Realistic TRC-465 Issues

[wcsd106]

Hello,

I recently picked up a Realistic TRC-465 radio. I bought this radio with issues, but from the description, it sounded like an audio IC.

Issues:

• Receive but no audio output
• Transmit but no Modulation
• No PA Function
• Radio is getting hot near Audio IC / L7808 8v Regulator

I replaced the audio IC with a new one I had in my parts inventory, but that did not solve the problem. The heat issue is still there, and obviously someone has messed with this radio before as "HOT" has been written in permanant marker near that section of the radio.

After more investigation, I found that the 8v regulator is the component getting hot in that area. I pulled the 8v regulator to replace it, and found that it had gotten hot enough to melt through the thin plastic insulating film.

I am currently out of 8v regulators, and have no local outlet to purchase them. I have some on order, but it will be a few days before I get them. In the meantime, I tried injecting +8v to the spot on the board where it belongs. I am still not getting audio or modulation and the PA function still will not work.

I have wired a microphone standard realistic 5 pin Din... Most websites I've seen do not have a listing for the microphone wiring for a TRC-465, and I no longer have the books that I used to have when I used to work on radios for a living.

Can anyone confirm that the Realistic TRC-465 microphone is wired standard:

1. Shield / Common
2. No Connection
3. TX
4. Audio
5. RX

If that is the correct wiring for this radio, then I will know for sure that the microphone is wired correctly.

If anyone can offer some advice, it would be greatly appreciated. This radio only seems to have problems in the audio section as Transmit & receive are right on to specs.

 

[MisterFatty]

If you have a schematic start checking capacitors on the 8 volt line, sounds like one has gone bad.

If you have no schematic you could isolate the 8 volt line a section at a time and find out where the high current drain is, once you find the section which is bad narrowing it down from there should be easy.

 

[wcsd106]

Thanks for the reply... I'm fortunate enough to have both the schematic and the service manual on this radio... been studying over it for the past hour or so.

 

[TonyV225]

I was also going to say check the 2 caps in the right back corner of the board they are I believe 25V 1000uf

 

[wcsd106]

I really need to get a PC out in my repair room lol... I just came in from another hour or so of troubleshooting this radio. One of the 25v1000uF caps looked bad, top slightly bulged, so I replaced it.. I'm still in the process of isolating 8v sections of the radio, but so far have not been able to come up with anything. The 8v regulator is getting hot within the first 10-15 seconds of turning on, so I'm giving it a rest to keep it from completely blowing until I get some replacements in.

 

[TonyV225]

Good idea and your a wise man. Theres no sense of making more problems

 

[loosecannon]

first make sure that regulator is not making electrical contact with the chassis due to the melted insulator.

you might try checking Q33 with the diode test function of your DMM.
you have to remove it from the chassis before you test it.

also try checking C118 and C119 by removing them from the chassis and checking them for shorts.

are the voltages on the audio amplifier chip correct?

LC

 

[MisterFatty]

I probably should not have assumed you checked the 7808 first, if you isolate it in sections you start from it, and move away from it. Doing it this way will first check the install of the 7808, and verify what LC was mentioning. If you did not already do this you need to.

Isolate the 7808 from the rest of the circuit confirm normal operation, including temperature, once done you can move on if need be. Look at the schematic, find a convenient location to isolate a section somewhere down line, might be as simple as lifting an end of a resistor. Check that section for normal operation, and move on if need be. Doing it this way you should have already taken care of the issue causing the 7808 to pop.

There are better ways to do this but this one will get it done, even if you had no schematic.

Bulging caps, and the age of the radio combined with your symptom is a sure sign you should consider recapping the radio entirely. That is if your serious about keeping it running.

 

[TonyV225]

AS MENTIONED ITS UP TO YOU TO DECIDE WHAT THAT RADIOS WORTH AND HOW FAR YOU WANT TO GO WITH FIXING IT. I CAN WARN YOU NOW THAT YOU WILL SEE LED'S GOING OUT IN THE CHANNEL DISPLAY IF THEY HAVENT ALREADY STARTED. THIS RADIO AND ITS TWIN THE UNIDEN PC-122 ARE EXACT RADIOS WITH DIFFERENT NAME AND FACE PLATE AND THEY BOTH HAVE THE LED PROBLEM.

 

[wcsd106]

Update.

I have been able to get the receive audio back into this radio. Turns out the bad 8v regulator must have popped the new audio IC I put in. After hours of searching and testing, I came to the conclusion that the new audio IC had to be bad... replaced it and all is well.

I now have receive audio and it seems to be working correctly. However, I have another problem: I do not have any transmit audio.

Since the easiest way I can see to troubleshoot the microphone audio section is to start with the PA function, I have started there. I have tested the microphone element and it tests good. I have also used this microphone on another radio to double-check.

When I switch the radio over to PA mode, I get CB receive audio over the pa speaker. Keying the microphone mutes the audio, but there is no microphone audio heard over the pa speaker.

Checking my voltages on Q30 (the PA Amp) I have my 4.5v at the collector, as per the service manual, but the Base and Emitter voltages are both over 7v.. Per the service manual and schematic, the base voltage should be 2.5 and the emitter voltage should be 1.8v

I can't figure out where these higher voltages are coming from. The schematic for this radio can be found over at cbtricks.

Anyone feel like troubleshooting a problem radio again?

Thank You.

 

[Big Dummy 123]

this radio is thre same as a unden pc 122xl yhanks Ben

 

[wcsd106]

Sorry for not replying to this more quickly.. I ended up getting this radio back working. It had a bad case of the "10 volt blues" and there were several electrolytic caps that were either shorted or blown.

It's working like it should now, and I finished getting a Galaxy N Kit put into it a few weeks ago. Once the weather breaks I'll get around to pulling my radios I have in the mobile and setting them up differently to allow for this one to be installed in place of the Cobra 18wxst2 I have in there at the moment.