Audio stopped working ?

[tripplenickel]

Realistic TRC-55
Everything normal, signal strength good, swr check works, mic operation for both (on the air) (modulation) work as normal when transmitting, just no volume, even pa works. What gives ?????

 

[JayMojave]

Hello Tripplenickle: Wow that's a oldie but goodie!

What do you mean no volume, no receive audio, or no transmit audio?

See: Realistic TRC-55 (21-151)

The Receive and Transmit audio circuits are different, so being able to transmit with good audio doesn't mean you will have good receive audio. And visa a versa.

If your not getting Receive audio, it may be a good call to plug in a external speaker, or unplug the external speaker now plugged in, move around the external speaker plug. See what happens. Make sure your in CB Mode and not PA Mode, I've done that a few times.....

Jay in the Mojave Desert... just down the road ah ways from the fillin station

 

[tripplenickel]

Hello Tripplenickle: Wow that's a oldie but goodie!

What do you mean no volume, no receive audio, or no transmit audio?

See: Realistic TRC-55 (21-151)

The Receive and Transmit audio circuits are different, so being able to transmit with good audio doesn't mean you will have good receive audio. And visa a versa.

If your not getting Receive audio, it may be a good call to plug in a external speaker, or unplug the external speaker now plugged in, move around the external speaker plug. See what happens. Make sure your in CB Mode and not PA Mode, I've done that a few times.....

Jay in the Mojave Desert... just down the road ah ways from the fillin station

Jay, thank's for the reply. You can key the mic, ON THE AIR/MODULATION lamps work as should,the meter shows good signal and modulation, the SWR check work fine with 1.2, and you cannot hear any AUDIOl either through ext spk or radio spkr. I plugged in ext spkr, pushed PA button, audio is fine. I thought it may be dirty channel selector or ext spkr plug in, took top off and sprayed both of them really good with contact cleaner which made it easier but no audio help. I'm not ver savy with the inside, but nothing looks like it was ever messed with. This has got to be something simple, just no sound. I even sprayed the ANT connector, no change. I wish someone would chime in who has ran across this type of problem in the past. Anyway, thank's Jay, 3's to you/yours and all of you have a Merry Christmas. Waiting to hear back, take care.
555

 

[LoyalServant]

Check the microphone...

You can try installing a jumper between pins 1 and 5 on the mic jack to see if that's it before
mucking around in the microphone.

I am assuming your not getting any audio on receive... but your not being very clear about it because your talking about the modulation lamp, etc.

Looking at the schematic.... your mod indicator is blinking and this uses the old school method of modulating the carrier... so if the mod indicator is working and so forth you absolutely have to be transmitting audio unless someone butchered the rf deck in a very bizarre manner.

This has a dead simple audio amplifier/speaker switching arrangement.
Have headphones? Plug those in.
If still no rx you have:
- Bad/dirty headphone jack
- Bad/dirty ext speaker connector
(both of these have switches in them)
- bad/dirty cb/pa switch.
- broken wire/track someplace in the radio.

(after eliminating mic as cause of issue of course)

 

[tripplenickel]

LOYALSERVANT: What I was trying to say is when the mic is keyed, there is a ONTHEAIR lamp that lights up. When you speak into the mic, there ia a MODULATION lamp directly under the ONTHEAIR lamp that flashes as you speak showing modulation as it should.
When you press the PA button, you have you audio sound out the speaker, likewise with an external speaker hooked up. I have not tried the headphone jack but will tomorrow,
555

 

[JayMojave]

Hello Tripplenickel: Yeah great advice from LS there. Good call checking the receive audio with the headsets.

One other thing that has bitten me a few times, is the Squelch Control being turned up or is fully clock wise turning off the received audio. Verify the Squelch Control is fully counter clock wise. Some how we out smart our selves at times......

Jay in the Mojave

 

[Dawn]

I just looked at the schematic. As far as audio pathways are concerned, if the modulation light blinks to your speach and you can hear it in another radio to confirm it, that clears the differential pair and the tx secondary. If the PA works, that clears the Speaker secondary of the audio output transformer. You say the meter shows activity for receive. So we have the front end through the AGC cleared, leaving the detector and squelch left.

These are old radios and I'd hedge a bet on something simple like oxidized audio and jack contacts or the PA/CB switch. Perhaps wiring from the board to the connectors to check as well. Radio shack sells deoxit in tiny spray cans that just a drop, not a spray is needed short of burnishing the leaf contacts which you probably don't have a burnishing tool and not easily found.

