that thing as you called it is a disk capacitor. that is factory. one thing I did see in the pitures is a resister to ground on the solder side just under the transformer location. it does not hit me as a regular part. lift one leg of it to see if it kills the talk back. if not not sure what it is for. so remember the solder location and like I said just lift one leg. you can always solder it back as long as you make sure to see where it is at. looks to be soldered to the input leg of one of the audio plugs and it goes to ground could cause the talk back feature.
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Cobra 148 GTL Common Mods Question
- Thread starter crash-harris
- Start date
Ha! I just put the radio back in the truck and tested it. If that's the talkback, that's fine with me since it seems to be working fine with the talkback when I rear it a few moments ago.
Got power restored to the old scratchy Uniden and set my external speaker in the cab of the truck it's in (2 vehicles down from the truck with this Cobra 148 GTL). Had it switched to channel 19 and walked over to the trick with the Cobra and keyed a test and could hear myself in the Uniden's external speaker. Talkback on the Cobra is the same volume regardless of what happens to the knobs, so I'm treating it about like the Uniden and adjusting the Dynamike to avoid feedback. This test was done with the 4-pin Diesel 4-3 mic, right angle and 4 to 5 pin adapters in place.
I'm pretty sure I got the plug on the 5 pin mic wired correctly, but it looked like 2 wires on the PTT switch had been reversed and it wouldn't send or receive. I'll have to reverse those later so I have a mic for reference in the future.
Got power restored to the old scratchy Uniden and set my external speaker in the cab of the truck it's in (2 vehicles down from the truck with this Cobra 148 GTL). Had it switched to channel 19 and walked over to the trick with the Cobra and keyed a test and could hear myself in the Uniden's external speaker. Talkback on the Cobra is the same volume regardless of what happens to the knobs, so I'm treating it about like the Uniden and adjusting the Dynamike to avoid feedback. This test was done with the 4-pin Diesel 4-3 mic, right angle and 4 to 5 pin adapters in place.
I'm pretty sure I got the plug on the 5 pin mic wired correctly, but it looked like 2 wires on the PTT switch had been reversed and it wouldn't send or receive. I'll have to reverse those later so I have a mic for reference in the future.
talk back would be fixed if the resister is what they used for it. a little different from what I have seen in the past. is the desil mic a noise canceling mic. talk back works best if you have the noise canceling mic and you do not have to turn down the mic gain to stop the squeal.
The diesel mic is indeed a noise canceling mic. I have one connected to the Uniden as well, but I've always had to turn the mic gain down even with the Diesel 4-3's, just not as much.
As for the talkback, there's no resister between the CB and PA jacks on either side of the board. If it's been modded as you said near the transformer, then that's fine. I like having the talkback for diagnosis. If I find out its causing a problem I'll remove it later.
As for the talkback, there's no resister between the CB and PA jacks on either side of the board. If it's been modded as you said near the transformer, then that's fine. I like having the talkback for diagnosis. If I find out its causing a problem I'll remove it later.
I only saw the resister in a different location from what most people do the mod between the jacks. that is why I mentioned to unhook one leg of the resister to see if it killed the talk back. if you like the talkback thats fine. was just answering you question about the talk back. a resister from the audio to ground will give you talk back just like the resister between the 2 jacks.
I sure appreciate it.
I would pull one leg to test it if I didn't just put it back in the truck, and maybe had a desktop setup to test a CB on (garage isn't finished/this truck is too big for it and it's basically winter here in OH).
I would pull one leg to test it if I didn't just put it back in the truck, and maybe had a desktop setup to test a CB on (garage isn't finished/this truck is too big for it and it's basically winter here in OH).
The serial number starts with the digit "7". This suggests either 1977 or 1987 production year. The PLL chip will have a four-digit number that starts with either "76", "77", or "87", followed by two more digits that range from "01" to "52".
That might settle which decade it was made.
If it's really almost 40 years old, there may be some age issues to consider. Even if it's only 29 years old, replacing a handful of 10-Volt electrolytic capacitors could save you the "10-Volt Blues". Blown speaker and audio chip, loss of receiver (only) audio, loss of transmit audio only, or loss of all transmit, or loss of half your transmit power.
Each of those symptoms comes from the failure of a 10-Volt electrolytic cap in that circuit.
Kinda depends on mileage. The lower the odometer reading, the more service life is usually left on that sort of stuff.
After three or more decades, nothing electronic is maintenance free.
73
That might settle which decade it was made.
If it's really almost 40 years old, there may be some age issues to consider. Even if it's only 29 years old, replacing a handful of 10-Volt electrolytic capacitors could save you the "10-Volt Blues". Blown speaker and audio chip, loss of receiver (only) audio, loss of transmit audio only, or loss of all transmit, or loss of half your transmit power.
Each of those symptoms comes from the failure of a 10-Volt electrolytic cap in that circuit.
Kinda depends on mileage. The lower the odometer reading, the more service life is usually left on that sort of stuff.
After three or more decades, nothing electronic is maintenance free.
73
- No one is chatting at the moment.
...runna pile-up on 6m SSB