Could still be a mechanical seizure, I have seen examples that barely move! You need to remove the panels and platter and operate the sol manually with your finger. If it moves freely with only the tension of the spring, then there is likely an electronic problem that needs to be looked at. You can also check that the solenoid looks healthy and not burnt up.

Thanks everyone, gives me the guts to go and click the frame open again.

The mechanism moves without a problem, so I will start going through the connexions around the solenoid.

There's no danger of me servicing it myself if things get any more delicate but I would, please, like to know any other causes of this problem and what I might have done to break it.

PF

If your Beogram 4002 is one of the types with one or more open switch contacts on a small board on the left side
of the carriage, one of these switches may be broken or bent. Often the frontmost one, which is the one
activated by the arm from the lowering solenoid.
It switches from solenoid activating current to holding current. If it never gives activating current, the solenoid
will not activate.

Martin

Well, thank you everyone for your ideas.

I have just spotted that I have a missing diode, the 1n4004 in front of the coil. It was probably knocked off when the platter was pushed down at some point: It does sit very close.

PF

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The diode IS fitted but it is on the underside of the board!!!!

D'oh.

Thought  I was getting somewhere then.

I'm going for the solenoid.

To respond to Dillen, the one switch I have appears to work perfectly but isn't ever activated as the solenoid mechanism doesn't move in the first place. The mech moves freely by hand.

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The solenoid coil should have a resistance around 8 ohms in good condition

I also just obtained a 4002 ( Type 5523 ). It has three problems. When I press start,the platter starts spinning at 33 RPM and the arm travels all the way to the left with the speed changing to 45 RPM at the correct time. When it gets to the end, it returns to the start without stopping. I can stop the arm using the < > buttons. It does this whether there is a record on the platter or not. The record detector lamp is lit.

 The arm doesn't drop at all and the solenoid doesn't click at all. I checked the function of the mechanical linkages and they all work smoothly with no old grease. I tested the solenoid  coil and it has continuity and a resistance of 9 ohms. I applied power to the solenoid coil and the solenoid functions correctly.

The third problem is that the arm doesn't move when it gets out of tangency. I moved the arm over a record and if I push it either left or right the tracking servo doesn't cause any movement.

 I pulled the control board and don't see any obviously burnt or damaged components.

 Are there any circuits that are common to all three functions that may be causing these issues ?.