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Beogram 8000 intermittent speed wow/flutter problem

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techpicky
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techpicky posted on Thu, Mar 30 2017 7:21 PM

I have been restoring my Beogram 8000 and have one last problem - intermittent speed fluctuations. It will be playing fine and then an audible slow down and recovery.  This doesn't occur all the time, it happens noticeably a few times at most for an entire side of an LP.  It is just enough to be annoying, but random enough that it will likely be difficult to identify the cause - thus why I am posting here.

I have already done a lot of repairs/restoration:

All electrolytic capacitors have been replaced.
Connectors have been resoldered.
Audio cable grounds repaired.
Tangential drive belt replaced.
Double stick tape goo removed and and replaced with new 3M foam tape.

A bit more detail that may help others restoring these machines, and cover what has already been done in more detail.

I had stopped using the Beogram 8000 when I had nothing but hum out of both channels, and the platter just hummed and didn't spin.

I assumed that the problem was electrolytic capacitors that were highly troublesome in European electronics from the era, especially the filter capacitors that have constant ripple current.  Given how difficult this is to service, and the history of these caps, I just changed them all including the one bipolar capacitor hidden in the power transformer assembly.

I changed the drive belt with one sold by someone on eBay selling - at a fairly high price - what he claimed is the right belt for the Beogram 8000.  It does actually work, but it is actually bigger in both length and thickness.  It does seem to work OK though.  I can give the info for the seller if anyone is interested.

The hum was caused by the audio cable itself.  Both RCA/phono plugs had crimped ground connections that had no continuity. I cut off both molded connectors and soldered on some quality gold plated RCA plugs.

When I thought I was done, I cleaned off as much old goo from double stick tape on the aluminum top cover, the lid over the tonearm compartment, and the shield under the plate under the tonearm rest area.  I replaced the tape with new 3M double sided foam tape.

After this I played a record and thought things were good.  I thought I heard some wow, but thought maybe it was the record itself as some artistic effect (it was a record I hadn't listened to in years).

The next time I went to use the turntable the platter motor just hummed again and didn't turn. After reading others online mention cracked solder connections (another fairly common problem) I very carefully looked, and sure enough the connection on pin 12 of the power transformer for the phase shift capacitor had almost microscopic cracks.  I resoldered all the pins on the transformer connector, all the other wire connectors, and anything else that looked suspicious.  I was really hoping the intermittent solder connection was the cause of the speed variations I had heard.  It wasn't, but at least the turntable turns again.

Now, as I wrote above there are intermittent speed variations.  These aren't extreme, and I doubt I could even see them on a strobe disc.  At least a few times a disc side there is an audible slow down and recovery that only lasts maybe a few seconds or less.  I don't have a test disc with a constant tone to more accurately measure wow and flutter.  These discs have become ridiculously priced these days, but I may still get one.  Recommendations are welcome.  With today's technology measuring wow and flutter is pretty easy, and someone created an analyze plug-in for audacity to do it without requiring any special instruments.  You can search for it - it is openly posted on another forum for vintage electronics restoration.

Also, if anyone has suggestions for how to get the dust cover to stay up, please provide.  I've already adjusted the adjustment screw to the max tension position, put 2 pieces of foam tape between the metal piece and the dust cover itself to make up for space from original tape, and make sure the cover over the tangental drive shaft tabs fit into the hinge.  It will barely stay up in the full open position, and any less (like when in the wall unit where it lives) it just flops closed.

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Saint Beogrowler
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It's probably the plastic tachodisc.

Peter-

techpicky
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Thank you for your quick response.  However the turntable I have has a metal tacho disk.  I'm not sure if it came with that originally, or was installed prior to me purchasing it used in 1982.  I bought it from a sales person that had bought it salesman special and used it for a while before moving on.  It was definitely opened at least once before I got it as the screw heads were somewhat stripped.

sonavor
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These Beogram 8000 and 8002 turntables can be a little finicky once they start to act up. There still could be signal connection issues you haven't found but you will probably need to start looking at a specific signal and trace it through. I believe the Beogram 8000 started coming with the metal tachodisc in later serial numbers. It is also possible the store refitted it with a metal replacement disc from B&O. Either way it is nice you can eliminate that usual suspect. The disc gets read by a tach sensor device though so you should check that the detector is mounted correctly to accurately read the disc. You might also monitor the signal from that sensor as it is what is providing the feedback to the speed control.

Regarding the tangential arm belt. I would stick with buying the belts from Dillen here on the forum. He has made sure the belts are correct for the Beograms and Beocord units he supplies them for.

It sounds like your dust cover lid is either not fitting correctly in the back or the mechanism isn't seated correctly. I would carefully take the metal hinge parts off and re-assemble it. If it is properly assembled the spring control will adjust to hold the lid up. This old thread has some disassembled pictures of the Beogram 8000 and 8002 dust cover hinge assemblies.

- sonavor

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