Problem with a tray motor in a CD changer

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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-bin/catalog/e_catalog.cgi?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.

Re: Problem with a tray motor in a CD changer
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Sometimes if it uses a belt, the belt may be too tight - this will load down
a motor. Perhaps someone replaced the belt?

Or maybe a different mech problem. A wormscrew gear may have travelled on a
shaft. This could put a load on the motor as it tries to turn the gears.
Could be a lubrication problem somewhere in there too.

I think the motor itself is probably OK. Measure the resistance again as you
slowly turn the motor shaft. The resistance will vary as you turn of course,
but will settle down when you stop. Should never vary much from the 12 or
ohms when at rest, certainly never shorted or open.

Mark Z.



Re: Problem with a tray motor in a CD changer

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Sounds to me like a cap has gone south, Are there any caps that have
vented or buffy looking. check out the power supply caps, thats the
usual cause of slow motors othe than the motor it self

Re: Problem with a tray motor in a CD changer

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I had a look at all the caps - I've replaced caps before to deal with problems
in older gear.  This unit is probably only six years old so it'd have to be a
defect rather than normal aging.

I might check to see if there's a ripple AC voltage on top of the motor voltages
- that should tell me if it's a cap, correct?

Thanks for your advice!

MK.

Re: Problem with a tray motor in a CD changer

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Electrolytic caps that last 6 years in power supplies these days, are doing
very well, particularly as, for the last 10 years, designers have looked for
the hottest places on the boards to site them ... Ripple on the lines may be
a good indicator, but an ESR check is a better one.

Arfa



Re: Problem with a tray motor in a CD changer

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Thanks for your advice, Mark.  Actually there's no belt, it's a worm gear
turning a plastic gear which turns the platter.

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Everything is well greased, and I took the worm gear off the shaft and put it
back.  It runs freely when it's not engaged with the plastic gear, which itself
turns freely and is well lubricated.

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Good tip, thanks for that.  The motor looks good inside and the brushes are well
engaged with the spindle.

Thanks again,

MK.

Re: Problem with a tray motor in a CD changer

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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



Re: Problem with a tray motor in a CD changer

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Thank you, sound advice, when I get access to a variable supply that's just what
I'll do.

Re: Problem with a tray motor in a CD changer
Matthew,

    Could you please specify the model of the NAD?  Some models have had
driver transistor problems, though that doesn't sound like the issue
here.  I've also seen bad gears, and sometime the shaft on which the
gear sits goes bad, often from someone lubricating it with something
that 'attacks' the plastic.  Try spinning the worm gear on the motor by
hand and seeing if there is a stiff spot. as it tries to rotate the tray.

Regards,
Tim Schwartz
Bristol Electronics




Matthew Kirkcaldie wrote:
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