Speaker will play somewhat. the voices from the song will not play and it echoes a lot

If it was playing fine and just stopped working while you were playing it, it's possible the speaker has failed, or a wire has come off. It is likely something you cannot fix yourself, and should find a local music store, like Guitar Center, who can repair it for you. It's generally not a very expensive repair at all.

If the sound stopped working from one side after you were playing with some controls or editing some voices, you may have set the panning all the way to the right, which would cause no sound to come out of the left speaker. In that case, you would simply need to set the panning to the center again while in editing mode.

If you are not too familiar with the editing features on the PRS 330, and not sure how to set the panning to the center again, you could always simply reset the unit to it's factory settings once again, while will return all the voices, effects, panning, etc. back to like the unit was when it was first taken out of the box and turned on. Here's the process to reset the Yamaha PRS 330 back to it's original settings -

Restoring the default (factory-programmed) settings While holding the C7 key (right-most key on the keyboard), press the power switch to turn the power on.
This operation erases backup data in this instrument (including backup settings in the Function mode) and
restores the factory default settings. The User Songs and the external Songs stored to internal memory will be
retained

None of that works and you do need to have someone look at the unit, here is a link to the Yamaha Authorized Service Locator to find the nearest authorized service center near you -
Servicer Locator

Try to re-initialize the unit(factory reset). If the keys are the problem then the rubber key contacts need to be cleaned or replaced. Contact a local service center for help.

You have to plug in the laptop sorry to say. Think of it as a piano that can be used as a midi controller.

The control supposedly controls the mix of the echo... this is a reverb type sound. Please note that room acoustics AND if the mic's "hear" the speaker in this, it may create an echo that is NOT under control of the adjustment. Make sure the mic's cannot "hear" the speaker or a reflection off a wall.

Make sure you are NOT in looping mode. Make sure you do NOT have effects such as reverb inline to the amp and speakers. This will cause an echo of the note.

These speakers have a history of being blown if played too loud. Apparently the higher quality CX version are reliable. If the lows are what is crackling, the voice coils are probably cooked causing it to drag the pole pieces.

Open the unit and see if the wires to the speaker MIGHT be loose or making poor contact. The echo MAY be just the response of the speaker to the working one.

If you are driving the speaker too hard it will pop. This caused when the voice coil is driven mostly beyond the pole pieces of the magnet. Without the magnetic field the back EMF of the voice coil drops off and the current shoots up. The voice coil can't move farther so there is a discontinuity of movement which causes a pop.

200 watts is a lot to put into a 12 inch speaker so you have to be careful to not drive low frequencies at excessive volume. It is both very hard on the amp and doesn't do the speaker any good either.

If you want loud lows, you should get a subwoofer of at least 15 inch speaker to handle the lows.

You could record short "samples" to be used in building new voices, however, it does NOT appear that you can record a vocal song with the PSR9000. The Tyros II and III have the capability to record vocals but the PSR9000 and Tyros I do not..

When playing back an arrangement, you can re-sing the song and have the vocal harmonizer track the arrangement.

Several things to check:

If the speakers are cut off when externaal cables are connected to line outs, possibly the jack sensing switch for the right channel thinks that a plug is in there... you might cycle one in and out to see if that might fix.

Another thing is they LIKELY have a PAN control setting and it might be set full left. The external MP3 would NOT be under PAN control, only the keyboard voices would be affected by it.