Uniden pc687 has no modulation and no sound for recieve on the speaker

Either your power supply is struggling to deliver enough current so when the speaker volume increases, the remaining power for the receiver decreases or the person transmitting has an over modulation problem.
If you turn your volume down and the needle stops bouncing, you may need to look at your power connections or have your radio serviced and set back up.

I have the schematic, in a pdf form. Just need a way to send it to you. email/ftp/ send me a self address envelope ill print it out its not very big.

You may have a dead meter.
Modulation is audio's affect on swing wattage or pep. Notice that needle moving more with your voice.
Dead key or carrier wattage is without your voice enhancing the power only with mic keyed.
I can only assume that the chipset you are referring to is an ic chip audio or pll which must be working if you are receiving audio.
Check your mic cord................ transmit and modulation and even your receive volume can be affected by the cord/mic plug solder joints or broken wires here.
http://www.cbtricks.com/radios/galaxy/dx33hp2/graphics/dx_33hp2_sch.pdf this is a similar radio the General Lee, Connex 3300hp and Galaxy hp2 share boards i believe dont hold me to that thou.

If the needle still moves while it is supposed to be receiving, check the speaker wires. This is the first and simplest thing to look at.

Wiring 1 4 pin D104 mic to a Uniden Grant CB is as follows -

• Pin 1 - Shield - Shield
• Pin 2 - Audio - White
• Pin 3 - Transmit - Red
• Pin 4 - Receive - Black

Regards, Tony

Could be audio chip.

• Insert external speak jack into pa port.
• Turn volume down
• Switch cb/pa switch to pa
• speak into mic

if you are getting audio from speaker ......chip is fine.

Sounds like bad external speaker

Sounds like you are not modulating well. try adjusting your amp.also, test your antenna for wire breakage and, make sure that your mic has good wires as well.

Either the mike or cable is bad or you have a problem in the transmit speech amplifier or modulator.

Can you hear static when the squelch is at minimum ?. If you can hear static then tere is nothing wrong with the audio system. If you are sure about the squelch, connect goosd speaker directly to the 2 wires coming from the main board bypassing the speker jack. if there is still no sound then the audio amp chip is defective. The audio amp can only be damaged if the output is shorted for a long period of time.