Last week while taking some photos, my flash (420EX) went dead. Send to Canon Service Centre at Harbourlight. Was told that some internal circuits were probably damaged by the rechargeable batteries (new Sanyo 2500). The repair bills came to about $100. Went to collect today and show my international warranty card but without any receipt (as i have lost it). The service manager was kind enough to accept my explanation and we agreed that this will be the final FOC service for my flash. I would like to take this opportunity to thank him for his understanding of the whole situation.
I have learnt a few things from him:
1) Any batteries should be removed from the flashlight when not in use.
2) Register the warranty as soon as possible so that there will be a record in their computer system and preferably always keep the original receipt just in case. The practice of having unfilled warranty card should not be encouraged.