CUPERTINO,

Ca. – A key component of the Apple Watch made by one of two suppliers was

found to be defective, prompting Apple to limit the availability of the highly

anticipated new product, people familiar with the matter told the Wall Street

Journal.

The part

involved is the so-called taptic engine, designed by Apple to produce the

sensation of being tapped on the wrist. After mass production began in

February, reliability testing revealed that some taptic engines supplied by AAC Technologies Holdings of Shenzhen,

China, started to break down over time, the people familiar with the matter

said. One of those people said Apple scrapped some completed watches as a

result.</p>

Taptic

engines produced by a second supplier, Japan’s Nidec Corp. , didn�t experience the same

problem, the people said. Apple has moved nearly all of its production of the

component to Nidec, these people said, but it may take time for Nidec to

increase its production.

The taptic

engine is one of the key technologies that Apple created for the Watch, its

taps designed to be less intrusive than ringing, buzzing or other ways to get a

user’s attention.

The engine

uses a motor to move a small rod back and forth. This motion creates the

sensation of a gentle tapping. The taptic engine also powers another Watch

feature: the ability to send your heartbeat to others.

Apple last

week told some watch suppliers to slow production until June, without

explaining why, according to people familiar with Apple’s supply chain.

Suppliers were surprised because Apple recently said that Watch inventory was

insufficient, these people said.

An AAC

spokeswoman declined to comment about the company�s customers. A Nidec

spokesman wasn’s immediately available for comment.

It’s not

unusual for new technologies to encounter these types of problems in the early

days of production. But it marks the second glitch in a year with Apple’s

supply chain, admired for its ability introduce new products and boost

production quickly. Last year, Apple unwound an ambitious plan to make

synthetic sapphire after the operator of an Apple-financed plant in Arizona

filed for bankruptcy.

The

shortages highlight the potential downside of Apple’s lean supply chain. Apple

can produce massive quantities of products with little waste and excess supply,

but it can experience shortages when a problem arises with a key part.