Just got the radio i was having issues tuning people in on ssb plus the freq counter has it's 92.2000 issues that aside i started the alignment of the synthesizer section form service manual 1st 3 steps went well and showed what was supposed to be there next step went off some where in outer space it was:
input of freq counter to tp10 radio on ch1 am look for .790MHz I get 3.050 MHz?
Next step was input of freqc to tp3 ch19 usb adjust ct2 for 7.801 MHz mine was 29.620 and bouncing?
next step LSB look for 7.7985 mine was 24.620 bouncing around ?
next step was input of freqc to tp14 ch19 am xmt adjust L31 for 7.8000 Mhz mine was jumping form 15MHz to 16 Mhz?
Using the L's and CT's shown i could not bring it into specs.
Any ideas on whats up with this radio would be welcomed.
P.S. It does transmit watts out are ok and receive audio is ok freq counter hooked to dummy load show it is off freq on am example ch1 27.050.
CObra 2000gtl issues
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redlght
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TheCBDoctor
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Hi redlght
The first question I have is, are you sure you don't have a problem with your test equipment? Is the probe you are using good? I ask this because if your test probe has too much capacitance it will throw off any readings. The test points are high impedance circuits and any stray capacitance will interfere with your readings. A times 10 probe will reduce the capacitance to 3 pfd.
When set at unity gain (1 to 1) the capacitance of the probe can be as high as 22 pfd. It seems that every thing you are measuring is twice what the value should be. I am concerned with TP-10. This is the feedback loop frequency that corrects the DC voltage from the PLL to the varactor diode.
A circuit may be over-driven which will cause secondary harmonics to double in value. I doubt this the case. Since you are not the original owner it is hard to say what the previous owner had done to the radio. Does the radio have channels? Has a coil been placed in series with the varactor diode? What modifications have been made to the radio?
I am very familiar with the Cobra 2000 GTL. I have never had readings like the ones you are getting. If the readings you are getting are true readings the radio should go out of lock and the Tx circuit would kick in the Tx inhibitor. It would be nice if you had a counter on the radio that did not have a bad microprocessor. Whenever you get a reading of 92.2000 MHz on the radio's counter that means the counter is free running. If you can install a working counter that would help you a lot in figuring out exactly what is wrong with the radio. By the test measurements you are providing the radio should not even be working.
So the first thing you should do is make sure your test probe is working. Are you using a good frequency counter and a test probe for an oscilloscope? You can not use a straight set of wires connected to the counter; you must you an oscilloscope probe with a times 10 function. I say this because your radio should not be working with those frequencies; it would be impossible because the math does not add up and the radio would be Out-Of-Lock and shut down.
I have worked on thousands of 2000's for nearly 3 decades. If I can be of any help I will certainly give it a try. Please post on the open forum so that others may have an input. At this point I would say it is the test equipment that is in error from what I have gathered.
Here is a link to my website in regards to the Cobra 2000 GTL:
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Respectfully,
The first question I have is, are you sure you don't have a problem with your test equipment? Is the probe you are using good? I ask this because if your test probe has too much capacitance it will throw off any readings. The test points are high impedance circuits and any stray capacitance will interfere with your readings. A times 10 probe will reduce the capacitance to 3 pfd.
When set at unity gain (1 to 1) the capacitance of the probe can be as high as 22 pfd. It seems that every thing you are measuring is twice what the value should be. I am concerned with TP-10. This is the feedback loop frequency that corrects the DC voltage from the PLL to the varactor diode.
A circuit may be over-driven which will cause secondary harmonics to double in value. I doubt this the case. Since you are not the original owner it is hard to say what the previous owner had done to the radio. Does the radio have channels? Has a coil been placed in series with the varactor diode? What modifications have been made to the radio?
I am very familiar with the Cobra 2000 GTL. I have never had readings like the ones you are getting. If the readings you are getting are true readings the radio should go out of lock and the Tx circuit would kick in the Tx inhibitor. It would be nice if you had a counter on the radio that did not have a bad microprocessor. Whenever you get a reading of 92.2000 MHz on the radio's counter that means the counter is free running. If you can install a working counter that would help you a lot in figuring out exactly what is wrong with the radio. By the test measurements you are providing the radio should not even be working.
