Superstar 121: No FM TX Audio

[Judge]

Hi there. Bear with me, as I am quite new to all of this.

I've acquired a second-hand Superstar 121 radio, (PCB EPT120113Z). While AM TX audio works perfectly fine, FM TX audio is pretty much non-existant.

While using a spectrum analyzer, I adjusted the FM deviation (VR5) with no change. Using a nearby SDR receiver, with the volume and gain at its highest, the FM TX audio is extraordinarily faint.

Upon inspecting the radio, it's been "worked on." TR32 AMC limiter is gone, J4 clipped(?), R205, R206 clipped, orange wire soldered to PCB component side of D84 (going to RF gain?).

Wondering if someone can guide me into next steps/direction in troubleshooting the FM TX audio issue?

Thank you!

 

[Robb]

While this suggestion may not fix this radio, I would still recommend that you restore the chassis back to OEM. Then, you might begin to look for the problem.

 

[Judge]

Thank you. We're on the same page. I've already soldered back some of the clipped components. At least the ones I could find. I will need to replace the AMC transistor but I'm not sure if I have the part on hand.

I'd really like FM audio to work on this radio, and I definitely want it back to the factory configuration.

 

[sonoma]

the wire soldered to the top of d84 is more than likely a factory item. watch what you are doing or you will mess up the radio even farther. I have 2 of these radios myself and they have a wire soldered in the same location. most people pull the limiter on this radio to get more audio from it since they are low using the vr to adjust it. with the limiter in place you will get about 60 to 80% modulation.
with FM not working you may find a bad solder joint under the little metal cover on the solder side of the board or one at the audio IC. this is a common problem for this radio the past few years. you start soldering parts back in place could cause you more problems if you do not see what they actually did to the radio to that point. I am seeing so many new guy's soldering things back in place then blow up the radio. if it is working fine do not try to redo the mods back to stock since you may not get it right. I like the 121 radios at least the 1st versions since they did not have the bad solder joints as the newer ones. I do a npc mod to mine for swing and audio increase to make the radio wake up some. the mod is easy to do but not for the newby to do since if done wrong can kill the radio

 

[sp5it]

Check D31, D32, D30, D30-1, TR26, TR27, L17, L18
Mike

 

[sonoma]

here is a 10kc mod some due. you can look at this for switches and extra parts

Wanna add a +10 KHz jump to that radio? Here's the info. This works with radios with the EPT120112Z board...

On the component side of the board...

1) Unsolder J25 (jumper)

2) Solder a 4.7K 1/4 watt transistor in place of J25, and in then run a lead from leg of the newly installed transistor closest to J28 (the left) to one pole on a SPST toggle switch.

3) Solder another lead from the other pole on the SPST toggle to J27.
here is the extrs channel mods so you can look to see what it takes. also they may have a switch for talkback on and off.
Channel Expansion


1)You will need 3 SPST switches and mount them in the radio.
2)Find the PLL MC145106.
3)Locate pin # 10 and cut the trace going to this.
4)Switch #3 will be soldered to the cut traces on pin # 10.
4)Solder wires to the other 2 switches as in the picture above.
5)That's it! ALl the switches down will give the normal channels of the radio.
With the radio in 'HIGH' band and switch 1 UP , 2 DOWN , and 3 DOWN:

You get 27.845 - 27.955 on channels 10 to 19.

With the radio in 'MID' band and switch 1 UP , 2 UP , and 3 DOWN:

You get 27.925 - 28.065 on channels 1 to 12.

With the radio in 'HIGH' band and switch 1 UP , 2 UP , and 3 DOWN:

You get 28.045 - 28.155 on channels 27 to 38.

With the radio in 'HIGH' band and switch 1 DOWN , 2 DOWN , and 3 UP:

You get 26.135 - 26.575 on channels 1 to 40.

here is a link for extra mods that is drawn out. might help you more to see how its done with pictures.
http://kg4zpn.netai.net/cb/superstarmods.htm