JVC AL-E300 Turntable

see if this link helps you out. Tips for Repairing Your Home Turntable ..
or this one.. JVC AL E31 Turntable doesn spin automatically Google Search

There are some sellers on E-bay selling JVC turntable power supplies. You could try them.

Does it restart if you manually lift the arm up?
If it does then you might have not put the belt on right. Another reason is that the problem was not the belt, but a motor showing the signs that it wasn't coping when under load. This could be caused by grease or muck inside the motor or in the drive functions. However the motor could be faulty.

Probably as long it produces DC. However you will have to adjust the speed. As the unit was set for a certain voltage which wouldn't change. It will either go fast or slow depending on what the original voltage was. The speed adjuster will either be two presets one for each speed that could be located under the turntable base (covered by a sticker) or on the power board of the deck. Or they might be on the motor itself.

Even if the belt looks fine it's almost certainly the problem. You mentioned "cleaning" - if you got any kind of fluid on the belt it might act as a lubricant and reduce the friction between the belt and the drive wheel, causing the turntable to slow when the tone arm puts a drag on it. The problem may go away when the belt dries out.

To replacea turntable drive belt.Copyright.. Styluscity.com, JohnHarrison. Nov 2011Before starting any work on yourturntable disconnect it from the mains power supply.Remove the stylus or completeheadshell to prevent any accidental stylus damage.1. Remove the rubber platter mat toexpose the platter.
2. Put your thumb and forefinger through the two round holes either side of thecentre spindle and lift the platter off. You may need to give the centrespindle a light tap (whilst applying upward pressure) with a screwdriver handleor some similar tool that will not leave any marks or damage.
3. Remove the old belt and wipe the platter and motor pulleys with an alcoholswab to remove any old belt residue.
4. Place the new belt around the platter pulley making sure it is sitting flatwithout any twists.
5. Flip platter over the right way up. Acorrect fitting belt will stay put and an over belt will fall off.6. You will see 1 or 2 largerectangle or square shaped cut outs in the platter near to the outer edge. Throughone pinch up the belt and slip a finger or belt hook between the platter pulleyand the belt gripping the belt ready to fit over the motor pulley.
7. Align the centre hole of the platter with the spindle and place platter backinto position keeping a grip on the belt.
8. Slip belt over motor pulley and give the platter a light clockwise rotationto ensure the belt is riding correctly.
9. Replace the rubber mat and then run the turntable to ensure correctoperation.MUSIC IS LIFE, LIVE IT LOUD.Styluscity.com cansupply replacement drive belts for all turntables

hi, maybe you hve to replace the tack switch of your turntable even thougr you switch but the contactss maybe not in the connection,,

http://www.archive.org/details/Turntable_Belt_Installation

archive.org above has a video about how to do it. The general method shown applies to just about any turntable including your JVC

where can I get an 11V -13V DC adaptor to power JVC turntable AL-E300?

I have just fixed this problem on my Aiwa PX3800 with improvisation.
The platter was rotating too slowly, I didn't know how much too slow only that the records sounded wrong.
I imagined the belt, motor and platter as a bicycle gear and so simply increased the gear... I achieved this by winding a thin strip of a electrical insulation tape around the motor head to increase it's radius (like changing up to a larger front cog on a bicycle gear).
I could then time the rotations and remove a layer or two of the tape accordingly until I have achieved a perfect 45rpm. 33 is still way out but I only listen to 45s!
Be sure to trim excess tape from the motor head with a craft knife/scalpel or it'll stick to the platter.
Poor man fix up.