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Wednesday, August 2, 2017

Beogram 8000: FOD Bites Me In the ***

Having a little experience in the aircraft industry I know about the acronym FOD (Foreign Object Debris). This post is an example of why the term exists and how it can even apply to turntable restoration.

In my recent Beogram 8000 restoration I was extremely happy with the final results and shipped the turntable back to the owner. Although the packing was as good as it could be there was undoubtedly a lot of vibration during the truck journey. When the Beogram 8000 arrived back home the owner noticed the tonearm was drooping. That should never happen. After failed attempts to solve the problem by phone the Beogram had to be shipped back to the workbench.

As soon as it arrived back I unpacked up the Beogram 8000 and saw that the tonearm was still drooping down instead of level with the fixed arm.  I put the Beogram into service position and the tonearm popped back into its normal position. That always happens doesn't it?

The question is what could have been causing the problem?  I started examining every detail of the arm lowering and raising parts. It is natural to suspect the arm control solenoid and some electronic control but this Beogram had extensive bench testing without any such incident. I was pretty sure the problem was mechanical.

Here are some pictures of the Beogram 8000 arm lowering/raising parts.

I exercised the arm lowering and raising manually to see if I could feel any restriction but everything was nice and smooth operating. I also powered up the Beogram and operated the Play/Pause/Stop functions a number of times while observing the solenoid action. No problems there. I wondered if something in the tonearm linkage just slipped a little during shipping and now it is all okay.

One new thing I did notice about this Beogram was that the tangential arm carriage drive was noticeably louder going forward than returning to the parked position. Of course I remembered that this turntable had a broken tangential drive shaft bearing. I had reversed its position and it worked fine while it was here earlier. I didn't discern any difference in the tonearm scanning (noise) at that time. However that damaged plastic lip on the bearing must be the source of why one scan direction is now louder than the other.

So while I hadn't found the source of the tonearm drooping problem I felt I needed to go ahead and fix this tangential drive noise issue. I had one spare drive bearing remaining in my stock so I grabbed it and prepared the install. This operation means taking the tangential drive off its rails and flipping it over to get to the bearing. While there I can also examine the tonearm lowering and raising components from another angle.

This is where I discovered the prime suspect of the tonearm problem. A piece of FOD was visible near the arm control lever.

That piece looks familiar! I looked at the tangential drive bearing and sure enough, that is the piece that had broken off the bearing...probably years ago.

If that small piece of plastic had shifted into the slot that the tonearm lowering bar slides in it could easily have caused the problem where the arm would not fully raise. I can only surmise that is what happened but it seems highly likely. The Beogram hadn't and still doesn't exhibit any bad behavior with the arm functionality. I don't think it is a coincidence that this plastic piece was in the location I found it and it not be the prime suspect.

I installed the new, fully intact, spare drive bearing and the tangential arm scanning operations are smooth again.  They operate with only the expected, soft whirring of the motor.

Now for the important lesson (re)learned about FOD. Seeing that the original bearing had a broken piece off the lip I should have done a more thorough inspection of the Beogram to search for it. I had just assumed it was long gone. On the Beogram 400x turntables where their transport lock bushings are often deteriorated into a thousand pieces I have to do a full cleaning of every part. This incident shows that even one broken piece of plastic debris can cause problems.

I am an optimist though so I take the view that this was a good learning experience and this Beogram needed the drive bearing changed anyway so it worked out good. It is time for a quick play test then I will ship it back home again.

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