The Sansui 990 is the black faced European version of the 9090 receiver released from 1975-1977 as a bigger brother to the 8080 series and latter larger, complimentary output 9090DB. The 9090 is far more reliable in operation than the 9090DB due to earlier production shortcomings of the Dolby assembly.
Power Supply F2546
The regulated supply consists of a single full-wave rectifier for the +36Vdc supply and a full-wave bridge rectifier array for the -/+B rails. The F2546 uses a card-slot header for the F2463 driver assembly.
The full-wave common cathode device was replaced with a state-of-the-art MUR TO-220 type HexFred rectifier and bypass capacitor replaced with a polypropylene Nichicon film capacitor. The TO-220 regulator was replaced with a modern, robust KSC Fairchild type TO-220 with new synthetic Wakefield compound. Small signal devices were replaced with modern, TO92L with better dissipation, Fairchild devices.
The electrolytic capacitors were replaced with a high temp (105C), low impedance PW Nichicon with an increase in DC coupling values for better noise reduction and increase in operating voltages. New VP Bipolar Nichicons were installed under the PCB foil at the driver header mount.
BEFORE
AFTER
-/+B Rail & Reg Vdc Confirmation
Protection F2547
The protection stage detects any DC deviation, load overload and thermal run-off protections. This PCB has several common resistor failures over the life of the unit originally. The 990/9090 uses a LED indicator display common with Sansui’s. The meter calibration points are located on this assembly.
All new ultra-fast, soft recovery Vishay axial diodes installed and Omron relay contacts addressed. All small signal devices were replaced with modern, TO92L with better dissipation, Fairchild devices. Meter adjustments were replaced with seal, precision Bourns potentiometers. New 1/2Watt resistors installed.
All electrolytic capacitors were replaced with a low impedance Nichicon PW type with an increase in operating voltages. Mylar films were replaced with a high grade WIMA polypropylene film capacitors.
BEFORE
AFTER
Drivers F2463
This is where the DB and non DB differ in design with the 9090 employing a quasi-complimentary output stage and differential input. Some idiot had done one of the sloppiest repairs jobs I’ve ever seen requiring extensive re-work and fine repair traces on this assembly.
All new small signal differential pairs were matched and installed with modern, low noise Fairchild TO92 devices. Pre-Drivers, Drivers and thermal Bias transistors were all updated with modern, robust TO126 and TO-220 Fairchild/Onsemi devices with synthetic wakefield compound where needed applied. Varistors and diodes were replaced with modern, general 4148 type axial Vishay diodes.
Differential Mapping
All electrolytic capacitors were replaced with low impedance PW and VP Bipolar Nichicons with an increase in operating voltages. Input .47 and mylar films were replaced with high grade WIMA polypropylene film capacitors. New sealed, precision Bourns potentiometers installed.
BEFORE
AFTER
Bias Confirmation (50mA)
Phono (RIAA EQ) F2541
The front end stage of the 9090 Phono revolves around two monolithic BA312 7SIP IC’s.
Input electrolytic capacitors were replaced with audio grade MUSE BP Nichicons and remaining include low impedance PW Nichicons, with an increase in operating voltages. 1MFD and certain mylar films were replaced with a high grade WIMA polypropylene film capacitors.
BEFORE
AFTER
RIAA Curve Response
Tone (Pre) F2544 & F2543 Mic Amp
Similar to the phono stage the front end of the 9090 uses a 7SIP monolithic pair of BA312 IC’s and NPN SE output stage. The MicAmp assembly as well employs thes BA312 IC.
Input/Output electrolytic capacitors were replaced with audio grade MUSE BP, KT/KA Nichicons and remaining include low impedance PW Nichicons, with an increase in operating voltages. 1MFD values replaced with a high grade WIMA polypropylene film capacitors. Small signal devices were replaced with a low noise TO92 Fairchild devices. Similarly approached to the F2543 Mic Amp rebuild.
BEFORE
AFTER
RF Front End W/ F2550 & Regulated Supply F2431
The front end has a dedicated regulators, multi voltage supply. This PCB tends to dissipate significant heat from the regulator and wire-wound resistors. The regulator was replaced with a robust, modern TO-220 Fairchild device with new synthetic wakefield compound and new ultra-fast, soft recovery diode. New electrolytic capacitors installed with low impedance PW Nichicons with a increase in operating voltages.
BEFORE
AFTER
The RF Front End assembly had all electrolytic and tantalum capacitors replaced with a low impedance Nichicon PW type with increases in operating voltages.
The F2550 Noise Cancelling/MultiPath module was removed and electrolytic capacitors replaced with low impedance PW Nichicons and high grade WIMA polypropylene film capacitors including mylar film. A new sealed, precision Bourns potentiometer installed.
BEFORE
AFTER
Meters
The weak wheat lamp type meters often fail or mismatch. These were upgraded with modern cool white 3.5Vf LED’s and a new dropping resistor value for a positive color match and longer life. Remaining Fuse type lamps were all upgraded with multi-SMD LED’ type.
AUDIO NOTIZEN
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