I spent some time learning to program the small display that I integrated into my BeoloverRPM device that is useful for precision RPM adjustment as well as long term RPM stability characterization. I added min and max values as well as the total measurement time. Here is an impression of the display:
Quite high res and a nice contrast! However, guys of my age at least will need reading glasses to appreciate the small font...;-). Is life ever perfect??.
Anyway, I applied this new BeoloverRPM version to the Beogram 4002 that I just got going again and I performed a 12 hour RPM measurement. Here is the resulting graph:
This is a pretty good result about matching the specified 0.05% fluctuation number of the service manual. There are four spikes that exceed this specification (they are about 0.15% deviations). I have now measured a few 4002s with DC motor, and they all seem to have these spikes once in a while if one waits long enough. I think we see here the shortcomings of purely analog feedback systems. While these spikes are clearly measurable, they will be hardly audible. Most people can only detect changes of about 0.3 to 0.7%. So this Beogram should be fine for enjoying music.
Omg! Is that device for sale? I have a 4002 and sometimes the RPM is just a bit fluctuating. Mostly that is audible when I listen to smooth piano music, where the notes seem not so constant at times... I am looking to replace the RPM trimmers as well as the big capacitor. Is the big capacitor acting as a smoothing cap for the motor? So that it can run smoothly? Thanks for your reply in advance, Kees
ReplyDeleteYes, the BeoloverRPM is available to other enthusiasts! Just send me a message using the Inquiry Form to the right. Thanks for your interest!
Deletehi friends .
ReplyDeletei have repaired several 4002 and i have noticed that they suffer from motor bushing drying up .All you need to do is to soak them with motor oil .and pay attention to return the two sections of the motor to the same original position .otherwise the motor might turn in the opposite direction .the bottom bearing doesn't need to be removed as that end is
closed .just put a little of oil in there and let the bearing soak .Extracting the air of the bearing can also be accomplished with a syringe ,by introducing the bearing with some oil and push all air out first .Then keep the tip of the syringe close and pull the piston and create some vacuum .let it happen for 5 minutes .
The other problem on those turntables are the shafts of the mechanism..the original grease will dry up and the shafts will seize up .Easy repairs just remove the part with the whole running on the shaft and clean both with alcohol and a cut tip.After that add some lithium grease or a good lube .That it folks no money spent !
I forgot to explain that the motor bushings drying up is responsible for the motor speed FLUCTUATIONS is the only ,i mean the only explanation . Nothing else besides supplying the wrong voltage can be responsible .
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