Grandstream UCM6202 Repair Specialist

I need an expert to resolve registration issues on my Grandstream UCM6202, which occurred after a power outage. Basic troubleshooting has been attempted, but all handsets are still down.

Requirements:
- Diagnose and repair the UCM6202
- Restore account registration
- Test and ensure all handsets are functional post-repair

Ideal Skills:
- Experience with Grandstream products
- Strong troubleshooting and networking skills
- Familiarity with UCM6202 admin interface