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Contents List
! Circuit description
o
A80/P80
! Technical specifications
! Circuit diagrams
o L943AY
! Transformers
o
L916TX - 115/230VAC toroidal
o
L917TX - 100VAC toroidal
o
L907TX - 100VAC frame
! Exploded view diagram
o
A80
! Mechanical & packing parts list
o A80
o P80
! Circuit board silk screen
o
A80
o
P80
! Circuit board parts list
o
A80/P80 combined
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Circuit description.
Power supply.
The mains input to the unit is supplied at SK200
and is
filtered the Y Caps and locations C200 /C201 and X
cap at location C209, these are in-place to reduce
mains born HF interference and to prevent bridge
rectifier noise from leaving the unit.
The mains select switch at location SW200
works in
conjunction with the dual primaries on the 115/230v
transformers, the switch allows for the units to be used
in territories running a 115v or 230v grid when the
switch is set to the 115v position the primary windings
are connected in parallel.
Fig 1. Fuse value information.
Fuse location. Value.
FS200 T2.5A (20mm)
FS201 T2.5A (20mm)
FS200 (100v) T3.15A (20mm)
FS201 (100v) T3.15A (20mm)
FS202 (s.m standby 9v a.c rms) T500mA (s.m)
FS203 (D.C inline) T2.0A (20mm)
FS204 (D.C inline) T2.0A (20mm)
The standby Transformer TX200 continuously powers
the digital
circuitry (+4.8v(D
)) when power is
connected to the unit, this supply powers the Micro via
a regulating circuit based around regulator REG 201
special mention should be made of fuse FS202 as any
interruption to this supply will render the unit
completely lifeless and as such this circuit should be
checked before inspecting any other areas of the
board.
We will see that the main power transformer TX200
supplies a separate secondary winding for the +15
and
-15v analogue
regulation stages via the two fuses at
board locations FS203 and FS204, the failure of either
of these fuses will cause the op-amps connected to the
regulated rails to swing D.C. The regulator at location
REG 200 regulates the +15 rail and intern supplies the
+5V(A) analogue supply via the reference Zener at
location DZ200
and drive transistor TR200.
The high level power amp A.C supplies arrive at
Con204 as a 4-wire supply this allows us to implement
a dual bridge network circuit with 4 individually
smoothed D.C rails these are labelled as +45(L),
+45(R) and -45(L), -45(R) we pull a -38v rail from this
point to form the VFD cathode bias voltage via R211
Con205 delivers the 3.3 V A.C supply to the main
board and then onto the display VFD via R203 (2R2
f.u).
Fig 2. Supply identification and related components.
Supply Related components
+ 45v L
Left power amp positive rail.
+ 45v R
Right power amp positive rail.
- 45v L
Left power amp negative rail.
- 45v R
Right power amp negative rail.
- 38v VFD
Display cathode rail derived from -45v(R)
+15v (A)
IC 300, 301, 302, 303, 304, 305, 306,
307, 308, 309 also including the input
clamp diodes all within the pre-amp stage.
- 15v (A)
IC 300, 301, 302, 303, 304, 305, 306,
307, 308, 309 also including the input
clamp diodes all within the pre-amp stage.
+ 5v (A)
IC309 volume control
+4.8 (D)
Input trigger stages, signal detect IC700,
delayed off IC703, IC701. Main micro
IC600.Remote pickup, Master reset
IC601, Over current detect-AC detect -
thermal cut-out IC600
Fil 1/Fil 2
3.3v~ filament supply.
Pre-amp.
The A80 Pre-amp has inputs for Phono, Aux, CD, Tuner,
AV, DVD and Tape. All inputs except Phono have a simple
resistor-capacitor 340Khz low pass filter to remove any
unwanted high frequency noise from the input signal/local
area, a pair of diodes on each input connected to the
+15/-15v rails prevent damage to the CMOS input
switching chips at locations IC300 and IC301, if any offset
is seen at the input the switching chips on a given input we
may suspect the failure of one of the input diodes.
Fig 3. Logic status of IC302 and 303 (switching chip).
Low= 0V High=4.8 (Cmos).
Input. A0
(pin 1) A1 (pin 16) A2 (pin 15)
Phono Low Low Low
Aux Low High Low
CD High High Low
Tuner Low Low High
AV High Low High
DVD Low High High
Tape High Low Low
The outputs of IC300 (L) and IC301(R) can be seen on pin
8 as a current signal and such this can not be viewed via
CRO although a 100 ohm resistor inline with the scope
probe may yield some results, from here we drive into line
drive op-amp IC307 (L) and IC308 (R) signal can be seen
at the output pin (1) and travelling into the volume control
chip (IC309) on pins 16 (L) and 9 (R) the output from the
Volume control is driven into IC307 at pin 6 (L) and IC308
pin 6 (R) and seen again on pins 7 on both IC307 and
IC308. After the Con 302 and Con 303 we drive directly
