NCT Controller described a possible MVA infraction during SOIA procedures when distracted by a sudden PRM failure requiring an immediate change to conventional approach procedures.

Narrative

SFO utilizing SOIA (Simultaneous Offset Instrument Approach) procedures; ILS/PRM 28L and LDA/PRM 28R. SOIA in use due to visibility instead of overcast layer (vis 5 HZ). A B737-800 was #2 for 28L behind a heavy B747; and was going to be paired with an A319 from over CEDES. I was focused on ensuring the B737-800 was in front of the A319 while still not too tight behind the B747. My trainee was monitoring me and preparing for his first SOIA session; only has minimal hours on finals. I was explaining to him the importance of keeping aircraft on vectors at a higher airspeed than the straight-ins to insure the 28L traffic in front by 2;100 FT. I descended the B737-800 to 4;000; I think. As I was preparing to issue the turn to final there was a loud pop in the area and an aural alarm sounded. The Wiley PRM had stopped working correctly and had turned off. I turned the B737-800 to a 280 heading and told him there would be a delay due to the monitor malfunction. The Foster Controller told me to just run the B737-800 in because he thought we could establish visual separation and issue visual approaches. Since traffic was light I elected to issue the B737-800 a left turn from a 280 heading to 030 which would take the B737-800 behind the 28R traffic. As the B737-800 was making his turn I observed him at 3;900. I issued a clearance to maintain 4;000; advised him he was outside of Bravo and would re-enter at 4;000. He climbed to 4;000 and landed at SFO without any problems. The B737-800 didn't enter the 4;000 MVA but he was right on the 3;000/4;000 boundary. I don't think I missed a read back when I issued the B737-800 4000. I may have missed the B737-800 reading back 3;000 when I issued the left turn to 030. I was very focused on getting the B737-800 in front of the 28R traffic and was distracted by the monitor failure and the technicians in the area and everyone calling for a Supervisor. I may have issued the B737-800 3;000 prior to the monitor going out and then forgetting about the altitude as I turned the B737-800 around. I was trying to force the B737-800 down so the FOSTER Controller wouldn't have to hold the 28R traffic to high prior to issuing the approach clearance.