Parts List - Fender ULTIMATE CHORUS Service Manual

1 second) set up by R139 and C73. This allows time for the circuitry to stabilize, which prevents turn-on
pops and snaps.
The inhibit switches are located within the input jacks. The control voltage through CR55 to U10A locks the
unit in the DRIVE channel mode, muting the NORMAL channel and NORMAL REVERB. At the same time,
the inhibit voltage mutes the DRIVE channel and DRIVE REVERB. AT JFET Q6, the Chorus output has
it's own turn-on delay circuit. If the Chorus button is engaged before power-up, R88 and C49 will provide a
delayed turn-on for the Chorus. Again to prevent pops and snaps.
POWER AMPLIFIERS (The following reference designators apply to the Left amplifier)
U8 (MC1436) is a high-voltage op-amp that provides voltage gain for the power amplifier. CR28 and CR29
act as differential protection diodes that prevent the positive and negative inputs of U8 from becoming more
than 0.6 volts apart. Bootstrap Capacitors C59 and C60 sense the output through R107. This provides
more voltage swing for the opamp with respect to ground.
Diodes' CR30-CR33 (BYV26D) make up the Fixed-Bias circuit for the output transistors. The Bias Diodes
mount through a hole in the transistor heatsink.
temperature of the output transistors. These Diodes were selected because they exhibit a 2mV decrease
in Knee Voltage for every 1 degree (Celsius) increase in temperature. Pin 6 of U8 is at 0Vdc. Therefore
the Bias Diodes provide 2 voltage drops (+/-1.2volts) to the Base of Darlington Transistors Q8 and Q9.
TROUBLESHOOTING TIP: With the circuit board removed, the heatsinking for the output transistors is
greatly reduced. With no signal applied, the Bias/Idle current will cause the output transistors to quickly
overheat. Use a jumper wire to short across the bias diodes. The easiest way is to jumper from the bases
of opposing output transistors. This will turn off the transistors.
Diodes' CR34-CR37 make up a voltage clamp protection circuit. IF the bases of the output transistors
reach 4.5 volts with respect to the output, the diodes will turn on, clamping the bases of the output
transistors. The power amplifiers each provide 63 watts at 5% THD into a single 8 ohm speaker.
QTY PART # DESCRIPTION
1 039246 PCB ASY "ULTIMATE CHORUS" ALL VOLTS
1 031910 BREAKER THERMAL 15A 155/195 DEG F
3 028104 BUTTON PUSH SWITCH BLACK
1 028577 CABLE ASSY REVERB 30"
6 038689 CAP AE AX
4 038690 CAP AE AX
7 026517 CAP AE AX
2 038691 CAP AE AX
2 038692 CAP AE AX
10 025960 CAP AE AX
1 038693 CAP AE AX
4 028471 CAP AE RDL 50V 47uF 20%
2 028474 CAP AE RDL 25V 100uF 20%
1 028479 CAP AE RDL 25V 220iF 20%
2 031756 CAP AE RDL 50V 4700uF
2 038873 CAP CA 100V 22pF 5%
3 038698 CAP CA 100V 47pF 5%
4 038699 CAP CA 100V 100pF 5%
1 039259 CAP CA 100V 220pF 5%
3 038701 CAP CA 50V 470pF 5%
ULTIMATE CHORUS
THEORY OF OPERATION (CONT)

PARTS LIST

PRINTED CIRCUIT BOARD ASSEMBLY
100V .47uF 20%
100V 1uF 20%
50V 2.2uF 20%
50V 4.7uF 20%
35V 10uF 20%
16V 22uF 20%
50V 47uF 20%
This ensures the Diodes will properly track the
REFERENCE DESIGNATION
(STUFFED)
TS1
(@ S1,2,3)
(REVERB CABLE)
C14,16,29,32,38,48
C49,73,80,83
C37,55,56,58,64,65,67
C57,66
C3,4
C5,30,36,42,51,53,61,62,70,71
C78
C59,60,68,69
C88,89
C41
C84,85
C28,82
C35,54,63
C33,40,50,52
C46
C7,15,25