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Post by husker on Jan 12, 2018 22:46:49 GMT -5
Well.....Sandbagger is the man of the hour!! I pulled C133 the cap that feeds pin5, I figured I had one, why not, go ahead and replace it..and it works great now. Ran for almost 45 mins without a flaw. Great lesson, one little 50 cent part an bring a beautiful radio to it's knees!!!! THANK YOU!!!!!!! Hopefully it will stay working for you. But I have to wonder why the cap you already replaced once was bad. You usually don't see this with brand new parts. Guess what, ran great last night, turned it on tonight and the issue started to pop up again. I am very confused..
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Post by husker on Jan 12, 2018 23:25:01 GMT -5
when the issue happens now to the receive volume, the IC4 voltages are exactly where they should be. looks like the issue is further down the road. The s-meter moves, just no volume
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Post by husker on Jan 13, 2018 0:22:28 GMT -5
I was thinking since the S meter is moving, but no audio, I would check IC6. The voltages were strange .. Pin1 12.95vdc Pin2 6.86vdc (check c180?) Pin3 0 Pin4 0 Pin5 1.18vdc(check c179?) Pin6 1.18vdc Pin7 0 Pin8 0 Pin9 6.6vdc Pin10 13.71vdc
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Post by 2600 on Jan 13, 2018 0:46:02 GMT -5
I would have a look at C186. The original part would have been rated at 10 Volts. That alone makes it a "regular suspect" when receiver audio alone fails, leaving the S-meter still busy, and has no effect on transmit at all.
Original value is 220 uf. Anything from 100 to 330 would likely work the same.
73
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Post by husker on Jan 13, 2018 1:14:15 GMT -5
I would have a look at C186. The original part would have been rated at 10 Volts. That alone makes it a "regular suspect" when receiver audio alone fails, leaving the S-meter still busy, and has no effect on transmit at all. Original value is 220 uf. Anything from 100 to 330 would likely work the same. 73 Yup, that was one of the caps that was replaced with the kit, I reheated the connection to make sure I didn't have a cold joint. Still the same issue, the volume is there, just real soft, if I turn it all the way up it gets a bit louder. But if I turn it all the way down it stays the same low level. I only have 100uf caps, I can replace that one with a 100 to see if that makes a difference.
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Post by husker on Jan 13, 2018 1:45:32 GMT -5
No joy, replaced the cap as well, just to be safe. I did find a 220uf. Still weak audio
But remember I said there had been someone in this radio, c132 should be a .0047 50v cap, someone put in a 2.2uf 50v cap. Any clue why???
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Sandbagger
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Post by Sandbagger on Jan 13, 2018 10:37:06 GMT -5
I would have a look at C186. The original part would have been rated at 10 Volts. That alone makes it a "regular suspect" when receiver audio alone fails, leaving the S-meter still busy, and has no effect on transmit at all. Original value is 220 uf. Anything from 100 to 330 would likely work the same. 73 Yup, that was one of the caps that was replaced with the kit, I reheated the connection to make sure I didn't have a cold joint. Still the same issue, the volume is there, just real soft, if I turn it all the way up it gets a bit louder. But if I turn it all the way down it stays the same low level. I only have 100uf caps, I can replace that one with a 100 to see if that makes a difference. At this point, can you key the transmitter? The reason I ask is that pesky unlock circuit. C232 by way of TR53 will pull the audio nearly to ground and pretty much mute it if there is an unlock condition. It will also disable the ability to go into TX mode by way of TR35. There are two legitimate ways that the unlock circuit can be triggered. The first is if the channel selector is moved off of a channel detent (you may notice that the audio mutes as you spin the dial). The second is if the PLL becomes unlocked. Measure the voltage on pin 6 of IC1(MB8734). It should be at or close to 8V. If it's low, like <1V there is a problem somewhere in the PLL circuit. I've seen older 2000's with dirty channel selectors that if you simply bump them, the audio will mute momentarily. You might try jiggling the selector to see if that makes any difference. You can also try removing C232 and see if the audio returns. If it does and there seems to be no other indications of unlocking, there may be a problem with either the channel selector, TR53 or TR47. If it turns out that the selector is dirty, you can simply cut the trace that goes from the selector to the unlock circuit. It's really not that important.
