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 all,
Just wondering 'which' problem is brewing here, as the motor on one of my 4000 tables seem to get quite warm - not to say hot, depending on the running time ??
Is this just a lub-issue ?
This DC-motor is quite difficult to service, comparing that to the AC motor of the 4002 table !
Anyhow, advice is badly needed and hopefully not by a 'fire-fitgher' :-)
Thanks for your helpful suggestions
ALF
Hi Alf,
Can you hear it hum at all? It is AC by the way
Jacques
Hello jacques,
Good to hear from you and thanks for your reply.
I just disassembled the top to better hear the motor - if there is a hum it seems very faint.
Perhaps it will get louder the longer the motor runs as its temperature increases ?
I shall try that but there is definitely a difference between compared to my other 4000-table.
With the top-cover off I will let it spin for while longer as shall see how bad/hot it gets.
Cheers, ALF
Hi again,
Had the motor running for about 20 min and it definitely runs quite hot, however no increased hum or other unusual noises.....!
Question is: is it about to die or in desperate need of lubrication ?
If the latter is the case, what is the best way of taking it apart ??
Thanks again to all trying to help:-):-)
Check the motor phase adjustment.
Martin
Precisely what I had in mind Martin!
Hi martin - jacques
Are you referring to 'adjustment of voltage for drive motor' via Mot-1VR3 ?
Yes, that's the one.
Thanks jacques,
It measured 18.9V before adjustment and is now about 17.9V after adjustment
That should hopefully get the motor temperarture down?!!
But I will keep an eye on it
ALF: Thanks jacques, It measured 18.9V before adjustment and is now about 17.9V after adjustment That should hopefully get the motor temperarture down?!! But I will keep an eye on it ALF
I adjust by hear really, the motor shouldn't growl. You adjusted with an oscilloscope, and checked the sin wave?
Yes, look at the signal with a scope. Also, you are measuring P-P, not VRMS, right? The output should not be more than 6.5 VRMS. But check the actual signal with a scope to see how clean it is.
That is correct, p-p just under 18V which should be around 6.35VRMS ?!
sadly I do not have access to a scope :-((
There may not be a way around this, as the SM also speaks about an undistorted signal !??!
All I can do at the moment seems to lower the p-p voltage a tick ?
I take it that your digital voltmeter is set on AC, right?
The distortion thing refers to the sine wave which ought to be perfectly regular in shape, without any clipping. Do not forget that the motor is AC, like any old synchronous Airpax motor found on any turntable you can name.
Here this is a low voltage motor of the same sort.
At the top-right corner of the main board there is Mot-out.
First I measured DC between chassis (0) as per SM and Mot-out : adjusted 1VR3 to get 18VDC
Second I measured AC between chassis (0) as per SM and next to Mot-out - that showed 4.7VAC
As said earlier, I do not have a scope and felt a bit lost what and where against exactly I would have to measure VAC ?
I did follow you method though and adjusted so the motor runs as quietly as possible without growling.
Cheers ALF
This is the adjustment procedure I believe you are referring to. On the Beogram 4000 project I am currently restoring, I can only get the motor drive circuit to output a clean sine wave of 5 VRMS on 33 RPM and 4.69 VRMS on 45 RPM. The frequencies of the sine waves are dead on though (42.3 Hz and 57.3 Hz respectively).
I get about 6V on both frequencies. So John, are you saying it's not better than with the old transformer then?
It is better than the old transformer but didn't improve it up to where I hoped it would get. With the old transformer I was seeing the adjustment voltage drop below 4 VRMS to get a clean sine wave for both 33 and 45 RPM. The new transformer is pretty close to what I was getting with an external DC supply. A little higher actually.
Adjusting the Motor Phase correctly, requires 3 pieces of equipment, connected simultaneously.
1. An oscilloscope connected according to the Service Manual.
2. A Voltmeter set to AC Volts, connected to the same points as the oscilloscope.
3. A dim-bulb tester (100W bulb), in series with the BeoGram's mains plug.
As you are adjusting the phase and watching the distortion on the o'scope, you will see the dim bulb brighten and dim.
You want the bulb as dim as possible (lowest stress and therefore heat, on the motor), with the phase waveform as high as possible, without distorting.
The sweet spot will ensure a long cool life for your motor.
Menahem
The dim-bulb tester, being a series component, lowers the mains supply to the Beogram.If you ask me, final adjustments are usually best done under normal working conditions = normal mains etc..I suggest using a variac with a current monitor if you absolutely must monitor the mains current draw to get the adjustment right.The scope is usually adequate, maybe an AC voltmeter, that's what I use anyways, and when you've done a few, you can practically get itright by simply listening to the motor as Jacques noted.
Martin,
Of course that's right, but how many of the OP's here are going to invest in a variac?
My objective is to provide the hobbyists here with a user-friendly, simple and cheap visual method to understand what is going on, and a light bulb dimming or brightening is about the fastest and most understandable cue to grasping the operation of this circuit.
From my experience, a 100W bulb in this procedure does not have any appreciable influence on the voltage.
And of course, once the adjustment is done with the dim bulb, a recheck connected to normal mains AC power will confirm the setting, not requiring any further adjustment.