use the minimal necessary temperature to not broken the link. If you completely remove the capacitor you will never ear any beep even from keyboard pressing. After that, carefully reinsert the 2 connector that link together the two board and re-solder the ground link both side. Re-assemble anything togheter with care, following the instuction given from the same link given above. Now try it, if you think it's still too hi, you can use any other capacitor value between 1k and 10 kpf (Low- Hi volume beep).
Good luck.

posted by alfred @ 22:04