SOLVED!! Old radio repair, cant find any obvious fault.

Thread Starter

smyth602

Joined Jan 8, 2017
50
I wouldn't be surprised. I suspect something like that. Perhaps not by the present owner, the TS.

With the above tests we can check out the audio section and maybe more.
I can 100% confirm that I haven't touched any of them. If the radio had been opened before I bought it, it was well hidden as I had to slit the label down one side to open the case.

Is there a need to split the audio from the source into two channels like your cable does or will a stereo cable suffice? I have a splitter but it would require some digging to find.
 

MrChips

Joined Oct 2, 2009
30,720
We don't need stereo channels. One channel will do.
We still need access to either channel so if your source and amp are stereo (which is most likely) we need the splitter or a spare stereo cable that we can hack and destroy.

I posted the wrong photo the first time.
I have changed the photo to show 3.5mm stereo plug split into separate RCA jack.
You don't need the exact cable, only some way to get at a mono channel.
 

Thread Starter

smyth602

Joined Jan 8, 2017
50
ask and ye shall receive. one powered speaker with both high and low gain inputs, and a stereo cable that we can hack to pieces.

IMG_20170109_193939.jpg
 

MrChips

Joined Oct 2, 2009
30,720
Ah, good!

Now we need some musak source and similar connection.

If your AM/FM radio had been functional we would have had both pieces,
and of course we wouldn't need any of this. :rolleyes::p:)
 

Thread Starter

smyth602

Joined Jan 8, 2017
50
can i assume we might be cutting the cable in two, soldering one end to the board somewhere and the other end in place of the speaker?
 

Thread Starter

smyth602

Joined Jan 8, 2017
50
Is there a 3.5mm stereo jack on that thing?
Can you use that stereo cable and get sound out of your boom box?
Indeed there is. Listening to 2002's finest as we speak. Using a different cable now though as the first one was flaky if you wiggled it.
 

MrChips

Joined Oct 2, 2009
30,720
Indeed there is. Listening to 2002's finest as we speak. Using a different cable now though as the first one was flaky if you wiggled it.
So the cable deserves to be hacked. If you have two bare 3.5mm stereo jacks those will do too.
So if you're willing to destroy the cable, cut it into two equal lengths.
Remove about one or two inches of the outer plastic and get at the inner cables.
The LEFT and RIGHT should be colour coded and there should be a protective shield. We need to get at the signal wire and the shield as GROUND.
It doesn't matter which channel we use on either end. Mix if you wish. As long as we get two working, a source output and an amp input.
On the amp end, you may in fact join the two channels so that we convert stereo to mono.
 

MrChips

Joined Oct 2, 2009
30,720
Nice. Almost done.
Now you have to remove about ¼" of the plastic insulation on the red or white wire. It doesn't matter much which you choose (except if you say the cable is already flaky, you want to use the good channel).

Get the soldering iron out and tin the ¼" of bare signal wire and ¼" of the tip of the shield (GND).

Rejoin the bare wires and make sure it still works on the mp3 player and the amp.
 

MrChips

Joined Oct 2, 2009
30,720
You're a real trooper. We're all set to go.
One more thing, do you have any spare capacitors? Anything from 0.1μF to 10μF will do. Voltage rating doesn't matter for now.
If not, we'll manage without one.

Now we have two tests to perform.
1) To test the radio part of the circuit to see if it picks up a signal.
2) To test the audio part of the circuit to try to get some sound from its speaker.

We will tackle one at a time
 

MrChips

Joined Oct 2, 2009
30,720
(Save the 100μF cap for now.)

Ok, let's go.
We will see if we can get some audio from the radio.
You will used your boom box for this (that is what I am going call it from now on).

Connect the battery to the radio (I assume it is a 9V battery).

Solder the 3.5mm plug cable to the radio.
Bare wire is soldered to anywhere to GND, example shown.
Red wire is soldered to PIN 9.
Set volume control on radio to mid-way.
Plug 3.5mm plug to boom box.
Turn up the volume on boom box until you can hear something, even if it is hissing sound.
Adjust tuner on the radio and hunt for a radio station. (You will need to install the tuner knob and screw it on.)

Edit: I should have said, Set the radio to AM for now. If you cannot find a radio station try FM also.

AM_FM radio solder side audio out.jpg
 

Thread Starter

smyth602

Joined Jan 8, 2017
50
we have some success! on the highest gain the speaker can produce i am getting 2 different AM stations. nothing on FM
 

MrChips

Joined Oct 2, 2009
30,720
we have some success! on the highest gain the speaker can produce i am getting 2 different AM stations. nothing on FM
That's promising.
Is the volume control on the radio turned all the way up?
Can you describe the sound? Is it loud and clear?
Can you identify the two AM stations and their frequencies? (I presume they are UK stations).
(Will it be bedtime soon?)
 
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