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Sandbagger
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Post by Sandbagger on Jan 13, 2018 10:54:30 GMT -5
No joy, replaced the cap as well, just to be safe. I did find a 220uf. Still weak audio But remember I said there had been someone in this radio, c132 should be a .0047 50v cap, someone put in a 2.2uf 50v cap. Any clue why??? C132 provides a degree of filtering/smoothing for the SSB TX ALC circuit. Increasing the value will probably change the attack/decay time. Not sure why someone would do that. The factory value seems to work ok. Most people who "peak up" radios would simply defeat the ALC anyway (not a good idea).
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Post by husker on Jan 13, 2018 11:54:49 GMT -5
Thanks for the reply! Yes, it keys fine, power is set to 2.5 watts and swings to almost 5. And I did order that part to replace the cap that’s the wrong value. Not sure why they would replace a disk cap with an electrolytic cap. This is the third “golden screwdriver” item I have found. Still not sure about the diode off pin 10 of IC6. I will try the channel selector to see if it’s dirty. It does seem like it is locked , the volume is there, just muted.
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Post by husker on Jan 13, 2018 13:14:13 GMT -5
Yup, that was one of the caps that was replaced with the kit, I reheated the connection to make sure I didn't have a cold joint. Still the same issue, the volume is there, just real soft, if I turn it all the way up it gets a bit louder. But if I turn it all the way down it stays the same low level. I only have 100uf caps, I can replace that one with a 100 to see if that makes a difference. At this point, can you key the transmitter? The reason I ask is that pesky unlock circuit. C232 by way of TR53 will pull the audio nearly to ground and pretty much mute it if there is an unlock condition. It will also disable the ability to go into TX mode by way of TR35. There are two legitimate ways that the unlock circuit can be triggered. The first is if the channel selector is moved off of a channel detent (you may notice that the audio mutes as you spin the dial). The second is if the PLL becomes unlocked. Measure the voltage on pin 6 of IC1(MB8734). It should be at or close to 8V. If it's low, like <1V there is a problem somewhere in the PLL circuit. I've seen older 2000's with dirty channel selectors that if you simply bump them, the audio will mute momentarily. You might try jiggling the selector to see if that makes any difference. You can also try removing C232 and see if the audio returns. If it does and there seems to be no other indications of unlocking, there may be a problem with either the channel selector, TR53 or TR47. If it turns out that the selector is dirty, you can simply cut the trace that goes from the selector to the unlock circuit. It's really not that important. wow, ok...so I powered it up this morning, works fine. Typically takes a while at first to trigger the event. I jiggled the channel selector and it absolutely mimicked the issue. Can I clean it, or should I replace it? Not saying that is the issue, but I am learning one step at a time. Take to each variable so to speak. I dom't know yet if that is the issue until the problem happens. One strange thing, power on ch1 is 2.5 watts output, on channel 40 isnt's almost 3.5. My SWR's are under .5 across the board (using an SWR meter) what would cause the power difference? Ok, when the issue happens Pin1 of IC1 is 3.4vdc. (pin 1 is the pin by the little dot correct? Just making sure)
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Sandbagger
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Post by Sandbagger on Jan 13, 2018 13:47:39 GMT -5
At this point, can you key the transmitter? The reason I ask is that pesky unlock circuit. C232 by way of TR53 will pull the audio nearly to ground and pretty much mute it if there is an unlock condition. It will also disable the ability to go into TX mode by way of TR35. There are two legitimate ways that the unlock circuit can be triggered. The first is if the channel selector is moved off of a channel detent (you may notice that the audio mutes as you spin the dial). The second is if the PLL becomes unlocked. Measure the voltage on pin 6 of IC1(MB8734). It should be at or close to 8V. If it's low, like <1V there is a problem somewhere in the PLL circuit. I've seen older 2000's with dirty channel selectors that if you simply bump them, the audio will mute momentarily. You might try jiggling the selector to see if that makes any difference. You can also try removing C232 and see if the audio returns. If it does and there seems to be no other indications of unlocking, there may be a problem with either the channel selector, TR53 or TR47. If it turns out that the selector is dirty, you can simply cut the trace that goes from the selector to the unlock circuit. It's really not that important. wow, ok...so I powered it up this morning, works fine. Typically takes a while at first to trigger the event. I jiggled the channel selector and it absolutely mimicked the issue. Can I clean it, or should I replace it? Not saying that is the issue, but I am learning one step at a time. Take to each variable so to speak. I dom't know yet if that is the issue until the problem happens. One strange thing, power on ch1 is 2.5 watts output, on channel 40 isnt's almost 3.5. My SWR's are under .5 across the board (using an SWR meter) what would cause the power difference? Ok, when the issue happens Pin1 of IC1 is 3.4vdc. (pin 1 is the pin by the little dot correct? Just making sure) Pin 1 of IC1 is the VCO output. The voltage will change depending on which channel you are on. Pin 6 is the lock circuit output. I would not worry about replacing the channel selector. If the unlock section becomes unusable, you can simply disconnect it. As long as the pins that determine the actual channels are ok, then I would not worry about the switch. A difference in power output between channel 1 and 40 can be as simple as just needing an alignment. I would do that before looking into other causes. But I would test the power into a dummy load, just to make sure that any difference in SWR does not affect the wattmeter's reading.
