Samsung's engineers STILL don't know what causes the firm's Galaxy Note 7 to overheat and explode

Samsung's engineers are still unable to pinpoint exactly what causes itsGalaxy Note 7 smartphones to explode, it has been revealed.

Following the first case inAugust, hundreds of employees to were tasked with quickly finding the problem, and the firm initially blamed faulty batteries from one of its suppliers.

After announcing its first recall of the Note 7 devices in September, it decided to continue shipping new Galaxy Note 7s containing batteries from a different supplier.

However,last week these too began to explode.

'Company engineers went back to the drawing board, according to a person briefed on the test process who spoke on the condition of anonymity because the internal workings were confidential,' said theWall Street Journal.

'As of this week, Samsung's testers were still unable to reproduce the explosions,' it said.

On Tuesday, Samsung said it was killing the Galaxy Note 7 in an unprecedented move that could cost the firm $17bn.

It still has not disclosed what caused the Note 7s to smoke and catch fire — or even whether it knows what the problem was.

Initially, the Note 7 got glowing reviews for its size, features and big battery capacity. Now the company is struggling to figure out what exactly is wrong.

'They have to comprehensively check everything from the very basics, outside the battery and inside the phone,' said Park Chul Wan, a former director of the next generation battery research center at the state-owned Korea Electronics Technology Institute.

Park has long argued that Note 7's problems appeared to be more than a simple battery defect.

'This is a truly difficult problem. It was Samsung's mistake to have underestimated it,' he said.

South Korean safety regulators says they are examining components other than the batteries to try to puzzle out why even the replacement phones Samsung made using different batteries are so fire prone.

'The improved product does not have the same defect.

'That's why we think there is a new defect,' said Oh Yu-cheon, a senior official at the Korean Agency for Technology and Standards.

Samsung has received at least 92 reports of Note 7 batteries overheating in the United States, with 26 reports of burns and 55 reports of property damage, according to information posted by the United States Consumer Product Safety Commission.

Earlier this month, an independent lab posted images show a Samsung Galaxy Note 7 exploding into flames after pressure was applied to the lithium ion battery

Samsung's troubled Galaxy Note 7 has been subject to a mass product recall following reports of exploding batteries.

However, the lab responsible for the test has since claims that 'any phone' would suffer the same fate if subjected to the test.

The photos emerged just a day aftera replacement model reportedly began giving off smoke inside a plane.

The incident occurred on a Southwest Airlines flight to Baltimore from Louisville, Kentucky.

The test was carried out at the Applied Energy Hub battery laboratory in Singapore.

'Any pouch cell lithium-ion battery on any phone subjected to a heavy load will puncture over time, causing an internal short circuit,' said Jan Geder, Head of Laboratory atApplied Energy Hub in Singapore, where the test was carried out.

'We are certain that the same test applied on any lithium-ion battery in any phone will yield very similar results given the sufficient mechanical pressure applied; not just the Note7.

'During the test, a blunt nail was pressed directly on the battery while the rear part of housing was removed before.

'We emphasize that it is highly unlikely that the conditions of this test can be achieved under regular phone use,' said Jan Geder, Head of Laboratory, Applied Energy Hub in Singapore.

The images shows the device giving off smoke before exploding and bursting into flames.

Photos showing the aftermath of the explosive test reveal the charred remains of the smartphone and its battery.

The conditions of the lab test do not replicate the nature of the malfunctions experienced by Note 7 owners.

However, Samsung has faced harsh criticism following the emergence of the potentially dangerous product flaw involving overheating of the Note 7's battery.

Some of the toughest criticism levelled at the Korean brand has been over its fumbling of the recall, reports Reuters.

It warned affected users to immediately turn off their phones only after the same warning was issued by the U.S. consumer protection agency.

The regulator criticised Samsung for not following proper recall procedures.

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