Weak flash firing

I got my Metz 48 AF-1 out the other day and noticed it was seriously under exposing. When I pressed the trigger or manually fired it with the button on the flash it gives such a weak flash you can look directly at it without any effect.

Any idea what is wrong? Is it repairable? If not what is the equivalent replacement these days?

Is it in some kind of auto-flash mode ? Does it have a manual mode?