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Post by husker on Jan 13, 2018 14:03:01 GMT -5
So what do you think my next step should be? I don’t have a dummy load, I use my antenna. Was that voltage on pin1 acceptable?
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Sandbagger
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Post by Sandbagger on Jan 13, 2018 14:55:48 GMT -5
So what do you think my next step should be? I don’t have a dummy load, I use my antenna. Was that voltage on pin1 acceptable? Pin 1 voltage is ok, depending on what channel you are on. It will rise the higher you go. I would be more concerned about what happens on pin 6 when the radio flakes out.
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Post by husker on Jan 13, 2018 15:22:12 GMT -5
Ok, I will check it when I get home. Need to run to Costco
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Post by husker on Jan 13, 2018 18:23:25 GMT -5
So what do you think my next step should be? I don’t have a dummy load, I use my antenna. Was that voltage on pin1 acceptable? Pin 1 voltage is ok, depending on what channel you are on. It will rise the higher you go. I would be more concerned about what happens on pin 6 when the radio flakes out. ok, so I power it up, the volume stays "hung" if you will at about 1/2 up. I can't turn it down, but I can make it a little louder if I turn it up. At the moment pin 6 is 8.1vdc
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Sandbagger
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Post by Sandbagger on Jan 13, 2018 18:26:56 GMT -5
Pin 1 voltage is ok, depending on what channel you are on. It will rise the higher you go. I would be more concerned about what happens on pin 6 when the radio flakes out. ok, so I power it up, the volume stays "hung" if you will at about 1/2 up. I can't turn it down, but I can make it a little louder if I turn it up. At the moment pin 6 is 8.1vdc That's starting to sound like a dirty volume control pot......
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Post by husker on Jan 13, 2018 18:44:17 GMT -5
ok, so I power it up, the volume stays "hung" if you will at about 1/2 up. I can't turn it down, but I can make it a little louder if I turn it up. At the moment pin 6 is 8.1vdc That's starting to sound like a dirty volume control pot...... Is it possible to clean it with contact cleaner?
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Sandbagger
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Post by Sandbagger on Jan 13, 2018 19:31:03 GMT -5
That's starting to sound like a dirty volume control pot...... Is it possible to clean it with contact cleaner? Absolutely!
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Post by husker on Jan 13, 2018 19:38:38 GMT -5
Is it possible to clean it with contact cleaner? Absolutely! it's been running like a champ for an hr so. I will clean it here in a bit. I do have a .005 disk cap to put c132 back to a closer value, but its a 500v one. Could I still use that? Or wait until the 59v volt part comes in? The original value is .0047 59v.
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Sandbagger
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Post by Sandbagger on Jan 13, 2018 22:00:41 GMT -5
it's been running like a champ for an hr so. I will clean it here in a bit. I do have a .005 disk cap to put c132 back to a closer value, but its a 500v one. Could I still use that? Or wait until the 59v volt part comes in? The original value is .0047 59v. The value of that part is not critical. You can always use a cap rated for a higher voltage, but never a lower one. The only issue might be the physical size of the higher value part not fitting in the board.
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Post by husker on Jan 13, 2018 22:12:52 GMT -5
it's been running like a champ for an hr so. I will clean it here in a bit. I do have a .005 disk cap to put c132 back to a closer value, but its a 500v one. Could I still use that? Or wait until the 59v volt part comes in? The original value is .0047 59v. The value of that part is not critical. You can always use a cap rated for a higher voltage, but never a lower one. The only issue might be the physical size of the higher value part not fitting in the board. Wow...I cleaned it real well, now it actually moves rather easily when I turn it. I have got it running again, this time it didn’t have the volume issue when I started the radio. Here’s crossing my fingers!
