I got 4004 recently, and the last thing I did was replace the belts. There is a problem that I had before, and has gotten worse now. Basically the platter is not flush with the top of the unit, and as a result, the bottom of the platter rubs on the belt, causing it to slap a bit and cause noise.

So I got out the service manual, and followed 3-1; mainly the "Height and side adjustment of chassis". I have gotten the problem to go away by adjusting the 3 nuts as instructed, to bring the chassis closer to being flush with the top of the unit. If I bring it all the way flush, I tighten the suspension to the point that it is too stiff to be useful, so I back it down a bit to compromise. I still have some issues & concerns with it however:

1. Platter is not perfectly flush with the top (though it is closer, and belt no longer rubs).

2. Turntable is not centrally located between the transit screw mechanism (as indicated in the manual. That's the 2mm measurement.

3. While the suspension still works, it is not as "bouncy", or soft as it was before.

I just want to make sure that what I did is OK, and I am not overlooking some other side effect. Any comments or pointers?

Thanks

Chris

Unfortunately, there are lots of wrong size belts out there.
The problem could be as simple as a too tight belt, it literally
pulls the subchassis towards the motor, blocking the suspension.

Martin

Chris:

Martin's got replacement belts for the 4000 series turntables if that's indeed what's wrong. They should be changed anyhow as all are geting loose and cracked. If you want to try this you should also change the belt that drives the arm.

He's a real boon for these things since its so hard to get parts from B&O now.

You really shouldn't have to tweak with the suspension screws unless someone has tampered with them before.

The height of the platter can also be adjusted at the center bearing. The one that I'm working on right now had a loose center bearing with a similar height problem to the oen that you describe. There is a brass hex nut that holds it in place. If you loosen it you can turn the brass bearing which raises and lowers platter height.

Assuming its not the belt as Martin suggests, you can play with this adjustment as it will not affect the suspension damping.

Derek 

Well, the platter being below the rest of the unit is not being cause by a tight belt, since you check this adjustment with the belt off.  If anything, the new belt seemed perhaps a little loose to my liking, but definitely not too tight.

However, adjusting the center bearing up as you suggest, won't this also shorten the correct 23mm measurement between the top of the platter and top of the detector arm? I checked that first off, and it was dead on at 23mm, and yet the platter was well below the top of the unit.  I guess the question is, how important is that 23mm measurement? Maybe a compromise between the two measurements?

And as an FYI, I have replaced both belts with PRB branded replacements, and both seem of good quality and fit.
 

Yes you need to ensure that the platter (between the ribs)  is 23mm from the top edge of the tone arms. This should be verified both at the outer edge and the center of the platter.

If it is dead on then you shouldn't change it.

OK - then it looks like my only adjustment to raise the platter (without changing the distance between platter and detector arm) , is what I have done already?

Is there any other tweak or adjustment that can be made?  Is there maybe some parts that have worn causing it to sag?
 

Hi:

You asked this question a while ago. I now have another solution for you.

I was working on a Beogram 8002 this weekend adjusting level height. In addition to the adjustment on the hex nut on the suspension, the platter level can also be audjusted based on the threaded rod that that holds the leaf spring in place.

But shifting the distance of the lower nut AND the threaded rod you can in fact shift the height of the platter without stiffening the damping on the leaf spring.

This is not easy to do as you will need to make several adjustments on each of the three leafs to get the platter to higher.

What makes it difficult is finding the right distance on the rod to set the lower nut which allows the platter to rise yet damp properly. It can be done with patience.

 Hope this helps!

Derek