I have a problem with my DP-45F. When I press start the tonearm moves over to the record and comes down properly but the platter doesn't start. If I hold the Start 33 RPM button everything works, but when I let it go, the platter stops. It just started doing this after 20 years of play.

Don't try and force anything that won't move. Try this. With the power unplugged, place the tonearm over the record, if it will move freely, while rotating the platter by hand. Move the tonearm slowly over the surface of the platter until the end. Continue turning the platter by hand and see if the tonearm picks up and returns to the rest. See if that fixes your issue. For more information or further questions, please visit my website at audioserviceclinic.com. Thank you.

OK a blast from the past. There is a switch that is in the base which senses that the cover is closed and this unlocks the arm and disk motor can rotate. The reason that the disk rotates when the cover is up is because this allows the disk to spin up to speed before the arm comes down. Once the cover comes down the switch unlocks the arm and the arm then moves this switch also can stop the disk if the arm does not unlock.

Hi, at the base of the tonearm (left side) you will will find a rubber grommet or hole. Insert flat blade screw driver. Adjust until tonearm is lifting at end of record. Cheers john.

Hi, most likely the auto function needs resetting. With the power off turn the platter manually clockwise a dozen or so times. Power up and play. Cheers john.

Did it used to start when you lifted the tonearm?

Many turntables start when the arm is moved over the record.

Basically, like almost any other turntable.

Look up the recommended tracking force for your cartridge/stylus.

Unplug the power to the turntable.
Using the tonearm elevation control, raise the tonearm.
Manually move the tonearm in toward the platter.
Manually rotate the platter ClockWise a few turns to disengage any cueing mechanisms.
Set the Tracking and Anti-skating controls to 0.
Disengage the tonearm elevation control. The tonearm will either float or drop. This is why we have no power, just in case it hits the platter.
Adjust the counterweight until the tonearm floats exactly horizontal. Use the flat portion of the tonarm rest as a gauge.
Return the tonearm to its rest.
Dial in the prescribed tracking force and anti-skating. Play records.


Register with http://www.vinylengine.com/ and find the manual here...

http://www.vinylengine.com/library/denon/dp-47f.shtml

Basically, like almost any other turntable.

Look up the recommended tracking force for your cartridge/stylus.
Unplug the power to the turntable.
Using the tonearm elevation control, raise the tonearm.
Manually move the tonearm in toward the platter.
Manually rotate the platter ClockWise a few turns to disengage any cueing mechanisms.
Set the Tracking and Anti-skating controls to 0.
Disengage the tonearm elevation control. The tonearm will either float or drop. This is why we have no power, just in case it hits the platter.
Adjust the counterweight until the tonearm floats exactly horizontal. Use the flat portion of the tonarm rest as a gauge.
Return the tonearm to its rest.
Dial in the prescribed tracking force and anti-skating. Play records.

I can't find the specific turntable. Who makes it?

This should work with some modifications for your specific controls...

Make a note of the tracking force setting.

Make sure the turntable is level.

Unplug the power to the turntable.

Using the tonearm elevation control, raise the tonearm.

Manually move the tonearm in toward the platter.

Manually rotate the platter ClockWise a few turns to disengage any cueing mechanisms.

Set the Stylus Pressure/Tracking setting to 0.

Disengage the tonearm elevation control. The tonearm will either float or drop. This is why we have no power, just in case it hits the platter.

Adjust the counterweight until the tonearm floats exactly horizontal. Use the flat portion of the tonarm rest as a gauge.

Return the tonearm to its rest.

Dial in the prescribed tracking force on the Stylus Pressure/Tracking control. Play records.

Since there are no tonearm adjustments the only solution in the manual that comes close is to make sure the turntable is level. The other possibility is the no-brainer of checking the stylus cover is NOT rotated down, preventing the stylus from contacting the record.

A quick and dirty test of tonearm balance being too light would be to unplug the power and manually move the tonearm over the platter. Gently lower it to see if it floats in the air or lightly but firmly contacts the platter. That won't tell you if it is tracking properly but it might indicate or eliminate tracking force as the culprit.

Is the platter itself moving up and down or the record? It could just be the record's wear and tear (warped) which raises the tone-arm which in turn makes it move up and down on certain sections of the record. Try bending the record (very very slightly) to straighten it out or put more weight on the tonearm.

This turntable design has a direct drive system instead of belt drive (two types). If this unit has been in storage for some time, it has most likely been at hot or cold tempuratures - not good for any electronic/mechanical system. 
My guess is that the direct drive motor needs to be rebuilt - internal friction is probably keeping it from operating at proper speed. Best to consult with a repair shop that can handle direct drive turntables - several on the internet, if you cannot find one locally.

BTW: You can find a manual for this at : http://www.vinylengine.com/library/denon/dp-45f.shtml

Best regards,
Andre