PRINCETON 112 PLUS
p/n 022-6704-010 (120V)
SERVICE MANUAL
CONTENTS:
Notices
Specifications
Therory of operation
Parts lists:
PCB Assembly
Chassis assembly
Footswitch assembly
Cabinet assembly
Miscellaneous
Schematics
Service diagram
Fender Musical Instruments Corp.7975 North Hayden Road Scottsdale, AZ 85258
PRINCETON 112 PLUS
(This is the model name for warranty claims)
APRIL 1995 REV A
IMPORTANT NOTICE:
The information contained herein is CONFIDENTIAL and PROPRIETARY to Fender Musical Instruments Corp. It is disclosed solely for use by qualified technicians for purposes of equipment maintenance and service. It is not to be disclosed to others without the expressed permission of Fender Musical Instruments Co. All specifications subject to change without notice.
For warranty repair service, only Fender specified part numbers are to be used. It is recommended they also be used for post-warranty maintenance and repair.
Parts marked with an asterick (*) indicate the required use of that specific part. This is necessary for RELIABILITY and SAFETY requirements. DO NOT USE A SUBSTITUTE!
A coded naming convention is used in the description of certain parts. The codes and what they mean are as follows:
CAPACITOR CODES |
HARDWARE CODES |
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CAP AE |
= |
Aluminum Electrolytic |
BLX |
= |
Black Oxide |
CAP CA |
= |
Ceramic Axial |
CR |
= |
Chrome Plated |
CAP CD |
= |
Ceramic Disk |
HWH |
= |
Hex Washer Head |
CAP MPF |
= |
Metalized Polyester Film |
M |
= |
Machine Screw |
CAP MY |
= |
Mylar |
NI |
= |
Nickel Plated |
CAP PFF |
= |
Polyester Film/Foil |
OHP |
= |
Oval Head Phillips |
RESISTOR CODES |
PB |
= |
Particle Board |
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PHP |
= |
Pan Head Phillips |
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PHPS |
= Pan Head Phillips Sems |
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RES CC |
= |
Carbon Comp |
SMA |
= Sheet Metal "A" Point |
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RES CF |
= |
Carbon Film |
SMB |
= Sheet Metal "B" Point |
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RES FP |
= |
Flame Proof |
SS |
= |
Stainless Steel |
RES MF |
= |
Metal Film |
TF |
= |
Thread Forming |
RES WW |
= |
Wire Wound |
ZI |
= |
Zinc Plated |
1
SPECIFICATIONS
Part Number: |
022-6704-010 (120V) |
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022-6734-010 (240V Australia) |
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022-6744-010 (230V UK) |
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022-6764-010 (230V) |
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022-6774-010 (100V) |
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Input impedance: |
Greater than 1M Ohm |
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Nominal input level: |
100mV |
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Power output: |
63 Watts R.M.S. @ 5% T.H.D |
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Rated load impedance: |
8 Ohms |
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Effects loop: |
Nominal level |
-10 dBv |
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Output impedance 1k Ohm |
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Input impedance |
16k Ohms |
Dimensions: |
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Width: |
18-5/8 inches |
(47.3 cm) |
Height: |
16-1/2 inches |
(41.9 cm) |
Depth: |
9 inches |
(22.9 cm) |
Weight: |
28 lbs. |
(12.7 kg) |
THEORY OF OPERATION
PREAMP
Input jack J1 contains the switching circuit for the inhibit function of the 4053 CMOS switch
(U7). Without a plug inserted into J1 -8Vdc is available to pin 6 of U7A. This inhibits the CMOS switch from functioning, effectively muting the preamp. When the input plug is inserted into J1,
+8Vdc becomes available at the inhibit line allowing the CMOS switch to function. TROUBLESHOOTING TIP: When the channel switching circuit does not operate, first check that the inhibit voltage toggles properly. In some cases a faulty CMOS switch can load down the inhibit line. Desolder pin 6 (of U7) and check that the voltage toggles between -8Vdc to +8Vdc.
