"Matthew Kirkcaldie" wrote in message
...
Hi all,

I'm trying to repair a NAD CD changer - everything works properly except
the tray motor is seriously underpowered. It tries to rotate the disc
platter but generates a pathetically small force, so that the tray moves
very slowly if at all.

I've checked everything mechanically for smooth operation, etc. The
motor is a Mabuchi FF-130SH, specs:
http://www.mabuchi-motor.co.jp/cgi-b...i?CAT_ID=ff_13
0rhsh

The player is trying to drive it in the forwards and backwards
directions by applying DC voltages, which measure about 3.9V DC and -3.9
V DC as the player tries to spin it backwards and forwards. In-circuit
the motor resistance is about 12.5 ohm, implying it's seeing about 0.3A
(right?). So with a listed stall current around 0.5A, does that imply
the player is unable to give it enough current to move? Or is the motor
resistance too high, preventing the applied voltage from driving enough
current? Sorry if these questions are naive.

I've opened up the motor and the brushes look fine - I've cleaned the
spindle with Deoxit followed by lubrication with Pro Gold and the motor
appears to be spinning freely - it runs smoothly with no load. However
when it's reassembled the tray barely moves.

I don't have a service manual for this unit but I am wondering if this
is a commonly used motor that people may have experience with - I'm
wondering if I should source a replacement motor, or try to figure out
why the CD player isn't delivering enough current. As I say, all the
other CD player functions appear to work normally, including opening and
closing the multi-disc tray.

Any advice would be very welcome - thanks in advance for any help
someone may be able to provide.

Thanks,

Matthew.

Use a battery or if you have it a variable bench power supply and drive the
motor with that instead of the control circuit. Disconnect one side of the
motor wire from the circuit before hand. If the motor runs fine then, you
will know it is the drive circuit . In diagnosing devices, it divide and
conquer. Eliminate the obvious. Jtt