Test Weak Play Motor ? NSM City-II

[rmacleod96]

Working on a friend's NSM City-II with DC transport motor AC play motor.
I have problems with play motor .  can i test it on the bench ?

i do not have easy access to the jukebox but i have the carriage 

The jukebox selects, loads OK,   doesn't play ,   rejects and unloads OK
same for side A or B 

when trying to play the motor runs slow and/or stops all together
turn table spins freely by hand , free spins 4 or 5 times times before stoping
motor spins by hand  1 or 2 times before stoping ( is this too much drag ?)
motor windings measure 180 ohms and 220 ohms ( should they be same ?)

Can i apply 40 Volts AC on the bench to the motor , is this safe for the motor?
Are there motor run capacitors ?
the motor seems to have very little torque. is this normal

I believe i have the correct carriage schematic but i cant find the schematic of
the Power supply /amplifier/centrale board ! at least not one i can read ..

i'm trying to determine if is electrical or mechanical trouble ,  cause i really
don't want to take the motor apart unless i have to !!

Thanks for listening. ,,, Rory

[jukenorman]

Hi Rory,
These motor winding resistances look about OK, in the UK we are on 50Hz and the windings are about 188 and 210 ohms. I think that motor should be more free when you spin it (more spins) - have you tried oiling it, see the sticky on oiling? I cannot see it being an electrical problem with the motor. There is a motor run capacitor and resistor in the circuit, I suppose at a stretch they could fail. If oiling the motor fails, you might have to strip it - there's a tiny clip locks the shaft in place. One of the problems you sometimes come across is that the motor labours a bit because it has been "lubricated" with WD40 and once it's in there, you can never get it out without dismantling the motor.

As a matter of interest, is it the Shure or Ortofon version of the City II?

Norman.

[rmacleod96]

It is the Ortofon version . i just spent some time working on the carriage and 
i get erratic resistance readings thru the carriage cct board , it seems the 
brown connectors  are oxidized and possible  poor reversing micro switch.

the jukebox hasn't been used or played a record in years , 
so the lubricant could very well be dried out 

are the motor run capacitors the .22 uF  C512 C513 ?  these seem to be 
snubber protection for the reversing relay contacts 

or are the run caps on the centrale board ?

i really want to try running the motor on the bench , what do guys think ?

i cant see anything in the circuit that should cause a problem, opinions please


 the cct board on the carriage appears to be "218 918" 

Rory

[jukenorman]

Hi Rory,
The motor run capacitor is 3.3uF (60Hz), C210 in series with a 10 ohm, 1W resistor, R220. I think they must be located on the power supply board although I don't recall ever looking for them! I don't see any reason why you shouldn't connect 40VAC to the play motor. You could use a strobe disc to check the speed. I seem to recall posting a 60Hz strobe on here previously for an NSM issue.

The Molex connectors that NSM used are quite delicate. Sometimes small screwdrivers or similar are poked up the connectors in attempts at cleaning and often distort or even break the Molex connectors. You might have to extract them to check. Often it's possible to re-form them but the worst case is replacement. A Molex crimping tool is expensive but it's fairly straightforward just to solder the wires if there are only a few to replace.

The large ESII Ortofon schematics that I have are not for a City II because I have discovered some differences when previously working on one (welcome to NSM!); they appear to be schematically correct but I have picked up differences on pin-outs on some connectors - but they have been good enough to get me by. You would get the correct large schematics from jukebox-world.de.

Norman.

[rmacleod96]

I sucessfully tested the motor

I found a suitable supply of 42 VAC  (using 2 X 20v wall warts).
i used a 4uF polycarbonate capacitor and a 10 Ohm resistor in series between pins 11 and 12 on connector 5
I applied 42 v to pins 7 and 16 on connector 5 . The motor spun up very well . when I replaced the little white nylon washer
on the motor shaft the motor struggled to start, It must be putting some drag on the motor ! This is without the turntable .
I have to reassemble and retry every thing .

The unloaded current draw is 120 ma and 130 ma   (FWD/REV)
The stalled current draw is 129 ma and 139 ma
Without the capacitor connected the motor makes no attempt to start and current draw is 100 ma
 
After reassembly i will retest and repost 

jukenorman is your strobe ment to be viewed with floresent light ?

Rory 


 

[jukenorman]

Hi Rory,
The strobe just needs to be viewed under any mains (60Hz in your case) powered light.

Norman.

[rmacleod96]

After reassembly all is good,  turntable seems to spin ok , I am able to switch directions 
of the motor just by manually moving the DS switch 

So the result is ,  you can test AC turntable motor with the carriage 
on the  work bench , but you have to use a donor motor run capacitor/resister network



Rory