Kurzweil CUP2, Service Manual

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Reference Designations
C100 C88 R107 R118
C56 C89 R108 R119
C62 C90 R109 R120
C73 C91 R110 R36
C74 C99 R111 R37
C84 R101 R112 R39
C85 R102 R113 R41
C86 R105 R114 R59
C87 R106 R117 R68
Table 2-2 DNS components
Function Summary
The CUP2 Audio PCB performs the following functions:
1. Provides reg5V, +15V, and -15V DC power to other boards
2. Mixes the external Line In audio with the Engine PCB audio
3. Headphone ampli  er
4. Frequency response shaping to optimize speaker performance
5. Two-way crossover  ltering to separate woofer and tweeter signals
6. A separate power ampli  er for each of the four speakers
7. Muting during power-up and power-down to prevent loud pops
The following function summary descriptions reference the generic Mark 5/10 Audio PCB,
Rev D Ver 1, schematic circuit drawings (Chapter 7, pages 7-10 through 7-12). Note that a
component value marking of "DNS" means the component is not present in the CUP2
assembly.
Power supply recti  ers,  lters, and regulators
(page 1)
The power transformer has three separate center-tapped secondary windings with voltage
ratings of 14V CT, 36V CT, and 56V CT. These enter through 9-pin J501 and are recti
 ed half-
bridge D2 and full bridges D3 and D1 to produce unreg8VDC, +/-24VDC, and
+/-36VDC respectively. VR1 uses +24V to p15V and VR2 uses -24V regulated for
powering sensitive low-level audio circuits. U1 and surrounding components form a very low
dropout, high current regulator for +5V, which powers all of the digital circuits.
Q1, R5, and R6 sense the error ampli  er output to determine if +5V (which has the highest
current drain) is in regulation. Q1 will be on when the error ampli  er is in its linear region and
regulating successfully.
Printed Circuit Boards
Audio PCB
2- 10