Neil- I talked to MidContinent Instruments & Avionics located in Wichita, Kansas last week. Ask for Bruce, as he is the TruTrak expert. I was told, if you have the blue screen, the repair cost is not so much. If you have the other screen the repair cost is almost the cost of a new unit.
The blue screen unit will have part #8000-164.
Hope this helps.
RV6, Christen Eagle II(Sold)
ATP, CFII, A-IGI, A&P/IA