Where do you go for repairs when your computer is sick and the machine's maker is dead?

Sometimes, you're out of luck. You have become the proud parent of an "orphaned computer."

"Owners of orphaned computers frequently have no recourse but to start again and recoup their investment," said Richard DeSimone, chief executive officer of the Information Management Group Inc. in New York, which advises users with computer troubles.

"They can give the computers away to a computer technician school as a tax deduction," DeSimone said. "Let the students learn how to be a computer technician on one that doesn't work."

Thousands of consumers have spent millions of dollars on new computers and have been virtually left out in the dark for parts and service when their machine's maker went out of business or abandoned the product, some computer users say.

As of early 1984, about 205,000 people had purchased the orphan Adam computer that recently was discontinued by Coleco Industries Inc., according to Link Resources Corp. in New York. "They're in trouble," said George D. Green of Computer Doctors in College Park. "They're just not going to find the level of support they need to get work done on their computer."

Over 2 million of Commodore International's discontinued VIC-20 computers were shipped, but only about 674,000 people still owned them as of early 1984, Link said. "People just threw them away or dealers ate them," said a Link staffer.

Hundreds of thousands of people own the Atari 400 and 600 that were dropped by Atari Corp. "The Adam, Commodore and Atari computers are very difficult or impossible to repair," Green said. "That's the danger of buying the lower-end computers. All of the Commodores under $200 are difficult to get into, spare parts are hard to get from the manufacturer, and the cost of spare parts usually exceeds the cost of the machines."

About 1.2 million people own Texas Instruments Inc.'s 99/4A, which went on the market at $1,000 and was selling for less than $100 when it went out of production in 1983, according to Link. Timex-Sinclair 1000s, which were discontinued by Timex Corp. in 1984, were in the hands of about 525,000 people as of early 1984.

Manufacturers often assure their customers that they won't leave them stranded and will continue to service their machines. But they can't always fulfill that promise, because sometimes the dealers who sell the machines drop the lines or stop supporting them. To avoid getting burned with an orphan computer, experienced users suggest buying a computer from a company that you think will be around for awhile.

"I advise people to buy from a company that you're willing to bet on staying in business," said DeSimone. "IBM may not be the best computer, but it will be there forever."

Hundreds of thousands of people bought computers from Osborne, Franklin, Gavilan and Victor, which all have filed for bankruptcy court protection from their creditors.

Computer owners also recommend buying a computer that has a large "installed base" -- more than 100,000 machines already in use. With that large a base, independent companies often continue manufacturing parts even if the machine is no longer being made.

Some computer buffs, however, say that people worry needlessly about orphan computers. "There tend to be a lot of parts around," said Joel Makower, editor or author of four computer books. "They're not necessarily from the same manufacturer, but there are suitable parts from other manufacturers."

User groups, such as the Federation of Commodore Users Societies or the Capital Osborne Users Group, are also recommended as a good source for spare parts. Sumi Kinoshita, a member of the Greater Baltimore-Wasington Osborne Users Group, said she has never had a problem finding parts for her Osborne computer.

Xerox immediately began supplying parts for the Osborne machines after the company sought protection from its creditors, she said, and several members of the Osborne user club can fix Osbornes in need of repair. "There are always enough hackers around who take it as the ultimate challenge to find parts for the orphan computers or make them work," Makower said.

Another kind of orphan computer problem is the unused and unwanted machine, said DeSimone of Information Management Group. Many business computers become orphans because their owners never learned to use them or they never were right for the company. "In these cases, the computers are fine," said DeSimone. "But they become orphans as a result of bad planning and bad training."