So the first thing you should do is make sure your test probe is working. Are you using a good frequency counter and a test probe for an oscilloscope? You can not use a straight set of wires connected to the counter; you must you an oscilloscope probe with a times 10 function. I say this because your radio should not be working with those frequencies; it would be impossible because the math does not add up and the radio would be Out-Of-Lock and shut down.
I have worked on thousands of 2000's for nearly 3 decades. If I can be of any help I will certainly give it a try. Please post on the open forum so that others may have an input. At this point I would say it is the test equipment that is in error from what I have gathered.
Here is a link to my website in regards to the Cobra 2000 GTL:
[Please login or register to view this link]
Respectfully,
Respectfully as always,
Rick
Rick
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redlght
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Another problem it has tx and rx do not match others can hear me fine but i can not tune them in with the clarifer and my ch40 is 27.409 i can tune it higher but not lower to 27.4050
Wednesday, 27 March 2013, 18:14 PM
As far as i can tell the radio is not modded the clarifier is still locked no extra channels
Wednesday, 27 March 2013, 18:23 PM
another thing i found was input of dc meter to TP 9 ch 40 am adjust L19 to read 3 volts then check for aprox 2 volts on ch 1 when set to 3 on 40 channels 1 to 8 will either not tx or will for lack of a better term motor boat like hearing a bad plug wire coming over the radio but on tx and the rf meter will vibrate slightly if i kick it back up a tad on voltage all the channels tx.
Wednesday, 27 March 2013, 18:14 PM
As far as i can tell the radio is not modded the clarifier is still locked no extra channels
Wednesday, 27 March 2013, 18:23 PM
another thing i found was input of dc meter to TP 9 ch 40 am adjust L19 to read 3 volts then check for aprox 2 volts on ch 1 when set to 3 on 40 channels 1 to 8 will either not tx or will for lack of a better term motor boat like hearing a bad plug wire coming over the radio but on tx and the rf meter will vibrate slightly if i kick it back up a tad on voltage all the channels tx.
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TheCBDoctor
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Hi redlight,redlght wrote:Another problem it has tx and rx do not match others can hear me fine but i can not tune them in with the clarifer and my ch40 is 27.409 i can tune it higher but not lower to 27.4050
Now that makes sense. If you can find a working counter for the Cobra 2000 GTL that will help you a lot. The radio is not tracking. What modifications were done to the radio that you can see? Double check the first part of the alignment procedure. It is late, but I will get back to you tomorrow with some suggestions.
The reason the radio does Tx is because the radio is not Out Of Lock. Check the voice-lock modification. The DC output of the PLL that goes to the varactor diode is changing when you unkey. A working counter for the 2000 will show you this.
Until Thursday
Respectfully as always,
Rick
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redlght
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Will do doc thanks a ton for your help I have seen your site before i posted this I bow to your knowledge, i would like to fix the counter it has if possible, and it is not yet have the tech bulletin service done to it yet I can not detect any mods done the radio at all I also do not have your years of back ground with them either so i may have missed something but i will look deeper.
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TheCBDoctor
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redlght wrote:Will do doc thanks a ton for your help I have seen your site before i posted this I bow to your knowledge, i would like to fix the counter it has if possible, and it is not yet have the tech bulletin service done to it yet I can not detect any mods done the radio at all I also do not have your years of back ground with them either so i may have missed something but i will look deeper.
Hi Redight,
Fixing the counter will take up most of your time and it is unlikely to able to be fixed if the CPU (IC-506 TC5032P) is N/G. They tend to fail and are nearly impossible to find. Any counter you may use as scrap will probably have the same failure. You can find them reconditioned on eBay for $75. I don't know how the company is doing it, but they take yours in as part of the deal.
Calibrating TP-3 CT-2 to 7.8015 MHz: TP-3 L30 77980 MHz: TP-14 7.8000 MHz is critical and must be within 5Hz (Plus or Minus). It is important that you know your test counter, and probe are working, and capable of doing the job. The input impedance of the test probe should be 5 pfds or less. An oscilloscope probe with a x10 probe is best.
