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Monday, November 9, 2015

Beogram 4000: A Strange Solenoid and an Alien 7812 Impostor

While I am testing the repaired tonearm carriage of the Beogram 8000 by listening to my recently acquired early Genesis reissues (Trespass, Foxtrot, Nursery Crime etc...; they are available in a pretty decent German 180g pressing and come in their original gatefold sleeves) I decided to give the Beogram 4000 that came recently from Italy some attention. The most pressing item was its non-working solenoid, which looked strange and non-B&O:

I took the entire damper/solenoid assembly apart and had a look. Once the solenoid was out a nice handyman-job was revealed. I really appreciated the nail that was used as plunger to actuate the solenoid linkage

From the other side it is evident that the solenoid was soldered to the bracket of the original solenoid:

The nail required a modification of the linkage: A bolt was attached to the hole that normally takes the solenoid plunger:
The solenoid was probably weaker which inspired the handyman to elongate the original spring with a secondary one to reduce the spring face on the plunger...pretty crafty!

I cleaned and re-lubricated the damper

and the linkages and put the assembly back together. I replaced the strange solenoid with a solenoid I extracted from a Beogram 4004 that I recently obtained for parts. Luckily they are interchangeable:

Then I tried it out. And it did not work! The solenoid jerked briefly when the arm was lowered but that was it. I was able to manually push it down and it would stay down. Obviously not enough power for the solenoid. After a bit of head scratching and doing some measurements it became evident that the solenoid did not get the required voltage. I poked around a bit and if finally struck me that there was a strange impostor: A 7812 voltage regulator including ripple cap that did not belong:

So Mr. Handyman's solenoid apparently was a 12V model and he put the 7812 between the rectifier and the solenoid. The blue jumper was elongated with a brown lead and the red and black wires connect the regulator to the rectifier and ground:
Crafty! Strangely, I measured 26V at the solenoid and whenever it engaged the voltage collapsed to ~1.6V. This indicates that the regulator did not survive the solenoid back EMF when it turned off and therefore stopped regulating.
Anyway, I removed the set-up and reattached the blue jumper that supplies the solenoid with power to the collector of 0TR1:

And that did the trick. Now the solenoid is working as it should. This 4000 is back in business!
While Mr. Handyman obviously just knew enough to be dangerous, I have to give him credit for doing his deeds without creating a total mess. Everything was done in a pretty reversible way without drilling holes and cutting aluminum panels etc...So far so good. On to the next restoration tasks.

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