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Post by husker on Jan 14, 2018 0:08:43 GMT -5
it's been running like a champ for an hr so. I will clean it here in a bit. I do have a .005 disk cap to put c132 back to a closer value, but its a 500v one. Could I still use that? Or wait until the 59v volt part comes in? The original value is .0047 59v. The value of that part is not critical. You can always use a cap rated for a higher voltage, but never a lower one. The only issue might be the physical size of the higher value part not fitting in the board. OMG...................ok...so I figured out the issue I *think* because I can reproduce it. The "radio" side of my amp's coax connector seems to have a SHORT. I was moving all my radios etc. to a new bench. That's when the Cobra stopped working again. I keyed it and the meter (its on the out bound side of the amp) didnt move at all..So I connected the coax directly to the meter which then goes to my low pass filter. When I went direct and cut out the amp, everything works awesome. If I connect to the amp, the volume dies ... So now I need to try to see what the issue on the amp is!! lol, if its not one thing it's another!!!! So you guys know Kenrich 400's at all
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Post by husker on Jan 14, 2018 1:36:46 GMT -5
and that issue was just a broken solder connection to the coax connector! Simple fix for once!!!!
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Sandbagger
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Post by Sandbagger on Jan 14, 2018 10:56:04 GMT -5
and that issue was just a broken solder connection to the coax connector! Simple fix for once!!!! Intermittent coax connections can play havoc with both receive and transmit. Worse yet, they can make you think more serious issues are the culprit. Hopefully everything is ok now.
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Post by husker on Jan 14, 2018 17:24:32 GMT -5
and that issue was just a broken solder connection to the coax connector! Simple fix for once!!!! Intermittent coax connections can play havoc with both receive and transmit. Worse yet, they can make you think more serious issues are the culprit. Hopefully everything is ok now. No doubt! Guess I never would have thought to check the coax. But day two and still working perfect.
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Post by husker on Jan 15, 2018 0:52:06 GMT -5
and that issue was just a broken solder connection to the coax connector! Simple fix for once!!!! Intermittent coax connections can play havoc with both receive and transmit. Worse yet, they can make you think more serious issues are the culprit. Hopefully everything is ok now. Guess what.....after running all evening and most of today...it's back. And this time I think it is the channel selector..I think it is because when I change the channel there is no change in audio volume, it is muted. I jiggled it and the normal sound came back at times. Other times it doesn't come back. I pulled c232 and the result was zero audio. But I am pretty sure it is in the lock circuit. So how do I disable it?
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Post by husker on Jan 15, 2018 4:05:32 GMT -5
Also I read about replacing c179 with an electrolyte cap. Say 22uf by 25 volts. Ever heard of this?
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Sandbagger
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Post by Sandbagger on Jan 15, 2018 13:58:33 GMT -5
Intermittent coax connections can play havoc with both receive and transmit. Worse yet, they can make you think more serious issues are the culprit. Hopefully everything is ok now. Guess what.....after running all evening and most of today...it's back. And this time I think it is the channel selector..I think it is because when I change the channel there is no change in audio volume, it is muted. I jiggled it and the normal sound came back at times. Other times it doesn't come back. I pulled c232 and the result was zero audio. But I am pretty sure it is in the lock circuit. So how do I disable it? If you think the unlock circuit is kicking in, try keying the mic. if it still transmits, then the unlock circuit isn't the issue. If you lose receive audio, try modulating your transmit. If transmit modulation is still good, then the audio amp (IC6) is ok and the problem has to be further back in lower receive audio stages. Squelch circuit (dirty squelch pot?)?
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Post by husker on Jan 15, 2018 14:28:16 GMT -5
Guess what.....after running all evening and most of today...it's back. And this time I think it is the channel selector..I think it is because when I change the channel there is no change in audio volume, it is muted. I jiggled it and the normal sound came back at times. Other times it doesn't come back. I pulled c232 and the result was zero audio. But I am pretty sure it is in the lock circuit. So how do I disable it? If you think the unlock circuit is kicking in, try keying the mic. if it still transmits, then the unlock circuit isn't the issue. If you lose receive audio, try modulating your transmit. If transmit modulation is still good, then the audio amp (IC6) is ok and the problem has to be further back in lower receive audio stages. Squelch circuit (dirty squelch pot?)? 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.
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Sandbagger
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Post by Sandbagger on Jan 15, 2018 18:21:44 GMT -5
If you think the unlock circuit is kicking in, try keying the mic. if it still transmits, then the unlock circuit isn't the issue. If you lose receive audio, try modulating your transmit. If transmit modulation is still good, then the audio amp (IC6) is ok and the problem has to be further back in lower receive audio stages. Squelch circuit (dirty squelch pot?)? 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.
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