Buying a working 2000 counter will help you align the radio. Using a capable, properly tested frequency counter, place the voice-lock at 12 0'clock: align CT-2, L-30, and TP 14 within 5 Hertz; do this first. Then align L-23 AM, L-59 USB L-22 LSB using the radio's new frequency counter. If your Voice-lock is opened, and you want it to align at top dead center after it is done, do the following.
I measure the output of the radio's Tx; I use channel 20 @ 27.2050 MHz. Using your test probe, place the voice-lock in a position that will give you 27.2050 MHz... while keying up. I then adjust the variable cap next to the counter's reference crystal using a non-metallic screwdriver to match 27.205 MHz on the counter's display; now I have a reference point. Un-key the Mic.
Put the Voice-Lock at top dead center and Adjust L-23, on AM, until the Cobra 2000 display reads 27.205 on channel 20. Then adjust LSB L-59 to read the same. Do the same for L-22 USB. You will find that you may have to bottom-out L-59 to come close to 27.2050MHz. If moving the Voice-Lock a bit isn't a problem after it is done,then I would not worrying about that. If you are at 27.2490 MHz you may get a way with filing off about 1/16'" or less from the inductive tuning slug. Sometimes this will work. or replace the 11.3250 MHz loop crystal with an 11.3258 MHz. This will definitely work. You can find them in an older Cobra 148 GTL.
Summary:
1) Find a Cobra 2000 counter that works.
2 Make sure the test equipment is capable of doing the job and is working. Low impedance probes interfere with your test.
3) Adjust your Cobra counter using the radio's output. You may get a reading without actually touching the antenna output. It normally doesn't hurt the test EQ, but why take chance if you can get a reading by touching the wire shield instead? I found that placing the ground for the probe at the case ground, chassis ground (Any I.F. can), or no ground at all, will give you the best results depending on you test EQ.
4) With the Tx OFF, and the voice-lock centered: Adjust L-23 AM, then L-22 LSB, and L-59 USB (Last).
I am curious about the the reading for your feedback signal at .790 MHz (790 KHz)? A close to normal signal must be there for you to transmit on frequency. You can adjust the Tx (only) L-22, L-23, L-59 no matter what CT-3, L-30. and L-31 are. The latter adjusts both Tx and Rx; that is why they should be done first, and they are critical (+/- 5 Hertz).
Double check your test EQ. If the readings you say are correct, then that radio should not be transmitting
Since the counter isn't working you have nothing to lose; You may try resoldering the entire board keeping in mind that it is a double sided clad board. This repair works 15% of the time. The connections become old, so check for continuity on both sides of the board. Hey, you never know.
Keep me up to date. Try my method; in my opinion they got the alignment procedure backwards. I always felt it was in the wrong order after my first few alignments. I also found it is much easier with a working Cobra 2000 GTL frequency counter. Using this method I have cut the alignment time by more than half, and I know the radio will work better because you are starting at the radio's own reference point......its transmit output frequency.
Trade Secret:
Good luck,
Respectfully as always,
Rick
Rick
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redlght
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I have access to some TC5032P chips the double sided plate through boards I am familiar with re capping older sony 8mm video walkmans/ As far as adjustments L23 can not be turned enough either way to get to to where it needs to be like it no longer has the range to tune it in. Really none of the L's can be tuned to what they need to be like maybe I have a coupling problem some where? that affects tx and rx. More to come later on it. Thanks doc
P.S. I have noticed one mod D52 and D75 right next to the xtal either have been clipped and re joined or possibly replaced clipped and joined back together.They are black with orange colored bands not sure if those are originals or not.
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Sunday, 31 March 2013, 17:51 PM
Happy Easter to all. After some thinking on why the L's won't do much adjusting I went low tech and did deeper voltage checks. The pll pin that should have 8 volts sitting on it from D31 had fluctuating voltage seems it was broke off at the top of board and varying the voltage as I was testing.
I soldered a pin up through and to the pll pin things started to look up not done doing the alignments yet but way better results now. You are right on that L59 to the bottom I have not tried shaving it yet. I do how ever want to change over the pll to a mb8719. Any tips would be great. Many thanks Doc I am sure i'll have more questions as i go on.
