also if the gap is large (think JD crane exit opto) then only the correct spec will work, the Jcar stuff is fine for trough...you can actually verify this very quickly by using a digital camera (phone!) and "see" the IR leds output brightness,etc sometimes they need slight 'misadjustment' if you know what i mean (off centre focus)
i just noticed its the ball "lock" trough trouble with, double check connectors for good IDC condition.
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