The BOSS FDR-1 produces a popping sound when played

To achieve a tone similar to Synyster Gates' A7X sound, you may want to start with the following settings:
Green channel:

• Bass: 5-7
• Mid: 2-4
• Treble: 5-7
• Presence: 5-7
• Gain: 7-8

Red channel:

• Bass: 3-5
• Mid: 3-5
• Treble: 5-7
• Presence: 5-7
• Gain: 8-10

When using the Boss MT-2 pedal, set the tone control to around 12 o'clock and the level to taste. This should give you a good starting point for a heavy metal tone.
It's important to note that these settings are just a starting point, and you may need to tweak them to suit your own personal taste, playing style and the room you're playing in.
Keep in mind that the MX112 cab will also affect the sound,so you may need to play with the eq settings on the head and the pedal to achieve the sound you are looking for.
Also, keep in mind that the sound of the DSL15H head with the MX112 cab will be different than the sound that Synyster Gates gets with his rig. However, the settings above should help you achieve a similar overall tone.

Here's the link to the info-
http://www.sweetwater.com/sweetcare/articles/roland-td-7-initializing-td-7-restoring-factory-settings

Is distortion changes like we turn the OD/DS selector (changes to Boost-Natural-OD1-Blues etc)?
If so, the OD/DS potentiometer need to replace.

If the changes are like increasing/decreasing GAIN/BASS/MID/TREBLE/LEVEL and also TYPE of pre-amp, then one of PREAMP potentiometer is bad.

Your best to order this item from Fender parts dealer. Here is one found with google:

http://www.darrenriley.com/fenderparts.htm

Open and look for broken solder at the jack... common occurence when people step on plugs or cables going into these. Also look for circuit board cracks around the connector and also around the power input connector.

It sounds like the sustain is stuck on as if a sustain pedal is active. You don't mention if you have one, however if you MIGHT have one and you have used a Roland pedal, that brand is reverse sensed and would cause note to remain on.

I have the Boss ME 50. Here's things to try. Use wall outlet to power the 25 instead of batteries. Have volume on amp up, volume on pedal all the way up, volume pedal all the way up(depressed), no gain on amp(use clean channel or clean setting if only 1 channel)effects on amp off(reverb, chorus, delay, boost, etc.) mid range knob below 5. only 1 pickup on, guitar tone knob all the way towards treble. If this puts you in the ballpark you can then make slight tweaks to any of these settings. What we're trying to do is not run a dirty sound from the pedal board into an amp with dirty settings. That double dirt often causes a muddy sound. Aside from that you can back off on various effects in the patches. My 50 has a list of the patches and factory settings, so if the drive, for example is set on 8, I might back it off to 4, or the compressor, or the delay, etc. If you like the sound save it. If not continue on. Start with the amp 1st. Higher output tubes(such as JJ's produce a cleaner sound. Also the demo you heard was not coming from your guitar speaker which may not be on the clean side.

There is not a sustainer as such - However you can use the Decay parameter in the reverb module.

1. Set the Module Selector knob to Reverb
2. Choose a reverb type from H = hall, r = Room, s= Spring, A = Arena, t = tiled Room (arena 1 - should do it quite well)
3. Turn the module knob to decay And rotate the value knob until the number 30 shows

Apart from that you may get a bit more sustain from using different Drive modules - the distortion drives such as Ed will give a longer sustain than the clean accoustic drive sounds.
Using heavier gauge strings on your guitar will also give longer sustain but make it a harder to play fast.

Plug your guitar into the input and a cord from one or both outputs to the inputs of whatever you are using. Meant to be run in stereo for best sound. Two guitar amps?

A good electronics store should have the part you need. I think its a rubber grommet that your looking for. They are round but become oblong looking once they're in place. Hope this helps.