Radioshack TRC-487

[nosaj]

Got a Radioshack TRC-487 When keyed up I get no audio. I also have it connected to a monitor scope so I can see modulated audio leaving the antenna jack. It received the weather band so the audio amplifier looks to be functional.
Cannot find a service manual on it . Cat number is 21-1594.
Any help would be much appreciated.

Thanks,
Jason

[51]

troubleshoot down the line block diagram style.check the mic first off, next check mic jack, wires, and board for problems. radioshack rigs are pretty robust so i would almost bet its just a mic and or mic wiring problem.

[nosaj]

So as far as jack wiring I should be ok following this service manual to inject audio? Looks like pin4 should be input.

Let just say I have a box full of misc cb stuff and matched up what I thought would be put together.
The mic and jack are a 5pin din. So to verify mic functioning I should be able to do a continuity test between pins 4 and 5 with it keyed.

But based on the monitor scope I know the mic is working as I can see the audio output on it's screen.
Thank,
Jason

[nosaj]

Also squelch has no effect just silent.
Jason

[MDYoungblood]

I'm not getting what your saying. The radio receives CB signal fine but there isn't any modulation when keyed? Is this right? Checking the microphone for continuity will just show the RX/TX switching is fine but not the mic element or the mic ground, RX/TX uses a separate ground. Possible problem could be the mic, the mic element, or the ALERT/WX/CB switch.

3's

Greg

[nosaj]

No as far as receive the only thing I can receive is WX that I can hear.
On other CBs you can turn squelch all the way down and hear static this one is silent no matter which way the squelch is moved.

Here's my setup trc-487 ANT line to Heatkhit HO-10 monitor scope then to ANT.

When I key up and speak into mic I can see the audio of my voice.

I have a magmount antenna on a 9ft long metal door setup as a table. Next week I should have a vertical put up.

How would one go about testing RX ? setup a second working CB or RF generator?
Thanks,
Jason

[51]

im with mdy, your posts are all over the place, the op said you have no audio, now you do have audio no receive? anyway all it is is a mic wiring issue. you said you just put a random mic on with the same connector, the mic is wired wrong,. you have all functions except rx, which is why no squelch,. radio shack radios are wired so the receiver audio is cut with no mic connected. (ie your wrong wired mic). rewire the mic problem solved.

[nosaj]

Rewire it to what?

[51]

find out what number pin does what on the radio (pin1-tx, pin2-rx, pin3-audio etc..) then find out what color wire does what on your mic (red-tx, black-rx, shield-ground etc...) then solder the correct mic wires to the correct mic plug pins. once the mic is wired correctly if it still does not work, there are more complex steps/tests that can be performed.

[MDYoungblood]

No as far as receive the only thing I can receive is WX that I can hear.
On other CBs you can turn squelch all the way down and hear static this one is silent no matter which way the squelch is moved.

Here's my setup trc-487 ANT line to Heatkhit HO-10 monitor scope then to ANT.

When I key up and speak into mic I can see the audio of my voice.

I have a magmount antenna on a 9ft long metal door setup as a table. Next week I should have a vertical put up.

How would one go about testing RX ? setup a second working CB or RF generator?
Thanks,
Jason

I think the receive problem can be contributed to your antenna setup, it is basically a tiny mobile setup with not much counterpoise, receiving will be compromised. I like the Heathkit HO-10, had one years ago, if it showing modulation it could be just a trace from the radios IF circuit on the shield on the coax. My would show another radio not even hooked up inline.Having another radio is always nice, I use and old Uniden Washington Base as a test radio, it is connected to a dummy load and I built a 5 mile attenuator for the receive, look it up, they are easily built.

3's

Greg

[nosaj]

find out what number pin does what on the radio (pin1-tx, pin2-rx, pin3-audio etc..) then find out what color wire does what on your mic (red-tx, black-rx, shield-ground etc...) then solder the correct mic wires to the correct mic plug pins. once the mic is wired correctly if it still does not work, there are more complex steps/tests that can be performed.

find out what number pin does what on the radio (pin1-tx, pin2-rx, pin3-audio etc..)
Not to be a moron, but what is a good suggestion on this? I have a sig gen I can use to input audio. I do know that either pin1 or pin5 carries 5vdc. Not sure on this 5pin din which is 1 and which is 5.

Thanks,
Jason

[MDYoungblood]

find out what number pin does what on the radio (pin1-tx, pin2-rx, pin3-audio etc..) then find out what color wire does what on your mic (red-tx, black-rx, shield-ground etc...) then solder the correct mic wires to the correct mic plug pins. once the mic is wired correctly if it still does not work, there are more complex steps/tests that can be performed.

find out what number pin does what on the radio (pin1-tx, pin2-rx, pin3-audio etc..)
Not to be a moron, but what is a good suggestion on this? I have a sig gen I can use to input audio. I do know that either pin1 or pin5 carries 5vdc. Not sure on this 5pin din which is 1 and which is 5.

Thanks,
Jason

I haven't a clue why you found 5vdc on any of the microphone pin numbers, that radio have just a standard dynamic microphone, this shows a replacement RS mic connections;


3's

Greg

[nosaj]

Is there a general guide for testing out cb mic's I have a bucket of them, and for one I would like to know what I can do to verify the mic is working. Can I hook it up to a oscilloscope(bench scope not the monitor scope) and just speak into the mic to register the element is good?
Thanks,
Jason

As a followup i put up a an-99 antenna got the swr just below 1.5 a bit. Daytime no cb reception rainy weather today, tonight fog and I'm receiving quite a bit but I think everyone is a bit too far for transmit.

[MDYoungblood]

I was getting a bunch of microphones recently from locals that needed repair so I ended up purchasing a tester form our forum sponsor with happens to be cheaper than ones on that auction site everyone uses;
[Please login or register to view this link]
If you have a lot of them and plan to sell them off that would be the way to go. I got the 3pin cord as well to hook it up to my bench supply.

3's

Greg

[51]

Is there a general guide for testing out cb mic's I have a bucket of them, and for one I would like to know what I can do to verify the mic is working. Can I hook it up to a oscilloscope(bench scope not the monitor scope) and just speak into the mic to register the element is good?
Thanks,
Jason

As a followup i put up a an-99 antenna got the swr just below 1.5 a bit. Daytime no cb reception rainy weather today, tonight fog and I'm receiving quite a bit but I think everyone is a bit too far for transmit.

the signal from a mic element is to low to trigger the oscilloscope.the quickest and easiest way to test microphones is with a multimeter.
isolation of all lines, continuity between tx and shield line switch in, continuity between rx and shield switch out, mic element continuity and impedance, and so on. very easy process