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Old 9th Oct 2011, 5:05 pm   #6
Kat Manton
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Join Date: Jul 2005
Location: West Yorkshire, UK.
Posts: 1,700
Default The deck, specifics Part 2.

Idler Drive
The vast majority of old record players are 'idler drive' machines. This does exactly what it says on the tin; drive (from the motor) is transferred to the platter (the round thing you put records on) via an idler. Note that the idler wheel is sometimes known as the "jockey" wheel.

To accommodate different speeds, the motor spindle is stepped. Three or four steps may be encountered, rarely two.

The speed selector moves the idler up and down so that it aligns with the spindle step corresponding with the chosen speed. The largest step corresponds to the fastest speed, typically 78 rpm; the smallest corresponds with the slowest speed.

The operation control not only applies power to the motor, it also moves the idler so that it touches both the motor spindle and the inside of the platter.

Here we can see the idler of a three-speed record player with '33' selected and the the operation control set to 'off' and 'on' respectively. In the 'off' position, the idler isn't in contact with either the motor spindle or the platter, but it is vertically aligned with the smallest step on the spindle. In the 'on' position, the idler is in contact with both the spindle and the platter.

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Similarly, here we can see the idler with '78' selected and the the operation control set to 'off' and 'on' respectively. As before, in the 'off' position, the idler isn't in contact with either the motor spindle or the platter, but it is now vertically aligned with the largest step on the spindle. As before, in the 'on' position, the idler is in contact with both the spindle and the platter.

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What can go wrong
  • The inside of the platter and/or the motor spindle are dirty or contaminated with lubricant by some moron spraying WD40 wildly over everything on the assumption that a water dispersant carries magical repairing properties. The cure is to thoroughly clean both the stepped motor spindle and the inside of the platter (don't forget this bit just because you removed it and have the short-term memory of a goldfish) with IPA (isopropyl alcohol.) This is often the cause of slow or varying speed as the idler slips on the motor spindle and/or platter; it often causes the deck to grind to a standstill during an automatic change cycle.
  • The idler's surface has become hardened, glazed or crazed with age. As the diameter of the idler does not have any bearing on the deck's speed whatsoever, it is possible to remove the hardened/glazed surface with very fine abrasive paper without it affecting the speeds. The easiest way to do this is to spin the idler using a lathe or electric drill. This, too, is often the cause of slow or varying speed as the idler slips on the motor spindle and/or platter; it often causes the deck to grind to a standstill during an automatic change cycle.
  • The rubber motor mounts have decomposed, allowing the motor to drop lower than it should be, causing mis-alignment between the idler and the correct step on the motor spindle. There are several methods to solve this problem depending on the particular deck, so it may be better to ask. This is often the cause of "it plays at the wrong speed" faults.
  • The idler fails to make contact with either the motor spindle, the platter or both when the deck is set to operate. This is often caused by the arm which carries the idler being stuck. It should be free to swing back and forth. Dismantling, cleaning and lubricating is the cure. This problem results in a running motor but a platter which doesn't turn.

Belt+Idler drives

Ignoring more modern and professional decks with belt drive, there exist a small number of older decks (notably by Garrard, such as the RC80M to name one) which use a combination of belt and idler drive. In these, two small belts and an intermediate pulley are used to transfer the drive from the motor to the idler wheel.

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The required belts are becoming difficult to obtain in the UK and Europe, but are currently obtainable online from the USA. A web search will show a number of suppliers.
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