Kurzweil K2000 - K2000 Audio;Power Board Theory - Part 3

SECTION 5
AUDPWR2.DOC 12/15/92
5.1.2 K2000 AUDIO/POWER BOARD THEORY
SCHEMATIC PAGE 2
5.1.2.1 POWER SUPPLY
Refer to K2061 AUDIO/POWER BOARD schematic, page 2 of 6, for details.
The rear panel and bottom shield are used as a heats ink for the five TO-220 packaged power
semiconductors. For testing in unrestricted free air, just the rear panel is acceptable as a
"short-term" heatsink although it will get hot to the touch. NOTE: TBSTING WITHOUT A BEATSINK IS
NOT ALLOWED AND WILL RESULT IN SHUTDOWN OR DBSTRDC'l'ION OJ!' SOMB OF THE POWER SEMICONDUCTORS IN A
MATTER OF SBCONDS.
The surfaces between the shield plate and the rear panel should be coated with
white thermal heatsink compound for improved heat dissipation.
The rear panel is at analog/chassis ground potential; thus all power semiconductors must use an
insulated mounting. The sketch below (figure 5.1.2.1) details the mounting hardware necessary to
accomplish this. When installing this hardware it is critical that the semiconductor mounting
hole be aligned with the panel mounting hole. If they are not and the screw is forced in, the
screw threads will cut through the wall of the shoulder washer and short-circuit against the
semiconductor's mounting tab.
Figure 5.1.2.1 - Heatsink mounting detail
5.1.2.2 EXTERNAL TRANSFORMER
A separate power transformer converts selected line voltages to 100, 115, or 230 volts.
contains two center-tapped secondaries, 12 and 28 volts. Low voltage AC enters through
1). All voltages in this section will be given for the 115 volt configuration. Figure
below details the external transformer connections .
5.1.2.3
BLfKK/WHT
But"K
8ROWN/WHT
BROWN/'f~L
gROWN
•
~
15V'
lOOV
BLVE
I~Vt
8LVE!WHT.
I'tV t
8LVE
RED
"V t
• Rr=D/WHT.
6V t
Re;'O
Figure 5.1.2.2 - Power transformer wiring
RECTIFIERS AND FILTERS
It
J20 (A-
5.1.2.2
023, 024 (B-1) and C192 (C-l) provide unregulated +20VDC to TP25 (C-l) from which +12Vana,
+5Vana, +5Vref and +8VDC are derived. 021, 022 (B-1) and C190 (C-l) deliver unregulated -20VDC
to TP22 (C-1) to provide -12Vana, -5Vana and -15Vbias. C192 is larger than C190 because of the
potentially greater load from the optional hard disk on the positive supply. C197 and Cl98
prevent low frequency RF rectifier switching noise from feeding back through the line cord.
NOTB: No secondary fuses are provided. Primary fuse in power entry modu~e protects sufficient~y
aqainst current over~oads.
4