can anyone tell me what to check to see what to replace ..i have great RX no audio on c.b. or p.a. and the meter needle goes backwards instead of forward when keyed..thanks
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cobra 25 no audio on tx or p.a.
- Thread starter johnecashflo
- Start date
Hmmmm ? No audio / No P.A. , but receives , but the meter goes backwards ? Hmmmm Sounds like audio chip , but yet the needle goes backwards when you key ? Can you tell if your at least throwing a carrier out ? Do you have another radio you can put inline and key your bad radio and see if the other radios registers a receiving signal ? if so , that would pretty much mean your power final is OK , that being the case , audio chip would need changing. It's sometimes hard to tell by word of mouth John , but if I were a betting man , I'd say audio chip.
USUALLY... on a cobra if the audio chip is bad then it will not have receive audio.. One quick test is to check voltage on the first and last leg of the audio chip... Should be around 13.8 on both ends...
I would check mic and check for cold solder joints... Also might want to clean the mic gain knob..
Just a few thing to check out.
I would check mic and check for cold solder joints... Also might want to clean the mic gain knob..
Just a few thing to check out.
johnecashflo said:
your saying you have receive audio but yet you have no power out but yet your PA doesn't give you audio out either .......right ? Did this radio work before ? What happen when this radio decided to start all this weirdness for you ? I've seen them hooked up backwards and still fire up but they just wouldn't work ? I hear you when you say it receives but when you key the mic the needle goes backwards with no power out , I've dealt with a few blown audio chips in my time but the power was still there , changing the final is worth a try.
welll it aint the final or audio chip,driver all checked ok.. i broke down and took it to the local c.b. shop he seem to think it is the circiutboard that is mounted to the side of the radio .board is about the size of an echo board its marked (KEPC-264-B1..)he also seems to think the radio was shorted out, the reverse protector was changed thanks for all the help..
went to c.b. tricks found some info on the board its called a compander board..anyone know what it does and can that be my problem
did you check youe modulation transformer i have had one fry and caused an audio problem. mine was caused by someone soldering a jumper on D10 and caused the radio to self distruct. it blew out the audio chip and it wouldnt rx that well. just a thought. you can usaully tell because the transfromer will look like it got hot and the traces will look like they got hot also. also check D10 to see if it opened up. you said you had carrier power right about 4 watts or so depending if it has been upgraded or not.
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I have a cobra 25 gtl that's been laying around the shop here and I have the same problem with, you would think after fighting with that thing, I would eventually have figured it out, but, nothing, replaced the audio IC, done this done that, nothing, no audio at all, here's what it does:
1) Keys with needle swing - shows a 4-5 watt dead key - no audio on TX
2) receives - can see needle moving with incoming signals - no sound in
speaker
It's not the audio IC, and it's not C-87
If anybody ever figures it out, lemme know.
1) Keys with needle swing - shows a 4-5 watt dead key - no audio on TX
2) receives - can see needle moving with incoming signals - no sound in
speaker
It's not the audio IC, and it's not C-87
If anybody ever figures it out, lemme know.
maybe cold solder joint. try pressing on the board while trying it out. just dont use metal object of course. use a plastic toothbrush handle or something like that. i found a good quick way to check audio chip, is lick your finger and run across the pins quickly, if you hear noise audio chip is usually good. i would say bads solder joint tho. just pick a corner to start in and work in small areas of the board. pressing on it while trying to transmit. dont go long tho let the radio cool off. then try more.
good luck
good luck
Yes, that is likely your problem. That's a speech processor of some kind. "Compander" is a term that means "compressor/expander". It usually affects both transmit and receive. I would remove that board and put the radio back to stock and see if that does the trick.
First reaction is the mic. If the mic is wired wrong, you may be able to make it key, but get no tx or rx audio.
If that's not it, look at the block diagram here:
http://www.cbtricks.com/radios/cobra/25ltd/graphics/cobra_25ltd_block.pdf
Look at the bottom right, around the AF Power Amp. It would have to be something in that area.
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