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Cobra 2K issues...
- Thread starter Hawkeye351
- Start date
Keep trying and never give up. You have what you need. The experience will come. If I get some free time I will try to help. I'm far from an expert, but I do alright.
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Then look at the stages with your spec an. See what is making power and where it stops. I still think your driver and final are suspect. The collector voltages drop way down in TX. Just be mindful of the max input of the spec an. Use a power attenuator in front of the input if necessary.
I use a 50db sampler.
I know the bare basics. I've learned a lot by this site. Just some things I'm confused about, but it'll eventually hit me.
I'll replace both the driver and final, then try again. I did notice the logo on the driver does seem slightly different than the final.
I know the bare basics. I've learned a lot by this site. Just some things I'm confused about, but it'll eventually hit me.
I'll replace both the driver and final, then try again. I did notice the logo on the driver does seem slightly different than the final.
Regarding the static, if it's like sizzling bacon and popping, possibly intermittent, make certain the trace side of the board is squeaky clean after soldering. I chased my tail for days once for same issue and the flux left behind after soldering was to blame. I found out it was conductive enough to cause issues. I use 91% iso alcohol for new work and a 50/50 iso/acetone mix on a q-tip or toothbrush on the old gunk. Keep the iso/acetone off the component side as it may remove markings on transistors, diodes etc and will melt certain plastics (like meter face).
Well, I rechecked the pre-driver cause the collector voltage was higher than the service info states for AM mode. I noticed the base wasn't even soldered. I resoldered that leg, now I'm seeing 1/4w deadkey and no swing on AM. On sideband, I'm seeing 1/4w swing. Still no current draw on the driver bias adjustment, but final bias adjustment is still set to 70ma. Replaced C153 and C214 again. Looking on spectrum, I see a very strong signal on frequency, and can now pick up the signal on my monitor radio, but only 1/4w showing on watt meter. Fixing to replace driver and test again.
Can you send photos of the two devices that are (were) in the radio that came from eBay? BTW, I don't even try to use Mitsu, NEC, Toshi parts any longer. I change to MOSFET. The fakes are not worth the hassle and the HG parts suck.
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An easy way to tell fakes from real parts is to look at the surface finish. The fakes often have the face burned off with the same laser that etches the new fake number into them. Very few take the time to polish the face after removing the original markings. The laser will almost always make the face look matte compared to the rest of the surfaces. Cable Guys picture illustrates this well, look at the 1969 finish.
Did they ever swap fonts?
Have you tried to tune the output power circuit by the book?
Won't put out power if it's all out of wack ............
Won't put out power if it's all out of wack ............
Well, got the transmit working great again.
Replaced driver, 2166 (it was original, had tips between legs) with a 1306.
Reset bias for 30ma on driver.
Reset bias for 70ma on final.
Realigned output stage
AM - Deadkeys 2.5w, swings to 18w peak, swings up to 6w in average.
SSB - 25w peak
Sounds awesome on monitor radio on same frequency.
Now just gotta figure out why there is static coming through speaker with volume turned all the way down. When I turn volume up, I can then start hearing local stations but still has that static noise in it. When I turn volume down, then the receive volume drops down but that static noise stays in there.
Gonna clean up this flux from bottom of board (mainly in front of and around the 3756 and 7222 ICs.
Replaced driver, 2166 (it was original, had tips between legs) with a 1306.
Reset bias for 30ma on driver.
Reset bias for 70ma on final.
Realigned output stage
AM - Deadkeys 2.5w, swings to 18w peak, swings up to 6w in average.
SSB - 25w peak
Sounds awesome on monitor radio on same frequency.
Now just gotta figure out why there is static coming through speaker with volume turned all the way down. When I turn volume up, I can then start hearing local stations but still has that static noise in it. When I turn volume down, then the receive volume drops down but that static noise stays in there.
Gonna clean up this flux from bottom of board (mainly in front of and around the 3756 and 7222 ICs.
With and without mic. Just a constant level of static (white noise).
It may be this flux all over the trace side of the board. I just cleaned the audio IC and switching regulator section thoroughly, checked it out and the noise is almost non existent now. Gonna finish cleaning rest of the board and get back with y'all later on an update.
It may be this flux all over the trace side of the board. I just cleaned the audio IC and switching regulator section thoroughly, checked it out and the noise is almost non existent now. Gonna finish cleaning rest of the board and get back with y'all later on an update.
Update:
Used isopropyl alcohol and a toothbrush to clean the entire trace side of board of all that flux residue.
Radio works beautiful. Receives great, transmits great, all voltages on the money, all frequencies on the money, all controls/switches work as new, meters working as new.
Only thing extra I did was replace the power supply regulator (1135) and the passthrough regulator (1135) with 6487G's.
AM - Deadkeys 2.5w, swings to 15w peak (22w pep), swings forward to 6w in average.
SSB - 18w to 20w
Thanks guys/gals...
Lesson learned, that flux residue can conduct and cause issues, therefore always clean up any flux residue.
Used isopropyl alcohol and a toothbrush to clean the entire trace side of board of all that flux residue.
Radio works beautiful. Receives great, transmits great, all voltages on the money, all frequencies on the money, all controls/switches work as new, meters working as new.
Only thing extra I did was replace the power supply regulator (1135) and the passthrough regulator (1135) with 6487G's.
AM - Deadkeys 2.5w, swings to 15w peak (22w pep), swings forward to 6w in average.
SSB - 18w to 20w
Thanks guys/gals...
Lesson learned, that flux residue can conduct and cause issues, therefore always clean up any flux residue.
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