Well I think so anyway...

It seems to need resetting after every record is played. It will play nromally, all the functions working as normal. When it gets the end, it returns but not all the way so it seems, you have to move larger of the white sliding peices to engage the gear in the cnetres, where upon it puts the arm back, and makes some unpleasent slipping gear noises. However once it has done this it will play as normal.. My guess is one or more of the gears is out of sync somewhere. Any ideas?

regards

Stewart

Oh dear.. its now copying monty pythons parott.. its dead, nothing works and no sign of life..

Hi Stewart,

Please download this article, go to Section 5, and follow the instructions exactly. Well-known manufacturing defect, with a cure!

http://www.condoraudio.com/wp-content/uploads/Projects/BeoGram-4500-Turntable-Restoration-Repair.pdf

Let us know how you get on.

Menahem

Hi, I have had a read, and have got as far as getting the piston out... however it is loose with no noticable friction on it and no signs of deformation yet, is this normal for this fault?

Stewart

Stewart,

That solenoid is THE key to getting the whole operation started. 

Even if it feels that there is no noticeable friction, there still may be more friction than the magnetic field is able to overcome.

Have you got "Silicone spray"? No WD40 or any other petroleum-based stuff!!!!

Follow paragraph 5 about the spray.

Reassemble the solenoid (it may not be the last time!).

Leave the platter OFF the unit.

Press PLAY, while gently pushing down on the central plastic weight sensor.

Does the piston move?

If not, (although this is a very rare failure) have you measured that when you press PLAY, there is an electrical signal at the solenoid? How much voltage?

If there is voltage, and the piston still does not move, then the piston is absolutely deformed, even though it may not look so, to the naked eye. There are VERY small tolerances inside that solenoid tunnel, and a tiny deformation WILL prevent the piston from moving.

Menahem

Hi, I just wanted to check that what I found was not unexpected.. but I have found a potentially bigger issue. I have the service manual, and have found no voltage at P3 (I belive it should be the 12v DC power input to the main board) I do have 19v AC at the fuse. This I think has to be resolved before any more investigations.. I suspect my original fault was due to this piston as the arm would move to position and not lower, whcih would make sence given the piston looks to move one way to start motion of the arm to position and then the other way to start the lowering of the arm. 

I can see how the soloniod starts things off, but the diagram would indicate that the main turntable motor would have to run as the soloniod moves? (if I am correct an the soloniod just engages one or other gear on the central gear)

OK, if you have no output voltage at the 7812 voltage regulator, it's clear that it's shot.

Now, it's a simple thing to replace a voltage regulator, but before doing that, you need to determine WHY it failed. These voltage regulators do not fail willy-nilly.

Assuming that the solder joints on the underside of the little PCB are OK, there are 2 likely causes. Either the big 1000uF decoupling cap is dry, causing the 7812 to ripple itself to death, or one or more of the 1N4002 diodes, which make up the full-wave bridge, is faulty.

If you've got access to an oscilloscope, you can determine the cause pretty quickly.

Menahem

Ok I have power again, ok not the way B&O intended, but its 12V and pretty clean. (Old AT PC suply 12V rail it will do while I aquire what I need on the orginal one, probbaly if anything cleaner) But its back to its tricks. I am pretty certain smothing has jumped its tracks though.

When in 'Play' mode the piston lever toward the back of the unit is sitting a good 3mm distant from the end of the piston and held there pretty solidly (I have not yet to force things as I find most such devices are alergic to broken plastic). The arm returns very slowly at the end of a record and stops several times (you have to press the stop buton to get it to restart and the piston flicks quiet happily when you do this). The white slider on the larger wheel does not move.. if you manually move this toward the turntable centre the arm starts to move at normal speed to its home position, however on the what the while slider hits a small triangular peice on the pulley wheel that moves the arm, and there is a nasty bit of gear slipping beofre it gets over this and all returns to normal..

Once in the 'home' position the 'play' button works perfectly as do the speed buttins and the lift/turn buttons (I belive these to be controled by the piston as well by inspection.

I am not sure if the piston is at fault, as it flicks about queit well (not sure the silcon spray made much differance to it!) I think somthing has jumped off its tracks somewhere as it seems to me that the lever that is sitting 3mm away from the end of the piston should be held against it, and when it flicks it should move the white slider to engage the main gear wheel. as it tands when in play this lever is held quiet solid and can't move the sliding peice  

I should have posted pics.. much easier to see whats going on or not!!!

these are of the deck in 'play' mode shoing the elver I mean. is it really supposed to be in this position? it stays there while the arm is moving back slowly, and I suspect is teh cause of this.

Found it...   that white plactic sliding peice was on 180 degress wrong...  I suspect the orginal fault was indeed excess friction (as the pistin is responsible for initialting the arm lowering), but my early investigations lead to that peice being put back in wrong, this possibly lead to the power supply failure (overloading when the gears were crashing) but now its right its all working fine, so once I have the PSU board fixed all will hopfully be fine. The piston was straight, any deformtion would show up when in the chuck of a lathe.... even if you can't see it you will when its spinning! but its been well and truly 'fixed'! now