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Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Monday, March 29, 2021

UPDATED - Beogram 4004 From Canada: Looking Closer At The Arm Lowering Solenoid Problem

After replacing the arm lowering solenoid on this Beogram 4004 with a spare solenoid (taken from a Beogram 4002 Type 5513)  I decided to look into how the old solenoid could be repaired. 

The only problem appeared to be that the solenoid plunger was sticking due to some magnetization of the metal components involved.  There is a current Beoworld thread that is discussing a magnetized Beogram 400x solenoid. Apparently there is a B&O service bulletin that acknowledges the problem.

I don't like fixes that are replacing a faulty vintage component with another vintage component. It means stealing a working part from another unit and there is no guarantee that the replacement part won't develop the same issue.

So back to this "faulty" solenoid.

In my previous post I tested the solenoid unloaded with a DC power supply and discovered it took 700mA and 7 VDC to get the solenoid to engage.

The good, replacement solenoid engages with only 300mA and 3 VDC applied.
Plus, the good solenoid operates easily every time without any resistance from the magnetized components.

I looked through my Beogram 400x parts bin and I had a bag of a completely disassembled Beograrm 4002 solenoid. I didn't remember that and I don't know where it came from.  However, it was a nice find :-).

Here are the solenoid disassembled components.

...and here is the "faulty" solenoid from the Beogram 4004 of this project.

As you can see, the arm actuator lever that attaches to Lever 193 (for the arm lowering damper) unscrews from the plunger.  I was able to remove the two pieces by using a padded vice on the plunger end while I rotated the arm actuator lever to unscrew it.

One part of the repair here is to demagnetize the plunger and arm actuator.
For that I used a tape head demagnetizer tool.

I treated the demagnetization process similar to the way I would demagnetize the heads of a tape deck.
With the demagnetizing tool about a foot away from the plunger and arm actuator I turned it on.  I moved the demagnetizer wand to the parts so it was touching them.  After moving the wand across the plunger and arm actuator for close to thirty seconds I retreated the wand back until I was about a foot away again. Then I turned it off.

After demagnetizing the plunger and arm actuator I reassembled the solenoid.
I placed a small nylon washer at the end of the plunger where it will strike the end of the metal sleeve that houses it. That should deter the problem from returning as there will no longer be metal on metal when the solenoid is engaged. I used some Loctite threadlock fluid on the threads during reassembly of the plunger and arm actuator.

UPDATE: In testing I discovered that using a 1mm thick nylon (M2) washer or using a 0.5mm thick fiber (M2) washer will interfere with the operation of the solenoid from the Beogram 400x control circuit. The end of the plunger needs to contact the end of the metal sleeve while the solenoid is engaged in order for the solenoid to stay engaged. For long term magnetic build up with these parts a head demagnetizer can be used to correct any sticking issues.

Now for the real test. 
I hooked the unloaded solenoid back up to my power supply to see what it now takes to engage it.

Very nice.  It requires less current than the other solenoid I used to replace it.

Of course this means I will have to change out the solenoid again and put this original back in.

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