Power wave when switching on MM hd130

Hey!
I have a MM hd130 410. My tech has come across a problem that he hasn't seen before and doesn't know how to deal with. maybe someone of you does.
I blew a fuse recently when playing loudly and with multiple effects. Not the fuse you can access from the "outside". The light in front was still on but the speakers were dead silent.
My tech switched the fuse but when he switched the amp on for the first time his meters showed a "power wave" that very rapidly rose and disappeared. This only happened the first time he switched it on and he hasn't been able to provoke the thing again. For this reason he hasn't been able to understand really what happened. He figures that once I plug it in and play sooner or later it will appear again.
Any ideas?
Please also tell me if there are more specific questions I should ask the tech for you to be able to understand the problem.
Thanks!
/Jens

What meters? What was he measuring? Voltage? Current? Where was he measuring? Need a little more info. May have just been inrush from caps being discharged. Don't know. I'm assuming this is an export amp since the US ones don't have internal fusing. Mike