Doug Fleenor Design RR (Rotor-Router) User Manual
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TROUBLESHOOTING
We hope your DMX512 combine unit never needs service. If it does, the information presented here
may be of assistance.
Access to the inside of the unit is accomplished by removing four top cover screws and removing
the top cover.
There is a 1/2 amp fast blow fuse inside the unit. If the POWER indicator does not illuminate when
the line cord is plugged in, check the fuse.
Board Level Troubleshooting Notes
Power supply. The entire combine unit runs on +5 volts. This is generated by stepping the line
voltage down to 10 volts AC which is rectified by a 1 amp bridge rectifier circuit. A 2200 uF
capacitor filters the rectified AC and a 7805 regulates it down to 5 volts. All the parts used in the
power supply section (except the transformer) are available at most electronic parts stores including
Radio Shack. The transformer is a Signal part number LP 20-300. This is available from Signal
(phone number 516-239-5777) or from Doug Fleenor Design (phone number 805-481-9599).
Microprocessor. The microprocessor circuit uses a PIC18C242. The processor's program is held
internally to the microprocessor, so even if you could find a replacement PIC18C242, it would not
work until programmed. Replacement microprocessors are available from Doug Fleenor Design.
MAX483. The MAX483s are the input and output buffers. The inputs and outputs are protected
against damaging voltages up to 120 volts continuous and 15,000 volt transients. They are unlikely
to fail. If the '483 is not available, a more common "pin compatible" circuit is the SN75176. The
'75176 may be used in an emergency, however it will cause the power supply to run hotter and does
not have the slew-rate-limiting feature of the '483.
6N137. The 6N137 is the optical isolation circuit. Although they are not available at Radio Shack,
the are fairly common and are probably carried by larger electronic supply stores.
HPR100. The HPR100 is a 5 volt in, 5 volt out DC to DC converter. The 5 volts in is converted to
AC, run through an isolation transformer, then converted back to 5 volts DC. Thus the output is the
same voltage as the input, but the two sides are electrically isolated. This, in conjunction with the
6N137 above, enable the isolated DMX512 inputs to function.