ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
greetings once again,
I am in the middle of restoring a BG4000 - almost everything is fine except I can't seem to find the cause
of the vibration coming through the sub-chassis.
touching the motor feels quiet when mounted but certainly not when taken off the chassis and hand-held, the platter seems to spin free and endlessly when pushed.......!
needles to say the cartridge picks up those vibrations and answers with a grainy sound.
now the strange thing is:
when I tighten the 3 transport screws the floating subchassis is stiff but the sound is basically 'grainfree' as those vibrations seem to have disappeared ?????????????
now, shouldn't that be exactly the other way round ?
I simply can not pin-point those vibrations - what am I doing wrong here ??
thank you for your ideas
cheers, ALF
Could be several reasons;
Did you check the motor phase adjustment ? The motor depends on the platters inertia to run soft and even.
A too tight platter belt (one of them standard sized ones from Ebay that sort of works?) willpull the subchassis towards the motor which typically results in the subchassis rubbing on themain chassis at the tiniest vibration. The rubbing transfers to the platter, the record... your ears.Martin
Hello martin,
Thanks for trying to help :-)
I checked the motor as per SM but can not get the smooth symmetrical sine wave, no matter what I set the mot pot on ?!
But does that implicate the motor is faulty ??
I re-adjusted the sub-chassis as per SM, tried various belts but can not eliminate the vibrations!
To me everything points to the motor or is there something else I could have overlooked ?
Cheeds, ALF
This type of motor rarely fails. And if it does, it usually stops working altogether. But of course dried lubricants in its bearings couldprevent smooth rotation.Does the waveform change, when you adjust the trimmer ?Can you tell, if the correct setting seems to be just outside the trimmers range?
Martin
Hmmmmmm,
I double-checked the other BG4000 and its motor: fine symmetrical sine wave, so i measured correctly.
Yes, the wave form changes with the trimmer ajustment but only remltely resembles a sine -wave.
It is hard to say whether it would improve outside the trimmer's range, unless I replace the trimmer ??
At its lower end the voltage drops to about 3.x VAC
Would you go as far as changing the trimmer ?
ALF
I just changed the mot trimmer to a 10k one and ufortunately the answer is 'no'
There is still no smooth and steady sine wave to be seen - it looks a bit like a very untidy
Sine wave and it is bouncing up and down, indicating there is something else not right,
But what ???
Is there a non-destructable way to open and re-lub the motor ??
It can't be good for the motor to run on about 2.8 VAC, can it ?!
Cheers, ALF
Are the power supply voltages correct and clean?Did you replace the large can capacitors?If you did, you did notice that the one for the motor is a bipolar type, right?If all that is fine, you could try swapping the motor from the working Beogram.Martin
the supply voltages seem clean.
I did not replace the large can capacitors (yet) but there is the previously discussed
unavailability of the bi-polar 150uF 10V RMS capacitor, instead menahem was using a 220uF bi-polar cap on advice from a forum member ?!
are you suggesting I should replace the 4000uF and the 150uF capacitors first before thinking about the motor-swap ?
right now the motor voltage is set to about 3VAC.
it seems there is no way of getting inside the motor for lubrication without causing damage to the motor - would that be correct ?
Jacques
This kind of reminds me of my Beogram 4000 project. I did recap it first but after that was done I could only adjust the motor drive to have a clean sine wave with an RMS value of around 3 V. The result turned out to be the bad transformer. Frede told me he has started to see those old transformers starting to fail. The original transformer is epoxied together so unlikely to be able to repair it. I couldn't find a manufacturer to make an exact copy. My solution was to have a replacement, toroid transform made. That solution was due to the restricted size the transformer had to fit in the Beogram. The result worked well although I had to sacrifice not having a 200 VAC output secondary to drive the strobe signal. You wouldn't have that issue as your primary will be 220VAC, right?
-sonavor
I know,
the voltage is well below the specified one but I can hear the motor growling above around 3.8V, using my digital multimeter.
also look at the scope and can see an even more distorted sine wave above that value.
strange thing is, when I touch the motor housing I can hardly feel any vibration but can certainly see a very untidy signal on the scope,
jumping up and down in contrast to my other BG4000.
trouble is, I don't even have a clean sine wave at all, not even at 3V RMS
and yes, we have 240VAC down under.
I have red your post with great interest and admiration.......the other trouble is my isolated location and those special items like your custom made transformer would have to come from far away, shipped of course :-((
we wont mention the cost !
a faulty transformer had briefly crossed my mind but I was somehow focused on the motor.
You might pull the transformer and measure the secondary voltages to see what levels they are without load. Another thing you could do is swap transformers with the other Beogram 4000 you have. That would quickly determine if the transformer is a problem.
If you need a new transformer there might be some place down under that can make them, right? The cost for a toroid made here in the USA would run about $200 US dollars, then you would have to add shipping costs.
I will start with the 0 Cx capacitor package and replace that, the only problem is getting the exact value caps !
this is what I found as replacements:
150uF710V RMS with 150uF 35VAC monacor bi-polar
2000uF/15V with 2200uF 16 V Samwha cap
3000uF/50V with 3300uF 63 V Samwha cap
4000uF/25V with 4700uF 25V low impedance Panasonic
considering the wide tolerances manufacturers specify those replacements should not pose a problem ?!
of course all will have to be ordered from overseas :-((
once that is all done we'll see - in the meantime while I am waiting I am going to tackle the load-free transformer, if I can :-))
cheers ALF
No problem whatsoever with your component choice. Don't forget the caps and the trimmers on the main PCB!
Also, I'd test the transistors in the motor amplifier and sine wave generator.
thank you for your encouragement :-))
will take a while 'till i get the parts though.
I understand you are referring to the following transistors: 0TR 2 & 3 and 1TR 7, 8, 9 right ?