On 01/06/2013 18:20, Jamie wrote:

Also, if only supplies internal references, check to make sure the
connecting circuit is still using it. If not, the zener could be
clamping too much and operating hot..

Normally the evidence is showed with a over heated board that it's
attached to.


Thanks.

I'm not sure I understand the reasons it's used in this application
either, it's a 5W part and it seems to be used to create a 185v supply
from a 245v tap (+ bridge obviously) on the mains transformer. This
185v supply is then regulated by a comparator/series pass transistor to
160v. The weird thing is that even with the zener failed, the 160v
supply was still just about right, (it was at 163v).
Replacing the zener has put the 185v rail back to the proper value and
the 160v rail is now solid as well, minus the ripple.

The zener was mounted off-board with fibreglass sleeves on its leads so
they expected it to get hot Hasn't burnt the board though.
Replacement runs hot as well, but not uncomfortably so.

Lee