Just bought an Anders all in one player. The 33 1/3 speed is slightly slower. Cannot seem to get it to run correctly. any ideas?

Question edited for clarity. Correct maker name (not Anderson) and full model description.

Just a motor and a tensioner.

https://www.google.com/search?q=anders+nicholson+model+f900+belt+replacement

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Lots of quality turntables have a speed checker and a limited amount of speed adjustment.

Many ordinary record decks use a synchronous motor, the speed of which is regulated by the Hz of the mains supply and with mostly fixed gear ratios it is impossible for them to run faster - slower is the usual problem.

I expect there will be types driven by a dc motor and regulated by a switch mode power supply but I know nothing about them.

I suggest you begin by learning something about your turntable.

Could be the belt for the pulleys is stretched a little, or there is something making it slip, or the potentiometers were set incorrectly from the factory . It is normal to have one for each speed. It is unknown if you can access these from the bottom of the unit. Slippage is less likely to be caused by something oily, since it would alternate the speed faster and slower and yours seems to have worked then reached a constant slower speed. Do your 45's and 78's play ok? (yeah I know, does anyone have a lot of 78's on hand)
Your model does not have an outside pitch control to fine tune the speed faster or slower. Another Jensen model JTA-230 does. Entry level turntables such as yours are not speed accurate reliable. After reading reviews on your turntable, it's possible that the belt is the problem. If the slow speed problem had happened from the start, it would be safe to say that the speed wasn't calibrated correctly and you could have returned it and perhaps had better luck with another one but because it worked fine at the start and then now plays slower, it's either the belt or the potentiometer for the 33rpm speed has somehow changed.

Try replacing the drive belt. Look under the platter for a 'rubber band' that would connect the platter to a drive motor. I bet it's loose. My other idea is crazy, however, they do sell an item called a "variac" which has a knob to control the voltage to the player. It's big and bulky and not worth the trouble. I'm a musician so I have to have a player up to speed or slightly detune my guitar. Good luck..

The answer lies in that 33 button. The connections to the should be followed and investigated why it does play correctly when held.

You may be experiencing Acoustic Feedback, although it doesn't really make any sense the way you describe it. Make sure the tonearm is balanced and the proper weight is dialed in on same. Does it make any difference if the volume or bass are turned down, which my point to the Acoustic Feedback.

Found this post trying to troubleshoot my Aiwa PX-E860U-after replacing the belt and lubricating bearings, the speed was off. 33 setting was playing slow. Here's the fix:
1. unplug and flip upside down
2. Locate the two holes marked 33 & 45 where black dots are visible underneath
3. Using a very small flat screwdriver(I used one from an eyeglass repair kit), adjust the speed clockwise for faster, counterclockwise for slower

this is a DIY solution, so not perfect, but it works. I played the tracks along to a Spotify recording to get a good match. Hope this helps someone else!

I have a different Sony model (PS-LX-150H) that had a similar problem. I hadn't used it in awhile, and then when I did, I noticed the speed problem.

IF your PS-LX250 is like my PS-LX150, there are small speed adjustment screws accessible from the bottom of the unit. On mine, the two adjustment screws were labeled - one for 33rpm, the other for 45 rpm. Basically I just fiddled a bit with them using a very small precision screw driver until I could verify that I had reached 33 rpm (I used a stopwatch and literally counted the number of rotations/minute after making adjustments.)

Now it sounds right!