If so, the CMOS switch may need to be replaced.
The first stage (U1A) sets up the initial response of the amplifier. It provides a second order high pass filter with a 3dB down point at 60 Hz, and a gain of about 3.5. The output of U1A splits to feed the clean and overdrive channels. For the clean channel, the signal feeds the treble and bass controls, which provide boost and cut respectively. The signal then flows to the Auto-pad circuit (U1B). It provides excellent headroom and low noise. At upper volume control settings, it also rolls off low frequencies.
The signal split from U1A feeds the overdrive channel through a special tone shaping circuit located just prior to U2A. This circuit is a third order bandpass filter with a peak boost at 2.2kHz. It provides the optimum frequency response for the distortion circuit that follows. U2A provides the variable gain adjustment that drives the distortion circuit. It also acts as a bandpass filter with 3dB down points at 90Hz and 4kHz. U2B is the distortion circuit. LD1 and LD2 provide diode distortion.
The Contour control adjusts the overall tone quality of the overdrive channel by emphasizing or notching the mid range frequencies. In the fully CCW position the response is fairly flat up to about 2kHz, where a gentle roll-off occurs. In the fully CW position, the circuit provides a -20db notch at about 1kHz. The signal then feeds the overdrive volume control and then to the treble and bass controls.
U3B sums the clean and overdrive channels through CMOS switches U7B and U7C. The output from U3B feeds the reverb drive circuit (U4B) and summing amp U3A. U4A is the reverb sensing circuit. The output of U4A drives the reverb volume control and then feeds through U7A, which sums the reverb with the dry signal at U3A. The output of U3A drives the preamp out jack, is normalled through the power amp in jack, and feeds the power amp input.
2
THEORY OF OPERATION CONT.
CHANNEL AND REVERB SWITCHING
The A.C. voltage from the power transformer secondary is tapped off through dropping resistor
R73, and presented to the footswitch jack (Approx 20 V R.M.S.). By rectifying the positive or negative side of the waveform, we create a D.C. control voltage that is sensed by comparators U6A and U6B. Diode's CR18 and CR21 set up the reference voltages for the comparators.
Therefore the control voltage must toggle above and below the reference voltage to cause the output of the comparator to toggle between +15Vdc and -15Vdc. The comparator output controls the state of the CMOS switches and the indicator LEDs. Without the footswitch connected to the footswitch jack, CR15 rectifies the negative half of the waveform. U6B senses the DC control voltage, and provides -15vdc to U7A, allowing the reverb output to function.
POWER AMPLIFIER
U5 is a high voltage op-amp that provides voltage gain for the power amplifier. CR3 and CR4 act as differential protection diodes that prevent the positive and negative inputs of U5 from becoming more than 0.6 volts apart. Bootstrap Capacitors C38 and C39 sense the output through R60. This provides more voltage swing for the opamp with respect to ground.
Diodes' CR5 - CR8 (BYV26D) make up the Fixed Bias circuit for the output transistors. The Bias Diodes mount through a hole in the transistor heatsink. This insures the Diodes will properly track the 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 U5 is at 0 Vdc. Therefore the Bias Diodes provide 2 voltage drops (+/-1.2volts) to the Base of Darlington Transistors Q1 and Q2.
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' CR9 - CR12 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 output signal feeds through the Headphone jack circuit, before driving the speaker. With headphones connected to the Headphone Jack, the speaker is muted and a new feedback path is created through R78.