Monday, 01 April 2013, 9:29 AM
Since i have not recapped it yet I wonder if C84 has leaked and that is what eroded the PLL pin, I did nto really see any signs of tampering. I seen it many times in old sony gv models of video walkmans the surface mount caps around year 10 to 15 would start to leak and eat plate through holes and such. Doc ever seen this in 2000's?
P.S. I have noticed one mod D52 and D75 right next to the xtal either have been clipped and re joined or possibly replaced clipped and joined back together.They are black with orange colored bands not sure if those are originals or not.
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Sunday, 31 March 2013, 17:51 PM
Happy Easter to all. After some thinking on why the L's won't do much adjusting I went low tech and did deeper voltage checks. The pll pin that should have 8 volts sitting on it from D31 had fluctuating voltage seems it was broke off at the top of board and varying the voltage as I was testing.
I soldered a pin up through and to the pll pin things started to look up not done doing the alignments yet but way better results now. You are right on that L59 to the bottom I have not tried shaving it yet. I do how ever want to change over the pll to a mb8719. Any tips would be great. Many thanks Doc I am sure i'll have more questions as i go on.Monday, 01 April 2013, 9:29 AM
Since i have not recapped it yet I wonder if C84 has leaked and that is what eroded the PLL pin, I did nto really see any signs of tampering. I seen it many times in old sony gv models of video walkmans the surface mount caps around year 10 to 15 would start to leak and eat plate through holes and such. Doc ever seen this in 2000's?
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TheCBDoctor
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Hi redlght
If D-75 and D-52 were cut then the radio's voice-lock was opened. Resolder D-75; it in is series with D-52. D-52 is cut when the voice lock is unlocked. Adjusting VR-5 will set the Tx frequency. If the voice-lock was unlocked then VR-5 is disabled. It sounds like someone had the voice-lock unlocked, and then put it back to factory.
With the voice-lock opened (Unlocked) the clarifier (Voice-Lock) will cause both Tx and Rx to deviate from frequency and track together. If your Voice-Lock is factory and locked that would explain why Tx and Rx will not track. With the voice-lock opened the voltage on Pin 1 of the PLL should not change when you key up. It is possible that there may be other components that have been cut. You never know whose hand was in the radio before you got it.
If your voltage output on pin 1 of the PLL is not steady then the feedback loop frequency .790 MHz is not strong enough or is unstable. If your radio is transmitting then the radio cannot be Out-Of-Lock so the .790 MHz should be there.
If you have a working microprocessor chip for the counter then go ahead and replace it. If the display is 92.2000 MHz then chances are the IC is N/G. Having a working counter for the Cobra 2000 GTL will go a long way into helping you fix the radio.
As for replacing the MB-8734 with an MB-8719, the pin-out is the same, just go ahead and swap them out. Notice that the PLL is upside down from the board markings. Make sure you put the new PLL in the same way. Never ground pin 10 of the MB-8734 or it will pop the chip. On the MB-8719 pin 10 is the divide by "N" Pin. You will notice that this pin is grounded on the Cobra 142 GTL and uses an 11.1125 MHz loop crystal. On the Cobra 2000 GTL pin 10 is not grounded and uses an 11.3250 MHz loop crystal. On the Cobra 148 GTL an MB-8719 PLL is used but the loop crystal is an 11.3258 MHz. By using an 11.3258 MHz crystal will allow L-59 to be adjusted with it in the middle of the coil and you won't have to bottom it out to get close to the operating frequency.
This is how they get channels on the Cobra 2000. They ground pins 10 and 11 in different configurations to get the extra channels. It is much easier to align the radio with the voice-lock unlocked. Make sure that the voice-lock is completely factory or completely opened. It is possible that when the radio was set back to factory that not all of the components were put back in place.
Good Luck
If D-75 and D-52 were cut then the radio's voice-lock was opened. Resolder D-75; it in is series with D-52. D-52 is cut when the voice lock is unlocked. Adjusting VR-5 will set the Tx frequency. If the voice-lock was unlocked then VR-5 is disabled. It sounds like someone had the voice-lock unlocked, and then put it back to factory.
With the voice-lock opened (Unlocked) the clarifier (Voice-Lock) will cause both Tx and Rx to deviate from frequency and track together. If your Voice-Lock is factory and locked that would explain why Tx and Rx will not track. With the voice-lock opened the voltage on Pin 1 of the PLL should not change when you key up. It is possible that there may be other components that have been cut. You never know whose hand was in the radio before you got it.
