Fig 4. Suggested blanket replacement parts for
power amp failures.
Location Description
Model
Part
no.
TR413 Output
driver
+ SAP15NY
4CSAP15N
TR415 Output
driver
- SAP15PY
4CSAP15P
TR410
Pre
FMMT 497
4AFMMT497
TR412
Pre
ZDT 6758
4AZDT6758
TR414
Predriver -
ZDT 758
4AZDT758
TR405
Predriver -
FMMT 597
4AFMMT597
TR401
Current mirror PNP
BC859B
4A859
TR402
Current mirror PNP
FMMT 597
4AFMMT597
TR411
Current mirror NPN
FMMT 497
4AFMMT497
TR417
Current mirror NPN
BC849B
4A849B
TR412
Driver bias +
ZDT 6758
4AZDT758
Fig 4a. SAP NY/PY output driver information
.
SAP 15NY SAP 15PY
S-E = 0.22 ohm.
Under output driver failure
conditions the
0.22
internal emitter
resistor will usually go open, the resistor should be measured between
pins S and E.
Micro control/protection and display.
The micro is tasked with providing an instantaneous safe
operating area for both the amplifier and loudspeaker by
monitoring the below areas.
o
D.C
at both left and right channel outputs.
o
Over current
within either power amp stage.
o
Over temp
detection for both power amp stages.
o
A.C present
detection.
Please see fig 5.
For voltage readings with regards to the protection
operations.
Within the A80 integrated amplifier these tasks are
performed by the H8 type micro at circuit location IC602,
within the P80 power amp version the tasks are performed
by the PIC micro at location IC603, the protection lines are
“daisy chained” to both micros regardless of witch one is
fitted.
To operate both micros require a constant stable supply
voltage, this is derived from the
+4.8v(D)
rail from
transformer TX200 and via regulator REG201 this supply
should be constant at anytime mains appears at the
amplifier power input.
Please note: This supply is protected from over-current
and over-voltage operation by the surface mount fuse at
location
FS202
T500mA and as such if the Amplifier fails
to power up this supply should be checked before making
any further investigations.
We also need to see a
4.00
Mhz
clock at crystal location
X600
.
The micro interfaces with the pre-amp stage input
selection
(see Fig 3)
and the volume control level
adjustment we also drive the VFD via the display
drive/keyboard scan micro at location IC800.
IC602 receives Keyboard scan data and RC5 from the
remote pick-up diode at location RX800. The
master
power on
reset
can be found on the display board and
switches
HI
(4.8v) after mains in.
Fig 5. Working status of protection lines and fault
status
.
Low =0v High = 4.8 (Cmos).
Location Fault Line
Output pin Working
IC 601A
AC present
2
High
IC 600A
Over current
3
Low
IC 600B
Therm prot (L)
6
High
IC 600D
Therm prot (R)
11
High
IC 600C
Therm prot main
8
Low
R634
D.C prot (L)
N/A
Low (D.C)
R635
D.C prot (R)
N/A
Low (D.C)
R663
D.C prot combined
N/A
Low
