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In Reply to: RE: Servo Drive Basstech 7 Repair thread! posted by ghaleon on May 24, 2008 at 18:17:37
A properly operating module, operated outside of the cabinet, will make some small amount of mechanical noise, most notably the "clicking" of the motor brushes as the shaft changes direction many times a second. Do not operate the module or complete subwoofer without a crossover high passed around 80-100hz. Have you used an air line with spritzer to blow any and all dust out of the motor, blower, the belts, arms, and generally any moving part?
The worst case scenario is what you have to check for-is the motor damaged?
You could have bad bearings, bad brushes, damaged commutator, overheated winding, or cracked winding. Typically, this means dismantling the motor from the drive shaft assembly, and get in your hands to look closely at it, and feel how it spins without anything attached.
Best regards,
John
Follow Ups:
Pretty much everything was blown off with an air line. The distortion kind of sounds electrical in nature… Up to this point, it hasn’t been tested with a crossover – I’ll use my EQ and just kill the frequencies above 100Hz. I’ll let you know when I’ve got the motor taken apart!
Thanks again!
Hi, can any body provide info on how to get belts for the servodrive basstech 7. Any info will be appreciated. thank you.
Taken apart is a dangerous phrase wrt this motor. They aren't really made to be dimantled anymore than servicing the brushes. I trust you meant removing the motor from the shaft assembly/mounting plate that it is attached.
Best regards,
John
Well, if I remove the motor from the shaft/plate and it's not spinning freely, or I suspect there's a problem, then do I really have anything to lose at that point?
I mean, apart from buying a new motor (which probably isn't possible?) I figure that it's basically up to me to do some small motor repair and disassemble it. I have a friend who is willing to take on the project. Do you have any other suggestions at this point John?
That looked like a fairly common Pacific Scientific servo motor. They show up on eBay regularly, and surplus dealers like Brigar sometimes have them. Use archive.org to see the old "Contrabass Corner" web site which had a list of compatible motors. From your picture, it looked like this is one of the off-the-shelf 0.89 ohm motors, rather than the custom made higher-impedance motors. Right now, there is in fact a new-in-box 4VM62 for auction on eBay.
My kit-built Contrabasses also have a "grumbling" sound that follows the bass. I suspect the neoprene belt or the pads take a set in the rest position, because I could feel a sort of notch when I rotated the shaft by hand. Some reviews also mention hearing this, so presumably it isn't just a flaw in my assembly.
Thanks for the info! I've included some pictures of the information plate attached to the motor.
This subwoofer has much more than a grumbling sound, it sounds like a kind of electronic distortion almost. There's a faint static sound, in addition to a pretty invasive distortion along with the bass.
http://i111.photobucket.com/albums/n148/ghal3on/Basstech%207/May8th08044.jpg
http://i111.photobucket.com/albums/n148/ghal3on/Basstech%207/May8th08043.jpg
This is the "original" Pac Sci motor. One other issue finding a surplus unit is making sure it has the 1" vent tube-many do not.
You can remove brushes and inspect them, two adjacent ones is the standard procedure(they are duplicates 180 degrees apart). Also, you may be able to inspect the commutator through the vent tube while it sits there still attached to the module and shaft assembly. It should look smooth, no pitting or chunks missing, with nice thin black lines between segments. You still need to remove the shaft assemble from the motor to really get a feel for the condition of the bearings, and ease of spinning(should be "like butter".
Best regards,
John
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