I have a halogen desk lamp with an internal transformer that recently stopped working (no light when switch goes on; fairly simple failure mode). The bulb still lights upon applying 12VDC directly, and there's no internal fuse I can see. Inspecting the transformer's internals, 120VAC shows fine at the input, and the dimmer pot appears to range reasonably from the range of megohms to zero.
The transformer is a fairly standard half-bridge design (in fact, it's almost textbook out of this application note down to the transistors used, which in this case are BUL39D's (and the cap is either C2/C3 in the schematic on p1).
The Cap In Question
I strongly suspect issues with either the cap, its corresponding transistor, or both, but the discoloration (more prominent when flash doesn't wash it out) makes me suspect the cap first. However, I'd like input on the following things before buying and trying a replacement:
- Am I reading the values correctly as 0.22 uF +/- 10%; 250V max?
- What type of cap is this in terms of construction?
- Other than needing to fit into a narrow space, is substituting a different type of non-polar cap with equivalent values likely to cause any problems in this application?