ALESIS HR-16 - Manual (Page 15)

HR-16/HR16B Service Manual 1.00 9
7.0 Updates and Corrections
7.1 New SRAM Supply Circuit
• All Revisions.
The new SRAM supply circuit (See diagram
7) supplies a solid 5V to the SRAM, preventing
input data from being higher in amplitude than
the supply voltage, which can cause data
corruption. First, remove the original diode (D8),
then install the new circuit. Diagram 8 shows the
location to install the circuit in Revision A & CA
PC boards, while diagram 6 shows the location
for revision AQ PC boards. The installation of
this circuit is highly recommended, and is
absolutely necessary if a 58257 SRAM is in the
unit. This is because '257s are much more
sensitive to supply voltage the older '256
SRAMs.
7.2 Glass Zener (D15)
• Revisions A & CA.
For a short time, glass package 1N5231B
zener diodes were used instead of the more
familiar metal package. These were found to be
unreliable, and should be replaced with metal
package zeners.
Diagram 6
2N4401
Diagram 7
Diagram 8