Cure found for poor fm reception

[Lee1978]

Well, what a day, I finally have my fm back on my factory head unit.
Here's what happened. One day, out the blue, the fm on my pu-2473a head unit disappeared, it scanned and went through the motions of working but wouldn't pick anything up, on "am" on my stereo was working fine.
We thought it was most likely a problem with the rf board and my plan was to replace it with one from a donor radio, unfortunately one never came along.
More delving, testing and tracing through circuit diagrams later we finally came up with a fix that resurrected my old stereo.
Without explaining what was wrong or how this works I'll simply tell you what to do. Of course, this will only work if your head unit has failed in the same way mine did, I obviously can't guarantee this will work for you but if your radio's broken anyway, why not give it a try?

1. Take the stereo out of the car.
2. Take the stereo apart completely, right down to the main board which is soldered to the base plate of the stereo.
3. Remove the main board from the base plate, there are solder tags and a twist tag to undo, you'll figure it out.
4. Now, that silver box is the rf board, that's what we're interested in, turn over the main board to view the solder joints holding it down.
5. Solder a bridge between "GND" and "FMAGC" like I have in the photo bellow.
6. If your fault is the same as mine you'll now have fantastic fm radio reception!

[rwb]

Wow!
Very well done, and thanks for sharing. It's a common problem.

[Lee1978]

Thanks. As you said, the poor fm reception is a very common problem with these stereos, I'm not certain whether they all fail in the same manor but if they do, this is the fix

[Lee1978]

Anyone trying this fix, post to let everyone know whether it worked for you. It will be interesting to see if all these head units are suffering the same failure.

[Doggy]

Fascinating. I'm guessing what you've done either enables or disables automatic gain control? I'd like to understand if it's possible to explain without too much effort.

My FM reception was cr*p, but didn't improve with an alternate head unit. I got a big improvement by cleaning up the connections at the aerial and disconnecting the lead to the satnav, (which wasn't working anyway). It's reasonably good now, but not 100%. Just wondering if I should try this mod?

[Lee1978]

Doggy- my reception was completely useless on fm, even if I manually tuned to a known station the reception was still awful. It sounds like your issue isn't near as severe as mine.
If I were you I'd confirm the problem is the head unit and not your ariel by sticking a length of wire in the ariel socket (middle contact) and seeing if that improves issues, if it does the problem is clearly the ariel, if not it's the head unit.
If it looks to be the head unit at fault you can try the fix, you can test whether it's worked before putting everything back together as the stereo board will still function without the CD player, you'll just need to connect the front panel along with the plugs and ariel on the rear. If it doesn't cure your radio reception issue you can always put it back as it was.

[runner1]

Is it possible that in your case there was a dry joint and while reflowing and bridging the original problem was inadvertently solved?

[Lee1978]

In my case the problem wasn't a dry joint, the radios front end locked down completely due to the agc control going tits up, this was most likely caused by a corruption in the software that controls it. Agc is only usually necessary in am where a strong signal can distort the modulation, in fm we can do without it. The "fix" I've showed you removes the agc on fm and opens the front end back up.

[runner1]

ok, but I suppose the result might be that weaker signals are no longer received, or that you might get distortion in very strong signals. If it saves a radio though all is good :-)

[Lee1978]

Nope, no compromises at all. The radio will be just as sensitive as before with no loss of quality;)