Sub how do i get to the sub settings?

If possible, move the sub to a different channel or amp. Or check a different sub on that amp to see if the same issue occurs. Also, check the crossover settings for the sub channel to make sure it is set to low pass, not high pass. If all of the settings look good and the issue occurs only with that sub on any channel/amp, then yes, there is a good chance the sub is damaged.

Is that the right part number, MCS 10, and not MCS100?

The MCS systems use a basic sub which is matched to the satellites. There's very few controls other than level on the MCS100. So as long as the power light is illuminated the there's very little other than the volume control that could be set wrong on the sub. So what it comes down to is either

1. a blown fuse (no power at all at the sub);
2. a broken input (#1 cable, #2 sub input socket, #3 blown sub plate amp);
3. incorrect connection at the receiver end or the wrong settings

As a quick test, unplug the sub cab from the amplifier/receiver end. Switch on the sub and turn the volume down all the way. Briefly put your finger across to short the RCA/phono tip and ring. The sub should make a buzzing sound. You now know that the sub is working and the cable appears to be okay

Switch off the sub and reconnect the phono/RCA to the sub out socket on the receiver. You now know it is connected correctly.

Go in to the receiver's menu and check the speaker settings. Is subwoofer present? Yes/No

Are the satellites all set to Small? (they should be with this system)

Are you playing a 5.1 source in DD or DTS to ensure that the sub gets a signal? Play a BD or DVD.

On the speaker balances, is the sub channel set to 0dB?

As long as all the above is set as listed, then the only things stopping the sub working would then be insufficient volume at the sub's Vol control (so increase it), or an intermittent cable connection (wiggle the cable), or a broken subwoofer out signal at the receiver.

With subs, it's either

1. a blown fuse (no power at all at the sub);
2. a broken input (#1 cable, #2 sub input socket, #3 blown sub plate amp);
3. incorrect connection at the receiver end or the wrong settings

You've ruled out most of this because another sub works in its place. So what's left is either sub settings, or a busted sub.

The sub settings for testing should be: Crossover frequency - Max; Volume - Mid; Phase - Normal.

As a quick test, unplug the sub cab from the amplifier/receiver end. Switch on the sub and turn the volume down all the way. Briefly put your finger across to short the RCA/phono tip and ring. The sub should make a buzzing sound. You now know that the sub is working and the cable appears to be okay or not.

Most subs auto sense a signal. So if the Sony isn't doing that then there's the problem. Given that these are very much a budget sub, I'd be inclined to have a look for something simple such as a broken solder joint or bulging capacitor. If it's anything more indepth then the cost to repair will outweigh the value of a replacement.

From page 84 of your user manual, the signal flow diagram shows that the two effects busses can be sent to the sub busses. You CANNOT send the subs through the effects unit since that would loop... so the effects that are selected from the channels onto the two FX busses which are then processed into the effects signals, then can be ADDED into the sub group signals. Make sure the subs are NOT selected to the mains and the solo of the subs is not set Nor is the sub mutes. You say the subs are showing signal... MAKE SURE THIS IS with the indicators set to display "Output" as that is the one that counts.. If the output when the sub is selected shows no signal, then likely the mute for the sub has gotten set.

hi,
if u want to hook up the sub with ur av receiver the connect the sub woofer output of ur AVR to any one (left or right) input of ur sub woofer. then connect its power . set the frequency range between 90 and 120Hz. set the volume of sub woofer to 40% of its total. also check the av receives speaker setting. goto speaker setup and make ON the sub woofer out.

if want to connect the sub to a stereo amp without sub out. then connect the amps speaker line to the speaker input of sub woofer and connect the speaker out of sub to left and right speaker ( make sure to connect the red to red and black to black). set the volume and frequency as above
ok

Connect a sub cable to the amps sub OUTPUT then to the sub input turn the volume up half way on the sub then go to the amp setup menu and make sure the sub is switched on then set the cross over to suit your speakers,if your not sure set to 80hrtz.

Hope this helps.

CABLE GUY.

Just had a look at both amp and sub on the JL Audio website. The amp runs from 1.5-4ohms. 4ohms at 14.5V. The sub is running dual 4 ohms coils. That's what the D-4 means. So should be an easy set up. The amp has two mono outputs, so one for each coil. It looks like the perfect wattage to run the sub real nice.
Web page for amp: http://mobile.jlaudio.com/products_amps.php?amp_id=439
Web page for sub: http://mobile.jlaudio.com/products_subs.php?series_id=18

MAKE SHURE YOU HAVE TOLD THE AMP YOU HAVE A SUB IN THE SET UP MENU UNDER SPEAKER SETTINGS.
IFF YOU ARE USEING SMALL SPEAKERS THEN SET THIS IN THE MENU AND OUT PUT BASS 2 SUB ONLY ,SET XOVER ON AMP IFF U CAN 2 120HTZ, ALSO CHECK THAT YOU HAVE THE SUB CABLE PLUGED INTO SUB OUT ON BACK OF YOUR AMP ,AND NOT THE 6 CHANNEL INPUT.
HOPE THIS HELPS.

CABLE GUY.

What type of deck is it?

Go into setup and make sure sub is turned on and set sub for LFE + main otherwise sub will only work with Dolby Digital LFE signals. LFE plus main setting will allow sub to output low freq's that would normally go to Front Speakers. Refer to Owners manual setup Info.