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I have a Cobra 29LTD serial number 43011339 that has no TX or RX. The radio powers up but the RX led is not on. TR 23, R105 and TR 21 get hot to the touch as soon as the radio is powered up. I replaced these three components and they still get hot when the radio gets powered up.
Re: I have a Cobra 29LTD serial number 43011339 that has...
Hi,my name is John. you need to adjust both TR23 & TR21 to 8 volts.......then you should be OK.......good luck. Rate this solution on the four thumbs--up.thanks John.
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if a mod has been done to the cobra 29 (all 29,s)the light will come on just find vr6 audio the radio as it comes on adjust vr6 untill it goes away,,,,always trust your watt meter(s.w.r scale)over the flashing light its really easy to do it beats paying a shop $10-$15
all functions of the radio are performed by the main IC 2816c . The frequency is controlled by this also and if it is blown you will loose your frequency and the problem that emits is in your statement.
1 why would you change the finals?? Have you checked you antenna? How are your SWR's? Crappy antenna's cause a lot of problems.
Use an external meter to see what the SWR is, and see what the output is PEP. If its low, then there is something wrong. If it is High, change the mic and turn up the dynamic all the way.
Next. Have you been messing around in there?? Tryin to get more wattage? You turned VR4? If you thought you were turning it up by turning it all the way to the right, you turned it all the way down. Turn it all the way to the left.
D23 is the reverse protection diode and it shorting is the primary
reason your fuse blew. As you posted, power was applied in reverse,
hence other components would also fail. Pls check:
1. D22 - 9.1V Zener Diode
2. TR23 (2SC1096) 9 Volts regulator
3. D19 - 5.1 Zener Diode
4. IC4 (TA7222) - Audio Amp
5. TR14 (2SC2029B/10) - Finals
6. TR15 (2SC2028B/20) - Driver 7. Most capacitors over 220uF (like C123, C114 & C112)
Hope that this be of help/idea. Pls post back how things turned up or should you need additional information.
i am having this trouble as well. The ics was my thought too, but I think it is in the modulation circuit somewhere. another article i read said to check this.
"Look for the collector of TR-23, you should read about 4.5 V with a dead key. If you find that this voltage is not present, check on the opposite side of R-120 for 6.5V. Most likely this voltage will not be present; if this is the case, C18 has shorted and needs to be replaced. This is a 330uf, 10V electrolytic capacitor beside L31. To prevent "future" problems, replace with a 16V unit."
As of yet, i havent gotten that far. note this is from the cobra 2000, but they are very much alike. you might cross check the resistor capacitor numbers though.
btw, isnt the mb3756 the pll ic?
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