Alesis ADAT BRC Service Manual page 17

During the course of development of the BRC, Alesis has found two types of symptoms which
indicate specific problems. These are listed below:
1. Basic functions are not working properly: In this scenario, the first things that should be
checked are the voltage of the battery and the voltage at U8, pin 32. Check both of these voltages
with power off. If the RAM chip U8 isn't supplied with enough voltage when the unit off, then
the BRC could lose some of the data stored in RAM relating to the basic operating functions.
This problem would also manifest itself as losing memory, or parts of memory, when the unit is
powered off.
2. ADATs improperly ID: This would normally manifest itself in two ways: either the ADATs ID
themselves with incorrect ID numbers, or the ADATs constantly re-ID themselves. Both of these
conditions indicate that the ADATs are having problems locking onto the 48 KHZ sync clock
signal coming from the BRC. Whenever this scenario occurs, check the four areas listed below
for potential problems.
1. VCO: This is the clock that the 48 KHZ clock is derived from. From hardware mods
described in Appendix B, C57 has been added to the Revision 1 BRC Main PCB.
Because of this modification, the 5V DC leg of this newly installed cap is in close
proximity to pin 13 of U18, which is the input to one of the output inverters for the
VCO. Excess solder or improperly cut leads could short this pin to 5V, effectively
killing the VCO and the 48 KHZ line as well. Likewise, if C57 is improperly
soldered, it could come loose and make temporary contact with pin 13 of U18, which
will result in distortion of the VCO. Finally, if C57 is bent over U18, it could also
cause distortion of the output of the VCO. If any of the items mentioned above appear
on the Main PCB in question, re-solder C57 in accordance with Appendix B, clean
away any excess solder, visually inspect the C57 lead proximity to U18, and orient
C57 away from U18. This modification has been incorporated onto the new Revision
2 BRC Main PCB layout.
2. 48 KHZ output to ADAT: This problem deals with the 48 KHz output at pin 7 of
connector J10. R84 is 48 KHz and R83 is its 5V reference to the ADAT's opto-
isolator circuit (see section 2.3.3). With an ADAT connected, check for a slight
voltage drop across R83, and check R84 for the proper signal. Verify that both
resistors are properly inserted and soldered on the board. Also, verify that there isn't
continuity between the resistors.
3. DB9 output connector J10: Check for improper connections, pins not soldered,
damage to the connector, and the like.
4. Cable between BRC and first ADAT: If this isn't an Alesis approved cable (see
section 1.4), problems could result. Alesis Product Support should have verified with
the customer the type of cable being used prior to issuing the Repair Authorization
(RA), and therefore it is unlikely that the cable is the problem. However, if this is in
question, contact Alesis Product Support.
Finally, there is the problem of BRCs intermittently resetting. The symptoms of this problem are
similar to those relating to BRCs improperly IDing. However, in this case, the BRC will continue to
cycle power every so often. That is, the BRC LCD back light will dim momentarily. If the LCD display
does not dim, then the problem is probably related to one of the above items.
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