SCT Controller reported transmitter failures that resulted in an aircraft entering a higher MVA and in a CFTT situation.

Narrative

I was working controller in charge (CIC); we had issues with Fillmore Radar (FIMR) frequency/position. Person A was working FIMR position; we had just returned the FIMR scope to the actual FIMR scope; we had been operating FIMR at Glendale Radar (GLNR) due to intermittent frequencies. We had been operating on Emergency Communication System (ECS) 135.05. The tech had reset the transmission on ECS 120.4 (it was inoperable and in alarm) we tested the frequency with two aircraft. It appeared to work; Aircraft X was being vectored to VNY ILS final. When suddenly he could not hear any transmissions. He went through final at 050 into a 060 MVA. Aircraft X called VNY Tower; he told VNY Tower that he had the field in sight and they cleared him for the visual approach. Recommendation: We need an operable frequency for the FIMR position. For about the past six days frequencies have been intermittent. 120.4 Primary; standby; BUR tunable; 135.05; etc. are all out of service. 120.4 ECS is unreliable and had dropped earlier in the day and throughout the week. We tried 119.85; it did not work. So we moved the FIMR position to GLNR scope and used 135.05 ECS. Later on we moved FIMR position to FIMR scope and utilized 135.05 ECS. As I typed this up we had a separate TCAS RA on this position due to the aircraft not hearing the controller. The ECS frequencies are not strong enough nor designed to be utilized for this position. I discussed options with the operations manager; and have decided to close the FIMR position and combine it at Woodland Radar (WDLR) 134.2 primary frequency. We need 120.4 Primary and Secondary to return to service before FIMR can be de-combined safely; in my opinion. This puts a heavy workload on WDLR as they are now working both BUR and VNY arrivals during heavy traffic. Traffic Management Unit has added flow to assist in the safe operation of the WDLR/FIMR position combined. The ECS frequencies (be it 120.4; 135.05; 119.85) is completely unreliable and we have no other frequency we can depend on to talk to aircraft.