Is it possible to post an image of the schematic you have of the slide/detector circuit?
One other option, can you disconnect the detectors and see if the fuse would still blow? Keeping in mind that you are not using the LP or napping... Just something to try.
I myself would avoid the snake pit... you did have an appointment for an electrical problem and they still have no one to help, wasting yer time.
Stay cool
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