If your voltage output on pin 1 of the PLL is not steady then the feedback loop frequency .790 MHz is not strong enough or is unstable. If your radio is transmitting then the radio cannot be Out-Of-Lock so the .790 MHz should be there.
If you have a working microprocessor chip for the counter then go ahead and replace it. If the display is 92.2000 MHz then chances are the IC is N/G. Having a working counter for the Cobra 2000 GTL will go a long way into helping you fix the radio.
As for replacing the MB-8734 with an MB-8719, the pin-out is the same, just go ahead and swap them out. Notice that the PLL is upside down from the board markings. Make sure you put the new PLL in the same way. Never ground pin 10 of the MB-8734 or it will pop the chip. On the MB-8719 pin 10 is the divide by "N" Pin. You will notice that this pin is grounded on the Cobra 142 GTL and uses an 11.1125 MHz loop crystal. On the Cobra 2000 GTL pin 10 is not grounded and uses an 11.3250 MHz loop crystal. On the Cobra 148 GTL an MB-8719 PLL is used but the loop crystal is an 11.3258 MHz. By using an 11.3258 MHz crystal will allow L-59 to be adjusted with it in the middle of the coil and you won't have to bottom it out to get close to the operating frequency.
This is how they get channels on the Cobra 2000. They ground pins 10 and 11 in different configurations to get the extra channels. It is much easier to align the radio with the voice-lock unlocked. Make sure that the voice-lock is completely factory or completely opened. It is possible that when the radio was set back to factory that not all of the components were put back in place.
Good Luck
Respectfully as always,
Rick
Rick
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redlght
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Still working on it so far i have replaced some caps. fixed the dis connected pin 9 of the pll back to the board, had to change the x3 xtal 10.240 it was reading low and not allowing me to tune some of the tp's. Having a rough time getting tx and rx to line up, have not unlock the clairifer yet. Have not swapped out the pll for the 8719 yet either. btw counter i am using is a victor VC3165 the scope i am using is a Philips pm 3055. Ill post some tp numbers soon. If i don't go insane by then lol.
Tuesday, 16 April 2013, 13:54 PM
Also have swapped out the old xtal for the 11.3258 MHz one.
Wednesday, 17 April 2013, 11:24 AM
OK here are the numbers after the = sign is the result i got wth is up with this junk: FC= Freq counter OS= oscilloscope
FC to tp13/ch19 check 10.240= 10.2421
OC to tp10/ch19am check for max = max
Meter to tp9/ch40am adj 3.00v check for aprx 2 ch1 = ch40 3.0v ch1 2.02
OC to tp1 adjt max = max
FC to tp1/ch1 AM ck 34.7650 = 34.7655 lowest possible slug to top of can
FC to tp1/ch1 USB ck 34.7665 = 34.7671 lowest possible slug to top of can
FC to tp1/ch1 LSB ck 34.7635 = 34.7636 slug to top of can if i go any lower receive drops out no static out of speaker
FC to tp10/ch1 AM ck 0.790 = 0.79028
FC to tp3/ch19 USB ck 7.8015 = 7.80013
best can get out of ct2
FC to tp3/ch19 LSB ck 7.7985 = 7.79766 best can get slug bottomed out
FC to tp14/ch1 AM XMT ck 7.800 = 7.8001
FC to tp15/ch19 AM ck 7.3450 = 7.34503
FC to ANT./ch1 AM XMT ck 26.9650 = 26.96500
Wednesday, 17 April 2013, 11:37 AM
Is it possible doing the 11.3250 MHz loop crystal with an 11.3258 MHz swap and not putting in the mb8719 with it giving me problems? Also Xtal 10.240 was showing 10.238 i swapped it out now it reads 10.2421 all this was done before the above tests and adjustments.
Thursday, 18 April 2013, 10:49 AM
Only part of this radio that seems to even be close is am
Saturday, 20 April 2013, 9:52 AM
Swapped back to the big can 11.32578 xtal got it lined up really close but got bad audio hum out going not incoming.
