I need a good repair service for a Phase H20 back. I think I need a new firewire board. It is my understanding that Phase is no longer servicing these older backs. Any help would be great.
Why are you using a H20 back? My guess is that it serves you well and you are not interested in putting in a lot of money in digital backs.
If so it will with very high likelihood be cheaper to buy another H20, for example this:http://www.directdigitalimaging.co.uk/product/Phase%20One/Pre-Owend%20H20%20back/98
Repair will be ~€1900 - ~€2500 plus VAT, that example above is €1800+VAT. I'd say that he sells it for a bit too much though which is often the case for the super-old stuff. A 36x36mm sensor, tethering only, sold without warranty and no longer supported by the manufacturer, I'd say €1200 - €1500 (VAT already paid for) on the individual-to-individual market and since no warranty can be given in this case and you are an expert user a dealer provide very little extra value.
You can search the for sale forum. From there it seems that these were sold for ~€1400 in 2010, in 2012 ~€1300, unclear if they got them sold. When untethered 36x48mm backs can be had for €2500-€3000 there is not much market for tethered-only backs with small sensors.