Puzzling reception question

[Xterraxplorer]

Let me begin this by saying that I know little to nothing about circuit boards. I've had CB's for the last 20 years, but never worked on them. This is an area that I always paid someone to do. The issue is that my repair guy passed away four years ago, and the other guy in town is sketchy at best. I recently picked up a Midland 77-285 for $5 at a thrift store. I figured it was worth the money to play around with. I hooked it up last night and it makes a subtle whine while it is on. I turned the volume up, squelch down, and still received nothing. At this point I figured "what the heck" and keyed the mic. Once keyed, it began to receive static. I pulled the mic off to see if the keyway had broken and I hooked it up wrong, ie crossed pins, but no. I googled the problem and couldn't find a post to match what I had going on, nor can I seem to find a schematic for this radio. Would somebody point me in the direction of what to look at?

 

[4x4junkie]

You're saying the radio receives while you have the PTT pressed, but makes the whine while it's released?

If this is the case it's almost certainly a mis-wired microphone (or your mic is for the (much more common) 4-pin Uniden/Cobra/Galaxy configuration).

Schematic (also showing the mic) here.

Pin 1 = mic audio
Pin 2 = ground
Pin 3 = receive (speaker)
Pin 4 = PTT

 

[Xterraxplorer]

Thank you so much. I kinda feel like a bonehead for not knowing there was more than one setup for the four pins. Mine has Cobra stamped right on it. I feel like a bigger bonehead looking at the link you posted and realizing that I had been to the same page and overlooked the schematic. So again, thank you.

 

[Herbie]

Solved in 2 posts. Love this forum.

 

[Xterraxplorer]

Well it's not solved in two posts exactly. I managed to find the correct mic, I have static, but no chatter. I'll be checking it with a friend of mine tomorrow as I have no clue if I'm even transmitting.

 

[Xterraxplorer]

Okay, so I was able to test it out tonight, and I could receive but not transmit. For kicks, I took a look at the wiring on the mic and the red wire on pin 4 was disconnected. A quick solder job and now she is working like a champ. 4x4junkie, I appreciate it. :clapping: I probably would have bought another radio if you hadn't told me about the difference in wiring. Happy trails.

 

[4x4junkie]

Always glad to help (solving problems in as few posts as possible )

That Midland looks to be a nice radio, should be a keeper regardless of what you paid for it. Put a decent antenna on it (something 5' or taller) and you should be getting out pretty good with it.

 

[Xterraxplorer]

I've got a fire stick currently installed, but I might try my 102 again. I opted to mount the antenna on the front bumper and I am loving the location. My worry is smacking someone with it. My SWRs are pegged when I key in so I definitely need to adjust the antenna, and find a better power source.

 

[4x4junkie]

Yeah bumpers are about the worst place to mount an antenna (as your bad SWR shows)... A 102" whip can make the best of that location, but it's still far from ideal. Top of roof is best (I run a 5.5' Francis CB-26 Hot Rod w/spring on the roof of mine), but fender/hood mounts, and even quarter-panel or taillight bracket mounts are a hundred to thousand times better than a bumper mount.

 

[Xterraxplorer]

I'm not a huge fan of bumper mounts myself, but for what I'm doing it should work fine. I'm working on building a roof rack right now, and if I wind up not liking the location, I'll build a mount on the side of that. If I do like the location, I'll be incorporating a mount on the new front bumper whenever I finally get that.