|MODIFYING A JINGTONG JT208 or JT308 HANDHELD FOR BETTER AUDIO|
As supplied from the factory, these otherwise excellent little radios have a bad defect. The transmit audio is unfortunately somewhat "muffled" (i.e. all of the audio high frequencies are missing) when the internal electret microphone is used. This is not surprising as the sound has to make its way to the internal mike via a very tortuous path which includes the speaker diaphragm. The problem is easily rectified by drilling a 2 mm diameter hole in the case which allows the trebles to reach the mike, BUT NOTE THAT DOING THIS WILL VERY PROBABLY VOID YOUR WARRANTY. IT IS ENTIRELY YOUR RESPONSIBILITY IF YOU DO THIS MODIFICATION.
This problem can be overcome entirely in another way, by purchasing and using the optional hands free setup. This has no warranty implications, and is probably a very good idea because it moves 2.5 watts of RF output away from whatever remaining brain matter you may possess, probably downward on to your belt where it will produce possibly desireable short term sterilization effects. (The resulting audio is excellent.)
Anyway, if you are a committed mobile phone user, the damage is probably permanent and so here is the mod procedure...................
There are two ways of producing a hole in the front panel, and neither is without risk. First, using the details supplied in the following photo, you can directly drill through the front of the rig, without disassembling it. This carries the risk that if you are hasty and careless, when the drill breaks through the plastic front panel, it will drill into and destroy the electret mike. If you elect to use this procedure, either spin the 2mm dia. drill directly with your fingers, or mount it in a pin vice and use your fingers to spin that. Do not put the drill bit into a power tool, as the chances of doing damage will be enormously magnified. It will be found that the plastic used for the case is very soft and only around 1mm thick, and that only very gentle pressure and a little patience are required to produce a neat 2mm hole. It is very easy to feel when the drill is about to break through when this approach is used, and thus avoid doing damage.
If you are unhappy with this simple procedure (developed by Dean VK5LB- thanks Dean!!) then you will have to disassemble the transceiver. (The routine following is also useful if transceiver repairs must be done) This procedure carries the risk of fatigueing through the wires that connect the speaker and battery to the mainboard, and/or doing damage to the mainboard itself with its delicate surface components, so be careful!!
CAREFULLY VACUUM AND WASH THE AREA OF YOUR BENCH WHERE YOU WILL WORK TO TOTALLY CLEAN IT OF ALL PARTICLES AND RUBBISH (WHEN YOU GET THE RIG OPEN YOU WILL SEE WHY!)
1. Unscrew the rubber duck aerial, and remove the two knobs by pulling vertically away from the case. Remove the clipped in Nicad battery and unscrew the belt mounting clip (if fitted).
2.Carefully remove the thin flexible plastic moulding at the case top by first gently prising upwards and outwards at a corner as shown in the photo. A small screwdriver with a thin flat and relatively blunt 3mm wide blade is an excellent aid here ( a blunt blade with rounded polished corners will prevent any damage to the moulding). Once a corner has been lifted use your fingers to complete the removal.
3. Pop the transmit switch rubber overlay out, by pushing parallel to the case side so that the rubber is released from the retaining T grooves in the side of the moulding.
4. Remove the case moulding above the battery compartment containing the retaining nuts for the belt clip. This is accomplished by gently prising outward alternatively on either side of the case at the joint line to release this moulding from the arrow headed snap clips moulded into the other half of the case. Both sides of the moulding on either side of the transmit switch hole have to be released. BE GENTLE AND CAREFUL !!!!!!!!!!
5. Remove the rubber cover over the plug for the hands free mike/earpiece assembly.
6. You now have before you the diecast chassis trapped within the front panel moulding. Note the two retaining protusions on the diecasting which fit into the plastic front panel moulding at the bottom of the battery compartment. The diecast chassis is removed from the front panel moulding by hingeing the aerial/potentiometer end of the diecast chassis outwards around these two retaining protusions. Insert two small screwdriver blades at the points indicated in the photographs and GENTLY spread the case sides apart to release the diecast chassis. WATCH WHERE YOU PUT THE SCREWDRIVER BLADES, TAKING GREAT CARE TO CAUSE NO DAMAGE TO THE PCB AND ASSOCIATED ELECTRONICS.
7. In the centre of the well provided in the front panel moulding for the microphone, drill a 2 mm dia hole. Deburr the hole on both sides using a sharp larger diameter drill (around 5mm dia) and then carefully clean the case to remove any loose particles (which can wreck the operation of the front panel switches).
8. Reassemble the unit using the reverse of the procedure outlined above. Gentle warming (warm to the touch) of the plastic moulding at the top of the case around the pots/aerial connector will cause the plastic to become quite pliable and thus easy to re-install. A hairdryer used cautiously , (so the plastic is NOT overheated) is a good aid here.