1.0 General Description Diagram 1 provides a simplified block diagram to show major sub systems. Note that the schematic reference designations and pinouts used in this manual refer to the AQ revision of both the main PCB, and schematic. 1.1 Main PC Board Revisions There are 3 major main PC Board revisions. • A-This was the initial release. This board revision will require the most extensive updating of the three. • CA-This version of the board was a 4 layer design. While offering several advantages over the older version (improved R.F. characteristics, smaller size, etc.) it was found to be extremely difficult to service (internal shorts can only be repaired using lifted pins and jumpers).
• AQ-This was the final revision. This revision will of course need the fewest updates, and should be relatively easy to troubleshoot. Diagram 2 is provided in order to assist with board revision identification. 2.0 Power Supply The power supply begins with the 9 Volt A.C., adapter (Alesis P2 [mini plug] or P3 [barrel] types). Input from J1 is R.F. filtered before on/off switch S1. From there it is split for the +12V, -12V, and +5V rails. The +12V rail consists of a voltage doubler (C1, C3, and D2, D3), a 7812 regulator (U8), and a filter capacitor (C6).
The -12V rail is a "mirror" of the +12V rail, consisting of voltage doubler (C2, C4, and D1, D4), a 7912 regulator (U9), and a filter capacitor (C7). The +5V rail consists of a rectifier diode (D5), a filter capacitor (C5), a 7805 regulator (U10), and a multitude of 0.1 µ F bypass capacitors. Note that the raw +10V line used by the microprocessor reset, and the SRAM power supply (when retrofitted), is located at the input to the 7805 regulator. Note that revision AQ (the latest) boards also incorporate several R.F. suppression chokes and current limiting resistors.
These have resulted in a few unique situations that may need to be dealt with (see section 7.16 for details) Diagram 1 HR-16/HR16B Service Manual 1.00 1