"les" writes:

Hello...
I have an old photo studio speedlight (Speedotron) that is
starting to buzz and overheat. Actually, it's the AC mains
XFMR, but as the unit warms...and the transformer starts
to bubble......yikes!, amazingly the strobe unit still works.
I'm obviously in need of a new transformer.
I know that old transformers tend to delaminate, but what other
maladies do they suffer?
Can they just overheat from failing insulation, or other aging issues?
I realize rising current draw could cause similar behavior, but I'm
assuming age as the factor in the transformer for now. Is this a foolish
assumption? (25 years old)

I'd guess there is a shorted turn.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.