Inspect belt for damage. All ribs must be complete, no cracks across, no missing bits, not signs of shredding.

This will be a huge PITA on the 190 2.6, as the belt is pretty much under the radiator support.

If the front part of the clutch spins more or less freely, it's not locked up, the belt is slipping.

Very likely the tensioner is shot, but the only real way to check it is to release the belt tension and verify that the pointer on the housing moves back to the start position. If not, remove and inspect, likely you will find the rubber torn, meaning the "spring" is gone.

If it's been slipping, the belt will be a mess, replace it and the tensioner.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!