My HSI in flight turned about 90 degrees off course. It was still somewhat functional just 90 odd degrees off though intermittently I would get a heading flag. I went to the GPS as a backup for heading information.

I attempted to use the slaving unit to reposition the HSI with no luck.

I took it to an avionics shop and they naturally sent it into King for repairs. They confirmed my slaving unit was dead and said it would need to be replaced. They installed a loaner unit.

First thing I discovered was the loaner glide slope was not functioning.

Second thing I discovered during preflight was my controls were jammed. Yikes.

Turns out a wire from the slaving unit was tangled in the controls. The person who unjammed my controls repaired the broken wire and voila, the slaving unit was functional once again. No surprise when King sent back my HSI and could find nothing wrong with it.

So... If your HSI turns off course and your slaving unit is dead have the avionics shop check the slaving unit before they send your HSI off for needless service. I did end up with two new shiny knobs on my HSI to the tune of about $130 in addition to the avionics shop labor charge and King's service charge! I would have been perfectly happy with the old knobs thank you very much.