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Post by husker on Jan 15, 2018 19:26:18 GMT -5
I will clean the squelch as well, and yes, I can transmit and it shows out bound audio just fine ( the watt meter and modulation meter both move). But the muted audio mimic the sound of changing channels using the channel selector. When the flacky issue pops up, if I turn the channel selector knob, there is no change in noise in other words it is muted. Have you ever heard of the C179 thing before? Replacing the tantalum with an electrolytic? I am also going to try using headphones just to see what that does. Coincidentally (or not so), C179 is the 2.2uF tantalum cap that fails in the Cobra 138/139XLR, and replacing that with an electrolytic is recommended. So I'm thinking that you've got that mixed in with info for the Cobra 2000, so I don't think that applies here. Actually no, lol, it was a post where a guy had lost his audio. I mean, at this point what do I have to lose? |
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Post by husker on Jan 15, 2018 19:31:53 GMT -5
here is the post..
Need a little Help here... My cobra 2000 all of a sudden stopped receiving or tx on AM
Check C174, 175, 179, and 181 for shorted/leaky. My guess is that it's C179. If it's bad, replace it with an electrolytic cap, not a tantalum. Good luck & 73s.
his answer
he audio problem is fixed c179 fixed it.....
Don't know if it will help, but i am kind of at my wits end here. The strange thing is my radio has a tantalum in it, but the service manual says it should be electrolytic
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Sandbagger
Administrator/The Boss 
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Post by Sandbagger on Jan 15, 2018 19:56:01 GMT -5
Coincidentally (or not so), C179 is the 2.2uF tantalum cap that fails in the Cobra 138/139XLR, and replacing that with an electrolytic is recommended. So I'm thinking that you've got that mixed in with info for the Cobra 2000, so I don't think that applies here. Actually no, lol, it was a post where a guy had lost his audio. I mean, at this point what do I have to lose? Not much, but when you consider that the audio amp IC is also used for transmit modulation, and that seems to be working, I have a hard time believing that that cap would cause receive audio issues but not transmit modulation as well. |
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Post by husker on Jan 15, 2018 20:19:54 GMT -5
Actually no, lol, it was a post where a guy had lost his audio. I mean, at this point what do I have to lose? Not much, but when you consider that the audio amp IC is also used for transmit modulation, and that seems to be working, I have a hard time believing that that cap would cause receive audio issues but not transmit modulation as well. Lol, oh sure just destroy my idea  . Any other thoughts about this thing? I really don’t want to toss it in the scrape heap |
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Sandbagger
Administrator/The Boss
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Post by Sandbagger on Jan 15, 2018 22:25:49 GMT -5
Not much, but when you consider that the audio amp IC is also used for transmit modulation, and that seems to be working, I have a hard time believing that that cap would cause receive audio issues but not transmit modulation as well. Lol, oh sure just destroy my idea . Any other thoughts about this thing? I really don’t want to toss it in the scrape heap How about something REALLY simple? Have you tried a different microphone? Maybe the receive wire is intermittent. Simple thing #2 Check the speaker switch. My 2000 has a dirty switch and occasionally I have to jiggle it to get full speaker connection. Simple thing #3 Check speaker wire/jack/plug. Am intermittent there can cause the volume to cut out. |
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Post by husker on Jan 15, 2018 22:32:35 GMT -5
Lol, oh sure just destroy my idea . Any other thoughts about this thing? I really don’t want to toss it in the scrape heap How about something REALLY simple? Have you tried a different microphone? Maybe the receive wire is intermittent. Simple thing #2 Check the speaker switch. My 2000 has a dirty switch and occasionally I have to jiggle it to get full speaker connection. Simple thing #3 Check speaker wire/jack/plug. Am intermittent there can cause the volume to cut out. 1. Yup, I tried that today just for the heck of it. 2. Yup, I even tried a set of headphones. No difference 3. Yup, again tried a headphones which if I am reading that right comes before the speaker jacks correct? How about the squelch circuit?? Could that be drawing down the audio? |
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Post by husker on Jan 15, 2018 23:34:28 GMT -5
Lol, oh sure just destroy my idea . Any other thoughts about this thing? I really don’t want to toss it in the scrape heap How about something REALLY simple? Have you tried a different microphone? Maybe the receive wire is intermittent. Simple thing #2 Check the speaker switch. My 2000 has a dirty switch and occasionally I have to jiggle it to get full speaker connection. Simple thing #3 Check speaker wire/jack/plug. Am intermittent there can cause the volume to cut out. So tonight I figured it was time to re check all the voltages. Seems pin 2 in the audio chip is way to high. It should be 2.94, its reading 6.85 during the actual volume issue. And guess what..NO PA at all....so it *appears* the 7222 is bad? |
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Sandbagger
Administrator/The Boss
Posts: 6,247
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Post by Sandbagger on Jan 16, 2018 16:00:16 GMT -5
How about something REALLY simple? Have you tried a different microphone? Maybe the receive wire is intermittent. Simple thing #2 Check the speaker switch. My 2000 has a dirty switch and occasionally I have to jiggle it to get full speaker connection. Simple thing #3 Check speaker wire/jack/plug. Am intermittent there can cause the volume to cut out. So tonight I figured it was time to re check all the voltages. Seems pin 2 in the audio chip is way to high. It should be 2.94, its reading 6.85 during the actual volume issue. And guess what..NO PA at all....so it *appears* the 7222 is bad? Normally, I would agree with your deduction. But if you are truly getting proper transmit audio, there has to be something else playing games in there. If that IC was really bad, it wouldn't work in any mode. |
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Post by 2600 on Jan 16, 2018 16:01:08 GMT -5
What does pin 9 read?