Sunday, 21 April 2013, 21:40 PM
Tracked the audio hum into the pa amp circuit. lifted C110 the hum was gone.
Sunday, 21 April 2013, 21:46 PM
It all fell into place when I placed a wire to L22 and the 11.325 xtal back on and poof the alignment went good. Last owner must of lifted it for some reason.
Friday, 26 April 2013, 6:19 AM
Latest installment of the cobra 2000 saga....It is lined up now
but on tx i get 27.40500 on ch40 down to ch1 but ch 9 down to ch 1 is off example ch 1 is 26.96499 and tx is rock solid just off from ch9 to 1
also receive drifts some times to the point of having to turn fine and course all the to one side or another.
IC4 shows 8.01-2 volts jumps back and forth on receive but 8.01 solid on tx And the radio is warmed up fully any clues?.
I did not recap it yet think that might be my issue? also any good tips when you do tune the coils as to how to move them ever so slightly lol damn buggers are tough to get dead point on the numbers like re wax the slugs or something?
Thanks in advanced.
Friday, 03 May 2013, 6:50 AM
Admin you can go ahead and 86 this thread save some room, it died.
Tuesday, 16 April 2013, 13:54 PM
Also have swapped out the old xtal for the 11.3258 MHz one.
Wednesday, 17 April 2013, 11:24 AM
OK here are the numbers after the = sign is the result i got wth is up with this junk: FC= Freq counter OS= oscilloscope
FC to tp13/ch19 check 10.240= 10.2421
OC to tp10/ch19am check for max = max
Meter to tp9/ch40am adj 3.00v check for aprx 2 ch1 = ch40 3.0v ch1 2.02
OC to tp1 adjt max = max
FC to tp1/ch1 AM ck 34.7650 = 34.7655 lowest possible slug to top of can
FC to tp1/ch1 USB ck 34.7665 = 34.7671 lowest possible slug to top of can
FC to tp1/ch1 LSB ck 34.7635 = 34.7636 slug to top of can if i go any lower receive drops out no static out of speaker
FC to tp10/ch1 AM ck 0.790 = 0.79028
FC to tp3/ch19 USB ck 7.8015 = 7.80013
best can get out of ct2
FC to tp3/ch19 LSB ck 7.7985 = 7.79766 best can get slug bottomed out
FC to tp14/ch1 AM XMT ck 7.800 = 7.8001
FC to tp15/ch19 AM ck 7.3450 = 7.34503
FC to ANT./ch1 AM XMT ck 26.9650 = 26.96500
Wednesday, 17 April 2013, 11:37 AM
Is it possible doing the 11.3250 MHz loop crystal with an 11.3258 MHz swap and not putting in the mb8719 with it giving me problems? Also Xtal 10.240 was showing 10.238 i swapped it out now it reads 10.2421 all this was done before the above tests and adjustments.
Thursday, 18 April 2013, 10:49 AM
Only part of this radio that seems to even be close is am
Saturday, 20 April 2013, 9:52 AM
Swapped back to the big can 11.32578 xtal got it lined up really close but got bad audio hum out going not incoming.
Sunday, 21 April 2013, 21:40 PM
Tracked the audio hum into the pa amp circuit. lifted C110 the hum was gone.
Sunday, 21 April 2013, 21:46 PM
It all fell into place when I placed a wire to L22 and the 11.325 xtal back on and poof the alignment went good. Last owner must of lifted it for some reason.
Friday, 26 April 2013, 6:19 AM
Latest installment of the cobra 2000 saga....It is lined up now
but on tx i get 27.40500 on ch40 down to ch1 but ch 9 down to ch 1 is off example ch 1 is 26.96499 and tx is rock solid just off from ch9 to 1
also receive drifts some times to the point of having to turn fine and course all the to one side or another.
IC4 shows 8.01-2 volts jumps back and forth on receive but 8.01 solid on tx And the radio is warmed up fully any clues?.
I did not recap it yet think that might be my issue? also any good tips when you do tune the coils as to how to move them ever so slightly lol damn buggers are tough to get dead point on the numbers like re wax the slugs or something?
Thanks in advanced.
Friday, 03 May 2013, 6:50 AM
Admin you can go ahead and 86 this thread save some room, it died.
