Texas Ranger TR-127FST

[danmcclain]

I just received this radio from Ebay untested. When powered up there is no audio. It transmits fine. Nothing on PA either. Any ideas what the problem could be???? Thanks Dan

 

[jkp1]

I’m just wondering how you know it transmits fine if there’s no audio.

 

[Handy Andy]

I'd like to know too...

The thing uses a mod transformer, so to me it indicates work on Talkback issues, you have AM so that tells me one live side of the transformer works - no PA relates to the output winds of the mod transformer that connects to the other open lead pair side.

So check CB/PA switch - look for problems in and around the EXT SP and PA jacks.

Also check squelch function - if you don't hear a "thunk" from the radios speaker during power up (the bootstrap) it might mean the Audio TA7222P chip needs help - new caps are probably what it is calling for. Affects SQ function too.

ADDED IN:

The radio uses a RELAY from Pin 4 to offer switching for the SPEAKER ground.
Might want to check that...

Also - since you may not have Receive, but shows RX and TX switching - Pin 1 and Pin 2 of the MIC JACK may have been reversed.

Check Board ground to Pin 2 of the Jack, if it shows a Dead short, there is your problem.

Then what about Pin1? That is should be your Audio (Mic line)

Here's why...

Service manual shows EPT012910A but wired for typical Cobra Uniden 4-pin Handset style.

Pin 1 - GND
Pin 2 - MIC
Pin 3 - TX
Pin 4 - RX

But look at the plug side schematically shows...

Pin 1 - MIC
Pin 2 - GND
Pin 3 - TX
Pin 4 - RX

See the swap?

So, if no noise, reverse Pin 1 and 2 - Pin 2 might need to be Ground at the HANSET to match the wiring shown on schematic. to the RADIO Jack

Short Pin 2 to Pin 4 - get RX? Theres' your answer.

Now, I'm back to Dinner with the wife...​

 

[danmcclain]

I'd like to know too...

The thing uses a mod transformer, so to me it indicates work on Talkback issues, you have AM so that tells me one live side of the transformer works - no PA relates to the output winds of the mod transformer that connects to the other open lead pair side.

So check CB/PA switch - look for problems in and around the EXT SP and PA jacks.

Also check squelch function - if you don't hear a "thunk" from the radios speaker during power up (the bootstrap) it might mean the Audio TA7222P chip needs help - new caps are probably what it is calling for. Affects SQ function too.

ADDED IN:

The radio uses a RELAY from Pin 4 to offer switching for the SPEAKER ground.
Might want to check that...

Also - since you may not have Receive, but shows RX and TX switching - Pin 1 and Pin 2 of the MIC JACK may have been reversed.

Check Board ground to Pin 2 of the Jack, if it shows a Dead short, there is your problem.

Then what about Pin1? That is should be your Audio (Mic line)

Here's why...

Service manual shows EPT012910A but wired for typical Cobra Uniden 4-pin Handset style.

Pin 1 - GND
Pin 2 - MIC
Pin 3 - TX
Pin 4 - RX

But look at the plug side schematically shows...

Pin 1 - MIC
Pin 2 - GND
Pin 3 - TX
Pin 4 - RX

See the swap?

So, if no noise, reverse Pin 1 and 2 - Pin 2 might need to be Ground at the HANSET to match the wiring shown on schematic. to the RADIO Jack

Short Pin 2 to Pin 4 - get RX? Theres' your answer.

View attachment 57578
Now, I'm back to Dinner with the wife...​

Thanks for the info Handy Andy, was wondering why it came with a Cobra handheld mic.... Dan