Most of the time if this chip is bad, pin 9 will read wrong. Should be very close to one-half the supply voltage feeding into pin 1.
73
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Post by husker on Jan 16, 2018 16:08:22 GMT -5
What does pin 9 read? Most of the time if this chip is bad, pin 9 will read wrong. Should be very close to one-half the supply voltage feeding into pin 1. 73 Pin 1 is 12.98 Pin 2 is 6.85 Pin 3 is 0 Pin 4 is 0 Pin 5 is 1.21 Pin 6 is 1.21 Pin 7 is 0 Pin 8 is 0 Pin 9 is 6.6 Pin 10 is 13.71 I have a question though, in the schematic, it shows pin 2 should be 2.94 and mine is way higher. |
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Post by husker on Jan 17, 2018 9:11:15 GMT -5
What does pin 9 read? Most of the time if this chip is bad, pin 9 will read wrong. Should be very close to one-half the supply voltage feeding into pin 1. 73 I think at this point I have gone as far as I can go with my limited skill set. I either need to send it to someone to fix or dispose of it by selling the parts. Does anyone know a good tech I can send it to? I know 2600 doesn't do "mail in work" so I am looking for any recommendations please for a good tech. Thanks guys for all your help! |
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Post by husker on Jan 24, 2018 16:15:11 GMT -5
So I finally gave up and sent the radio to Greg Barkett in hopes of getting this thing fixed once and for all. It ran three days without a hitch in his shop. So that means the issue is somewhere on my end?
I tested my antenna system by connecting to other radios, they have no issues, I tried two different mikes (knowing how the 2000 could ground the receive circuit on a bad mike or wire/connection, I figured trying a second mike to make sure the one I had wasn't bad) and I still had the issue. So Greg is doing an alignment now and boxing the radio up. Like he said, if he can't get it to fail, he can't fix it. Yea, I certainly get that lol.....sigh
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Post by riveratmike on Jun 1, 2023 20:31:04 GMT -5
I have the same issue with my Cobra 2000. It got the golden screwdriver sometime in the late 80's. I purchased this radio from a friend in May of 2023. It does work good. TR24 was cut, R131 was cut and now I'm noticing VR11 and VR12 are missing and a 2.2uf electrolytic cap is in place of a .0047uf 50v ceramic cap at loc R132. It has a variable power output on the tone control for AM only. I want to get this radio back to stock condition but now I have to locate 2 variable resistors somewhere.
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Post by 2600 on Jun 1, 2023 23:27:42 GMT -5
Uh, "R132"?
Or "C132"?
If it's C132, that's a production change, and the correct component value really is 2.2uf. When C132 fails, it will make the sideband transmit audio "choppy" if the mike gain is turned up at all. If you substitute a .0047uf cap in that spot, you'll hear what I mean by "choppy" if you have another radio on hand to monitor the audio. You really need VR11 if you plan to use sideband. And if you don't, maybe not so much. VR11 sets the peak power limit for sideband transmit. You really need to keep the radio below the overdrive level in sideband transmit. Not only will it sound bad, but it can overheat the driver and final, reducing the service life.
VR12, not so much. It controls max AM modulation level, and AM is not so touchy about limiting the audio level as sideband is.
If you reconnect R131 without installing VR12, this will normally kill all your AM transmit audio dead as a post.
73
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Post by riveratmike on Jun 1, 2023 23:52:11 GMT -5
thanks for that info, yeah I meant C132. The radio is working good. AM power is at about 7 watts, but the SSB power is a little on the low side. It's only putting out about 10 watts on my watt meter. I need to get VR11 back in there.
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Post by 2600 on Jun 2, 2023 23:30:20 GMT -5
Depending on the type of wattmeter, that may be all you'll see on normal speech. How much power do you see with a whistle in to the mike with the gain full up?
73
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. Any other thoughts about this thing? I really don’t want to toss it in the scrape heap
