Volvo: Odometer, bulb failure, volvo 850

Question
My car's (97, volvo 850) odometer stop rotating. Do you know what causes this problem and is that expensive to fix it? And the bulb failure warning light lights up. I checked all the bulbs, and all bubles are fine. Then what causes this problem? Thank you vecy much.

Answer
Rubin,
There is a gear inside the speedo that breaks. That gear is available through ipdusa.com The gear about $30.00.
If all the bulbs light up, then there is a set of bulbs that is mismatched. That means two parking or two headlamps that is not drawing the same current and that will turn on the light. Replace the bulbs in pairs and see how that does.