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Problem with a tray motor in a CD changer

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:

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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.

Reply to
Matthew Kirkcaldie
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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.

Reply to
Mark D. Zacharias

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

Reply to
David Naylor

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

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.

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

Thanks again,

MK.

Reply to
Matthew Kirkcaldie

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.

Reply to
Matthew Kirkcaldie

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

Reply to
James Thompson

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:

Reply to
Tim Schwartz

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

Reply to
Matthew Kirkcaldie

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

Reply to
Arfa Daily

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