we bought many ultra zone ZMX2600 through TEM from Italy now we have a problem with your product not working when it was started it's glow for 2mn after that the power gone please advise what we can do

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We bought from your compagny this divise ULTRA ZONE ZMX2600  unfortunately last day it was stopped no output program was radiated  when i reach the transmitter site i found the said product off  i tested it it sglow for 2mn after that is shutdown please advise what we can do i trace the fault ifound that the -15v is not fixed and going to zero  we remove the connections inside the problem remain the problem ia the frontal board