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PARTS LIST |
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PRINTED CIRCUIT BOARD ASSEMBLY |
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QTY |
PART # |
DESCRIPTION |
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REFERENCE DESIGNATION |
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1 |
048523001 |
PCB ASSY PRINCETON 112 PLUS |
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1 |
028104 |
BUTTON PUSH SWITCH BLACK |
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(@ S1 DRIVE SELECT) |
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1 |
028577 |
CABLE ASSY REVERB 30 |
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(@ P1-4) |
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4 |
038689 |
CAP AE AX |
.47µF |
100V |
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C15,16,28,34 |
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6 |
025960 |
CAP AE AX |
22µF |
16V |
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C9,10,25,32,40,41 |
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1 |
038690 |
CAP AE AX |
1.0µF |
100V |
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C53 |
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5 |
026517 |
CAP AE AX |
2.2µF |
50V |
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C7,35,37,42,43 |
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1 |
038691 |
CAP AE AX |
4.7µF |
50V |
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C36 |
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4 |
028471 |
CAP AE RDL |
47µF |
50V |
20% |
C38,39,51,52 |
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2 |
041048 |
CAP AE RDL |
2200µF |
50V |
20% |
C47,48 |
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2 |
038703 |
CAP CA |
.1µF |
50V |
5% |
C49,50 |
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1 |
038873 |
CAP CA |
22pF |
100V |
5% |
C31 |
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1 |
038698 |
CAP CA |
47pF |
100V |
5% |
C33 |
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3 |
038699 |
CAP CA |
100pF |
100V |
5% |
C6,24,27 |
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1 |
038701 |
CAP CA |
470pF |
50V |
5% |
C14 |
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1 |
039262 |
CAP CA |
680pF |
100V |
5% |
C17 |
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1 |
039263 |
CAP CA |
1000pF |
100V |
5% |
C3 |
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1 |
039264 |
CAP CA |
1500pF |
100V |
5% |
C22 |
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2 |
039265 |
CAP CA |
2200pF |
100V |
5% |
C8,26 |
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1 |
039266 |
CAP CA |
3300pF |
100V |
5% |
C21 |
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2 |
039268 |
CAP CA |
4700pF |
50V |
5% |
C1,2 |
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1 |
027281 |
CAP MPF |
.22µF |
63V |
10% |
C5 |
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2 |
027286 |
CAP MPF |
.47µF |
63V |
10% |
C4,44 |
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1 |
036234 |
CAP PFF RDL |
.015µF |
100V |
10% |
C29 |
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1 |
033590 |
CAP PFF RDL |
.022µF |
100V |
10% |
C20 |
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6 |
033591 |
CAP PFF RDL |
.033µF |
100V |
10% |
C11-13,30,45,46 |
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3 |
033592 |
CAP PFF RDL |
.047µF |
100V |
10% |
C18,19,23 |
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2 |
037324 |
CONTROL 100K 30C SNAP IN |
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R23,32 |
(GAIN,DRIVE CH-TREBLE) |
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2 |
037323 |
CONTROL 50K 15A SNAP IN |
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R8,9 |
(CLEAN CH TREBLE,BASS) |
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2 |
034719 |
CONTROL 50KB SNAP IN |
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R30,44 |
(CONTOUR,REVERB) |
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2 |
038658 |
CONTROL RTRY 50K 30C |
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R16,31 |
(CLEAN/DRIVE VOLUME) |
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1 |
040552 |
CONTROL 250K 30C |
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R37 |
(DRIVE CHANNEL BASS) |
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2 |
064089 |
DIODE 1N4003 200PRV |
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CR13,14 |
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13 |
006260 |
DIODE 1N4448 75PRV |
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CR1-4,9,12,15-21 |
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4 |
020534 |
DIODE 1N5402 RECTIFIER 200PRV C&F |
CR22-25 |
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4 |
028776 * |
DIODE BIAS BYV26D LEAD FORMED |
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CR5-8 |
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2 |
027329 |
DIODE ZEN 1N5228B 3.9V 5% |
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CR10,11 |
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2 |
028119 |
DIODE ZEN 1N5353B 16V 5W 5% |
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CR26,27 |
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2 |
026000 |
FSTN TAB MALE PCB MT .187x.032 |
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CP11,12 |
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10 |
025802 |
FSTN TAB MALE .250x.032 PCB MT |
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CP1-10 |
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2 |
025996 |
FUSE CLIP PCB .250 & 5MM FUSE |
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(@ XF1) |
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1 |
048827 |
FUSE QA 1-1/4x1/4 250V 2AMP |
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F1(100V/120V ONLY) |
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3
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