Working around a broken headphone jack...

If I'm mistaken on this, others are welcome to jump in and correct me.

The audio-out jack supports both analog out and digital (optical) out.

The digital/optical connector is shaped differently than a standard analog stereo mini-plug, and when inserted, it activates the digital/optical output.

The "red light" you see at times -is- the digital/optical output. When this is on, the analog output is OFF -- hence, no sound.

This sounds like your iMac is getting "unintentionally switched" into digital mode, even though you inserted an analog plug into it.

I'm thinking that perhaps the shape or size of your particular plug may be doing this.

Do you have a DIFFERENT plug you can use?

If you're plugging your headphones (or whatever you're using) directly into the iMac, you might consider an "extension cord" (has a plug on one end and a jack on the other) and use that "between" the iMac and your plug. Could be a "cheap fix" that works...

If that doesn't help, the USB audio adapter in post 2 might work.

There are also USB "DAC's" (digital audio converters) that provide excellent sound, but they're almost certainly more expensive...

This same exact thing happened to my 2012 MBP. My built-in speakers were disabled at all times because when a pair of headphones were not plugged in to the headphone jack, the system would think a digital audio cable was, and would disable the analog out.

Unfortunately, the only way to get it fixed totally is to replace the logic board.

As a cheap fix, you could try getting a cheap pair of computer speakers that use a mini-jack connection (same as a headphone connection). The computer would route the audio through them and not the internal speakers.

If nothing else seems to be working at the audio out jack, you could get some kind of USB-based audio adapter.

I believe you need to plug the USB adapter in, and then go to the sound preference pane and specify that audio output be sent via USB, and NOT through the [problematic] audio-out port...

Just wondering, the USB adapter you showed in post 2, where did you find that?

Gwaihir86 said:

Cheers!

I will order one and see how it goes. The one on the picture is just a random one from Google Images. I think I'll get a cheap one from eBay and if it doesn't work then I get an iMic, which is more expensive but compatible with Apple.

Click to expand...

FWIW, that one you've pictured is a SYBA SD-CM-UAUD adapter. Cheap, and quite good actually. I've used one and it works well.

I suspect that what has happened is that at some point you have put a bent headphone jack into the socket and have bent the little switch inside so it thinks you have a jack inserted all the time. This is usually fixed by gently poking about with a toothpick in the socket to bend the switch back so that it's not getting stuck.

If you can't fix it yourself with the toothpick method, you mentioned that you have had a go, it would be worth seeing if you can find somewhere near you that repairs audio equipment and see if they can have a go. In the meantime I would suggest checking any headphones that you use and stop using them if you see even the tiniest of bends in the jack as they will cause damage to anything that you plug them into.

And to clarify, as far as I know there is no workaround to get the internal speakers working without sorting the headphone jack.

Gwaihir86 said:

...
I tried to go to Preferences → Sounds → Output but by selecting the adapter I have to unselect my Internal Speakers, which means no sound comes out of them.

As I explained above, the problem is that the headphone jack seems to be broken and so the sound keeps periodically switching off, apparently because the computer thinks that there are headphones still plugged into the jack. I thought that by buying the adapted I will be able to get around the problem and that I will still be able to use the internal speakers.
….

Click to expand...

Not really true - no one yet has helped you with accurate information.
If your audio output port has mechanically failed, you can replace just the audio I/O cable, which includes the ports. That cable can be replaced - the logic board does not even get removed just for that cable.
Exact part depends on which 2009 iMac you have.
part number for the audio I/O cable is 922-9156 for the 27-inch
or 922-9127 for the 21.5-inch 2009 iMac.
Neither cable is more than $20.

iFixit has a repair guide, so you can see how to replace the cable.
https://www.ifixit.com/Guide/iMac+Intel+21.5-Inch+EMC+2308+Audio+Ports+Replacement/1980

Nice one DeltaMac, I hadn't looked into it further than the toothpick method as it has always worked for me when fixing this issue.

I would suggest that checking headphone jacks for bends is still prudent as otherwise the OP is likely to end up having the same problem again in future.

Gwaihir86 said:

…
Where do you reckon I should have it done? I phoned a company that repairs Macs (licensed by Apple) and the man, after I explained the problem, said it could be anything between £300-600 on top of the basic inspection which will then let them decide what to do. I thought that frankly that's way too much.

Click to expand...

An authorized repair shop will be best equipped to find out what's wrong - The audio I/O cable that I mentioned might not fix the issue completely, so I think it's reasonable to guess that the logic board might need to be replaced. After thinking about your problem, I think that a simple broken switch in the port would not be good, then bad, as you work. I would expect it to always fail.
However, it would be a good thing to try the cable first - it may be a good fix, and you should be out no more than the part (less than $20), plus maybe 1 hour labor - at the most.

Gwaihir86 said:

Thanks for all the replies. I was hoping the adapter will help but oh well...

CelestialToys, you might be right that earphones did it. But I don't use any earphones anymore because I'm afraid it will move something inside the jack once again It's very precarious and the sound switches itself on and off without me even touching it.

DeltaMac, thanks for the great advice. Looking at the website, though, I don't think I would dare to do anything like this. I would love to be able to but I don't think I would want to risk it. Where do you reckon I should have it done? I phoned a company that repairs Macs (licensed by Apple) and the man, after I explained the problem, said it could be anything between £300-600 on top of the basic inspection which will then let them decide what to do. I thought that frankly that's way too much.

Click to expand...

I'd try phoning about other PC repair places in your area, explain that you know what needs replacing and ask for a labour only quote...you can buy the part yourself and even show them the ifixit guide....don't let them tell you that it needs inspecting or that it could be anything else....your problem is definitely a physical problem with that part only.

CelestialToys said:

…
don't let them tell you that it needs inspecting or that it could be anything else....your problem is definitely a physical problem with that part only.

Click to expand...

Probably - but I won't agree with the "definitely, that part only". I'd have to see it first.

Then if someone sees those suction cups start flying around, it might make them hesitate about doing the repair. It's not too difficult, but likely not a good first try at a repair for some folks.

DeltaMac said:

Probably - but I won't agree with the "definitely, that part only". I'd have to see it first.

Then if someone sees those suction cups start flying around, it might make them hesitate about doing the repair. It's not too difficult, but likely not a good first try at a repair for some folks.

Click to expand...

With the number of combined optical/analog audio ports I have fixed with this exact problem over the years (some being intermittent as the OP describes) I'm 99% certain that this is the issue.

There is one sure fire way to ascertain that it is purely the switch and that is to plug some headphones in, if the audio continuously plays through headphones without any problems then I'll bet my house on it being the issue.