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Cobra 142 no output power or receive

Chipper

Chipper

Active Member
Dec 18, 2018
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Hello I have a 142 that has no tax power output but keys up a radio beside it dummy loan to antenna and can see little rf on the scope threw the rf chain cans. On the receive end I got a snow sound and pick up a local here but he’s close and very loud on other radios but here’s the odd thing all functions of this radio works lights controls switches and all except squelch it changes nothing. The radio has not had any mods done to it still the same glass bulb meter lights even. What I did first was recap radio like I always do to these old cobras and nothing changed so pulled driver and final checked on transistor checker and they are good so now what lol ssb also does not work tx or rx plugged external speaker in pa and have audio in both modes. I can lock and unlock VFO voltage can so that works any suggestions will help me get this back up and running for a local that’s down hoping to get back on air thanks again for your help I’ve loaned him a 148 til I get this working again I’m just really learning to help out this hobby in my area there is no one here that works on radios anymore so a little help will is greatly appreciated thanks
 

Also changed out vco block new and am regulator nte 152. Removed old glue and crystals no corroded legs there I’m lost on this one
 
Not to put too fine a point on it, but have you attempted any alignment? Do you have any history on this radio, like maybe the last time someone saw it work?

Or, they saw it work until someone tried to fix it? A little history can remove a load of uncertainties.

It must be generating a transmit signal at the lowest level if you can hear a weak signal from it in a monitor radio on the same channel.

The peaks on some of the transmit adjustments are abrupt enough to totally shut down any wattmeter reading with just one out-of-tune slug.

Watching the S-meter on the monitor receiver will allow you to see if L26, L27 L28 and L29 show a proper peak. If any of them fail to do this, that points to a problem in that coil, or the circuit that feeds into it.

The receiver trouble may have a similar cause, but there are more tuning slugs to consider than the four in the transmitter's low-level circuits.

73
 
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The history of it he said it’s not had then top off til I got it and the gentleman said it’s always worked for him he had let it set a few yrs after taking a break from the hobby then when he turned it on one day it was quite and it’s just been sitting on the table in his living room til I told him I’d try to fix it for him. What’s the alignment procedure for this radio I can’t find anything for it thanks again. I’ve got it hearing great with a preamp hooked to it so I put 2sc2999 transistor in it and that helped people are low but I can hear them now without preamp. But could the squelch be on and I don’t know it
 
Also is there a place to find voltage checks for the regulator i have believe it’s pin 5 at 8 volt going to zero on tx and I think pin 3 13 volt pin 8 has I believe 8 volt. I do have pin 9 of the 8719 at 8 volts might need those pins volt checks as well. And where can I purchase the tuning cans if I have one that’s bad, does the (LA-***) have to be the exact matching number or is there a tolerance for these
 
Chipper said:
Do u have the procedure for this radio thanks
Click to expand...
I'm assuming you can read schematics, the 2000 is so close albeit different reference designations that you can use the 2000 service manual to get aligned.
 

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711 said:
I'm assuming you can read schematics, the 2000 is so close albeit different reference designations that you can use the 2000 service manual to get aligned.
Click to expand...
Thank you for this I’m able to read them for the most part I’ll see how this goes tonight after work thanks
 
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Tea berry stalker seems to be the same board as 142 so I did alignment couldn’t get any tx alignment til I put my scope on the combiner then adjusted tx coils for max on scope but still nothing on watt meter but more signal on my other radios meter now but still no audio in am and very weak audio on ssb. This radio has a lot of the 945 transistors in schematics but there are 711 in mine where the 945 should be and 180* from the board outline. Squelch still don’t work either. I have a parts 142 board here that is all intact but lots of corrosion on it but makes for good reference. Is there any suggestions now on what to do from this point on. Thank y’all
 
I put a new 11.325 in now on ch 19 am at tp1 on the counter I get 35.620 MHz and it should be 34.9850mhz can I get some help on what’s off now I’m bout to go crazy lol
 
It's exactly 64 channels too high.

Suggests that pin 10 of the 8719 is grounded.

Isolating that pin from ground should then get you channel 19, rather than 27.825 that you're getting.

That pin gets grounded for the factory-original 11.1125 MHz crystal. Using the 11.325 simplifies adding channels above 40, but you have to isolate pin 10 from ground to make the arithmetic come out right for channels 1-40 with that crystal. A switch to ground that pin will move you upstairs 64 channels across the board from channel 1 (27.605) to 40 in the display, 28.045.

73
 
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Ok thanks for that info I just put the old crystal back in it in case I was going to mess it up. I still can’t get it to transmit anything I do have receive now however it’s not 100 % yet but it’s more than I started with. I’ve changed out the so42 chip driver and final am regulator voltage regulator pre-driver and 2 tuning cans all new parts from rf parts that I’ve had for a year or so and pulled my spare board from a 142 out and used it for reference and recapped the whole right side of the board again from mic amp to am regulator pulled all crystals again to make sure no glue was around them I’m finding nothing on this thing. I scope a signal from the can in front of the vco block all the way to the driver driver then it steps down low then put probe on final it lower the antenna jack and it’s a fine line on the screen I just don’t get it. Thanks for your help on that crystal I really need schooled on this radio that would be helpful
 
Only two frequencies get mixed together to produce the transmit signal.

Do you have another radio you can put on the same channel to listen for a weak signal? A coax jumper on the monitor radio will get you a half-inch long 'sniffing' antenna at the other end. If you can't hear a carrier when the 142 is keyed this way, you're missing either one or the other of the two signals feeding into the S042 mixer chip. If they both reach that chip at all, you'll hear it sniffing from a few inches away.

73
 

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