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Author Topic: Help required Dolby Cat.150D Rob J. Buskop Expert Film Handler Posts: 111 From: Rotterdam, the Netherlands Registered: Aug 2005 posted 11-15-2012 08:07 AM                     Have a Cat.150D on my bench that works well, with output on all channels, but the LED on channel 4 does'nt work. Diode measuring through this led is normal. Don't have a schematic but would like to sort this out. Anybody with a schematic out there, or technical suggestion? Thank you for your attention! R.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 11-15-2012 09:25 AM                       As I remember it has a current limiting resistor. I would leave well enough alone as there are some high impedance components you are likely to damage. Dolby stopped publishing schematics years back and in any case that does little to tell you where the part actually sits.  |  IP: Logged Rob J. Buskop Expert Film Handler Posts: 111 From: Rotterdam, the Netherlands Registered: Aug 2005 posted 11-15-2012 11:02 AM                     The basic set-up should be simple like rectifying the audio signal at some stage, or possibly indirectly stimulating a VCA. Should be rather easy to repair when you know the basic circuitry. Anyway, thanks for your response, Sam!  |  IP: Logged Rob J. Buskop Expert Film Handler Posts: 111 From: Rotterdam, the Netherlands Registered: Aug 2005 posted 11-17-2012 08:50 AM                     As it sometimes happens, the cure was relatively simple. Took the boards apart and followed the signal path to the led. Put my tweezers on the current reducer R to check and.... found one end of the resistor had'nt connected in the tin bath manufacturing process. Problem solved.  |  IP: Logged

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