Radio was plugged in backwards , with 3 amp fuse inline . I replaced d23 , and fuse ,brought it back to life .I tried several ( known good ) mics .Still no rx / tx .
Altho the rx / tx light does switch back and forth showing rx / tx
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Re: cobra 29ltd classic : no rx / tx
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.
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Make certain they are fully charged. I suspect the batteries. If the radio was left in the "on" position, it is very likely the batteries will not take a charge. The batteries can die in the drawer as well. Lithium batteries for all their good points really do not store well. (Yes, expensive lithium batteries such as your power tools or laptops do store well.) So, plan on new batteries. Many radios have become less expensive this year, so price out a new pair. That way you would have fresh batteries and a new charger.
Rx is an abbreviation for receive. (Tx is transmit) There are a variety of reasons a radio will be "stuck" in Rx:
1) Another radio in the group is stuck in transmit and you cannot reply if your radio is receiving the other radios transmission.
2) Your radio is programmed for Rx only.
3) Your radio has a Tx problem such as a bad mic, or something covering the mic opening.
4) Your battery is low or bad. It takes more energy to Tx than to Rx.
1- Did you choose the right Tone for both RX & TX?
If you have RF present but not the right tone, the green led should turn on. One of the side key should be a Momentary "Squelch Off" (By default, it programs like that). Use it when you you see the green led turn on.
If you have the wrong Tone Squelch programmed, the side key will let you hear the repeater to confirm the problem.
2- If it didnt do the trick, Look for a RX/TX frequency mismatch. maybe your RX/TX frequencies are wrong for this channel?
3- If you have checked all the above, maybe your radio have a bad ceramic filter and your unit has lost it's sensibility. (Youll hear only people near to you.) If it's the case, usualy only one half of the filter goes bad. Try swapping the Bandwith type in programmation. If WIDE, try NARROW or the opposite. If you receive in narrow but not in wide, the filter is bad. In more than 50 radios with Sensitivity problem, I only got one with both Wide/Narrow sides of filter bad. If you have access to a spectrum analyser, on a "RX Test" you should see ~0.2uV. Anything higher than 0.3uV mean you have a serious RX problem.
Most Cobra / Unidens are easy by clipping D9. On this one D9 and L19. Just turn up L19 to top. Clip D9 diode. spread coils 1/16" inch. Also use 100uf capacitor (-) toward final across JUMPER staple near Final Transistor in back. Use meter(adjust to best swing) spread back coils,remove L10,L20 slugs or adjust them to top. The only radio that clips different than D9 is Cobra 29Ltd (D11) or Uniden pro510xl(D14).
G'day, I think your problem with the Cobra cb is in the microphone, you should have a plug on the Mic cord end ,try disconnecting this from the CB unit and see if it clears it self. If this does the trick your problem is in the Mic it self, or the cord has a fault in it. However if you still have a problem it may be that the transmitt/ receive relay located in the Cb is stuck on transmitt, sometimes this can be cleared by tapping the case with the handle of a screw driver, place towel on the case first to stop any damage to the case( this doe's not always work) you may in this case need to have it serviced all the best hope I have been of help, John
Check around the pcboard where the dc goes to the board, sometimes the foil will burn. Also chec the transformer, Chec that one of the wires did not come off the plug in the back. When you replaced the protection diode did it blow again? If not keep checking for opens on the pc board. When you said it was dead do you mean no lights at all or no tx and rx?