If you had a cheap little signal tracer or even a computer speaker with built in amplifier and line input, you could make a probe and find where the audio is lost.
If the contacts show continuity with a ohm meter you should be good. That would then lead to a blocked squelch or for some reason the squelch circuit muting the audio or perhaps the detector or audio drive circuitry up to the differential pair that we know works.

 

[tripplenickel]

UPDATE////// I have sprayed jack connections including PA/EXT SPKR/HEADPHONE JACK on front panel, as well as SQUELCH through the outer shaft. I used a jumper wire to connect pin 1 to pin 5, no receive noticed from any of above done. All I get now with the squelch turned alway counterclockwise, is a small sound like a little motorboat, squelch knob will eliminate the sound when turned clockwise, which to me tells me the squelch control is working. I just don't know.
555

 

[LoyalServant]

It's doubtful you got any contact cleaner in via the shaft. You have to hit that from behind.
If your turning it and it's working the worst case here is a raspy control... gotta get it working first
then worry about noisy pots.

It sounds like you have something going wrong in the detector or the front end of the audio amp.
Does the position of the automatic noise limiter effect any change in it?

 

[tripplenickel]

If your talking about the 3 position fine tuning, nothing changes when moving any switched. The little motorboat sound will change when moving the squelch knob. After cleaning the the headphone jack by spraying and working the plug in/out several times, the noise id more consistent. With coax connected, there is no audio as it should be. That's about as far as I can go with my knowledge. Hope this helps. Thank's so much for sticking with me, I guess it's something out of my area.
555

 

[LoyalServant]

Schematic shows an "ANL" switch. I am talking about that.

Does this motorboat sound change pitch when you turn the squelch or just go away?
Does it change pitch when you move the volume control?

 

[tripplenickel]

Yes to borh questions, and it has a different sound when you push PA button.

 

[LoyalServant]

My first bet would be caps.... it's of that vintage that they have dried up, leaked, or both.
If your getting this motorboat in PA mode then we are back to an audio amp problem.

Just so I am getting it.... we have a radio with a motorboat type sound in pa mode and in RX.
There is no actual receive.. just the motorboat noise but it transmits with audio?

Can you confirm this motorboat noise is not in the transmit audio?

This is probably beyond what we can effectively troubleshoot on a forum.. just trying to isolate it to a particular area.

 

[tripplenickel]

The noise goes away when the mic is keyed.

 

[LoyalServant]

It would go away because the receiver is muted and speaker disconnected.

But.. can this noise be heard on another radio?

 

[tripplenickel]

No, I have my base set up really close and no noise @ all. The clock does not work, could this in anyway cause this problem ?

 

[LoyalServant]

No, more than likely the clock is just stuck or the motor has burned out.

If the TX audio is okay then the issue lies somewhere at the end of the detector and the audio buffers just in front of the audio amplifier I would wager.

If you tank on your other radio on the same channel does the S meter on this one move indicating it's receiving anything?

If I was working on this I would change all of the electrolytic caps C31, C33, C35, C39, C55, C59, C60, C61, and C64 just to start out then probe the issue down if that doesn't sort it.
If it resolves obviously move on to the other electrolytics in the radio and it will probably last another 30 years if good caps were used.

 

[tripplenickel]

Thank's for sticking with me on this, it's just too DEEPLY INVOLVED for me. I just thought it was something simpl but it is more than I am capable of doing. If I get a change to hook it up with my base station, I'll let you know if it receives a signal.
555

 

[JayMojave]

Hello Tripplenickel: That radio fix may not a real expensive fix from some repair shop, especially if you explain all the audio problems and trouble shooting you have done. As it appears to be a internal circuit failure. I would bet its a quick and cheap fix. Good luck.

Jay in the Great Mojave Desert..... the real estate lady said that the International Airport would be coming in, and that water would get cheaper, all that really happened was the property taxes got higher and my CB Antenna blew down.....

 

[LoyalServant]

Thank's for sticking with me on this, it's just too DEEPLY INVOLVED for me. I just thought it was something simpl but it is more than I am capable of doing. If I get a change to hook it up with my base station, I'll let you know if it receives a signal.
555

Not a problem.

Gives us old engineers something to do