The stereo in my 2000 Blazer started acting up a couple months ago. I use an FM transmitter and listen to my iPod through a 'dead' frequency. Over time the gain gradually weakened. At max volume on the factory head unit I could barely identify what was playing because standard road noise from the highway drowned it out.

One day out of nowhere the transmitter stopped working. My first thought was the transmitter crapped out. I tested it in our other car and it's tip top. Then I noticed that igot not volume on any FM station. Not even static. Just dead air.

It is not a bad aerial or tuner ... when I press the scan button the stereo grabs onto all the local signals, there's just no volume. The BIZARRE thing of it all is that the AM band works perfectly. What's more is that it's louder than bombs. That tells me it's not the speakers (which I replaced in the past year).

I work for a radio station and this has even baffled the in-house engineers. Any thoughts? I have no qualms albout replacing the head unit, I just want to make sure that it will have FM once it's installed.

 

The factory head units are notoriously failure prone. While I've never had your specific issue with one- it seems very likely that it is the issue. I can't see any other point in the system that could be failing to cause the fm band to drop out completely.

 

Beyond the head unit you only have the wiring (power, speakers) None of that would cause that to happen, as I am sure you area already aware of.
The HU is toast, put in a new one

 

You can try to pick up a replacement (OE) radio at a wrecking yard. That is what I did when my radio crapped out and caused a short that disabled many of the gauges on my instrument cluster and HVAC system. I found two nickles in the radio that I can only guess were put there by the PO's kids. I suspect these had finally got knocked loose and shorted something out.

On eBay you can buy refurbished OE radio/CD players in which the seller has added an AUX jack for people to connect players and phones.

 

Welcome to the world of cold solder joints