Sound cuts out

This is the audio equivalent of video pixilation. It is caused by interruptions of the signal stream in the digital audio circuitry. And yes, it is hard if not impossible to diagnose. It is easier/cheaper to replace the failed unit than fixing it.

If your reciever is in a tight enclosed space, than it will overheat and shut down to protect itself. Try to get some ventilation to it by either opening the cabinet door, adding a fan, or pulling it completely out of the enclosed space.

You likely have a cold solder connection on the circuit board. Inspect the board for loose connections for the left channel - use a non-conductive pointed object and poke the board on several places while the unit is power-up. Be careful not to get electrocuted. Compare it to the right channel circuit - they are almost identical. If the unit recovers the left channel while poking, then you have found the bad connection. Re-apply solder to that junction - make sure you've dis-connected the power and dis-charged all caps before you touch and repair the circuit board.

the speaker is not broken, its the receiver, cuz i have this model, and now it just flashes a blue light on the power button and it wont turn on. I had the same problem as you before it did wat is doing now. i ran the speakers on my vsx-3900s, and they didnt mess up at all, they only did it on the vsx-816

try open each speaker test may be speaker or wire short....if all ok check pcb solder side....

Do you have the manual if not go here.
http://www.hammerwall.com/Manuals/Pioneer/Description/VSX-D608/Pioneer%20Home%20AV%20Receiver/L0020200/

http://www.pioneerelectronics.com/PUSA/Support/HomeEntertainment/AV-Receivers/PioneerReceivers/ci.VSX-816-K%7CS.Support

With the receiver off, press ENTER + ADVANCED SURROUND keys continuously for 2 sec. and it will tell you the fault it encountered. Even if it has a short, it will still protect the speakers; however, it is still a good idea to disconnect all speakers before doing this.

I had the same issue with the front right speaker randomly cutting out. Thought it was a loose solder joint however upon taking it apart i found that something near the back panel was shorting out. While apart i found that wiggling the rear panel would cut in and out the speaker. Also the fan would turn on when the speaker worked, which until i took it apart i didn't know it had a fan. I removed the back panel by taking out several screw the hold the cable plug-ins. once the panel was out i insulated it with electrical tape then used a utility knife to cut out all the cable connector holes. I also took out a couple screws on the main board so i could lift it a bit from the back and ran electrical tape over the solder point for the speaker connectors. Put it back together and haven't had any cut out's since. I now notice that the fan now runs all the time exept when i press mute. I also hear a single tap noise for a second when i mute or turn off the receiver. I can certainly put up with that though. Hope this helps someone else, I put up with the speakers cutting out for 6 months before i got around to taking it apart. Also those bannana plugs are a rip off, I went to future shop to buy them and couldn't beleive they were 25.00 for two pair. That would mean it would cost me 75.00 to do my 5 speakers. Thats more than i paid for my dvd player. anyhow i didn't buy them and just used bullet connectors, pack of 10 for less than 5.00, not made of gold but they work fine.