Printed Circuit Boards
Automatic Shutdown (ERP Control) PCB
2-9
Audio Muting circuits
(page 1 Zone A3–A6)
Each of the 6 muting transistors requires an isolated current source to turn them on and
prevent crosstalk and distortion when o. Q13–Q19 provide this function and are driven
together by Q20. Q21 and Q22 sense the incoming DC voltage and ensure that muting is
activated whenever the incoming voltage is less than approximately 10V. The MUTE signal
from the Engine PCB further extends the mute time at power up until the sound generator
circuits are initialized and stable.
Automatic Shutdown (ERP Control) PCB
The following function summary descriptions reference the ERP Control PCB, Rev D,
schematic circuit drawing (Chapter 7, page 7-12).
Instruments imported into Europe beginning in 2013 must, by law, automatically shut down
after a period of inactivity. SP5-8 units exported to Europe implement this by means of a
small Automatic Shutdown PCB installed on the rear panel near the DC Power jack. This PCB
will interrupt DC power to the Right Front Panel PCB if the unit fails to send any MIDI data
for more than approximately four hours. As required by the ERP regulation, this function
must be enabled by default from the factory however the user may disable it.
This PCB consists of a timer, a MIDI activity sensor, and a switch transistor. It measures
about 30x50mm and is mounted above the MIDI jacks. Two cables connect to the Right Front
Panel PCB and one to the power switch. The timer is reset when power is rst turned on and
whenever a keystroke or sound program change causes MIDI to be sent. The timer may be
defeated by pressing the Defeat switch so that it pops out.
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