Another Sansui 9090DB in the workshop - service and restoration

The Sansui 9090DB includes a 125-watt power amplifier section, direct-reading power meters, an AM/FM analog tuner, Dolby noise reduction circuitry, bass, midrange and treble controls (switchable), two tape loops and a phono preamp.

The delivered amplifier was in tragic, condition. Instead of fuses, wires from a bundle of wires wrapped around carpenter's pegs were used. A protection board with most of the components burned out and an unremarkable relay connected behind to the board by wires. Damaged volume potentiometer which does not turn down to zero. No green LED to indicate the transition from the protect tybu. No main switch, etc. etc. etc.... There were a bunch of these! Especially the Dolby board which always "shows" something (also problems here). 

The amplifier got hit hard, so the full recap and many other components had to be replaced. Filter condensers as well! 

Total drama when it comes to its condition. The work was a lot !!! 

Below is a summary of the full service:

 

1 . Cleaning/washing of the device, disassembly of parts - preparation for further work. Ultrasonic cleaner was used to clean some parts. 

2 DOLBY board - F2655:

Regeneration of the dolby fm selector switch - no signal on the left channel. Replacement of capacitors with Nichicon, Elna Silmic II.  Improvement of the "famous up/down connections". - Adding copper connections to more than 60 holes. The board managed to start up - it works properly. Damage to the board would cause it to bypass, making the receiver lose the TAPE 1 and TAPE 2 function. 

Replaced capacitors:

C-605 ,C-09, C-10, C-11, C-12, C-13, C-14, C-15, C-16, C-19, C-20 ,C-21, C-22, C-29, C-30, C-35, C-38, C-606, C-01, C-02, C-41, C-42, C-608, C-36, C-37

3. microphone amplifier board F2617:

Cleaning and lubricating the microphone volume potentiometer.

Replacement of capacitors:

C-03, C-04, C-06, C-07, C-09, C-10 

 

4. F2624 controller board:

 

Verification and improvement of solder connections. Measurement of resistor values. Replacement of components:

C-01 0.47 50 V EC 2 mm / for low noise 505-MKS20.47/63/5 63 V WIMA.

C-02 0.47 50 V EC 2 mm / for low noise 505-MKS20.47/63/5 63 V WIMA

C-05 470uF/16V/5LS 6.3V , C-06 470uF/16V/5LS 6.3V, C-07 330uF/100V/7.5LS 63V 

C-08 330uF/100V/7.5LS 63V , C-09 100uF/50V/5LS 25V, C-10 100uF/50V/5LS 25V

 

Replacement of DC Offset adjustment resistors and resting currents!

VR1: 4.7 kΩ: on 3296P 5 KΩ, multiturn

VR2: 4.7 kΩ: on 3296P 5 KΩ, multi-turn

VR3: 1 kΩ:, single-turn

VR4: 1 kΩ:, single-turn

Replacement of resistors:

R-33 180 ohm fuse, R-34 180 ohm fuse, R-35 4.7 ohm fuse 

R-36 4.7 ohm fuse, R-39 10 ohm fuse, R-40 10 ohm fuse 

R-41 Fuse 150 ohms, R-42 Fuse 150 ohms, R-43 Fuse 150 ohms 

R-44 Fuse 150 ohms, R-47 Fuse 4.7 ohms, R-48 Fuse 4.7 ohms 

R-49 4.7 ohm fuse, R-50 4.7 ohm fuse, R36: 4.7 ohm 1/4 watt fuse

R37: 3.9 kΩ, 1/2 W, 3.92 kΩ, 1/2 W 

In addition, transistors with matched hfe were replaced:

2SC1400 -> KSC1845F

2SA899 -> KSA1220AY 

2SC1904 ->KSC2690AY

2SC945 -> KSC945C

2SA733 -> KSA733C

5. Power supply board F2656:

Replacement of all fuses, verification of resistors and diodes:

Capacitors:

C-03 1000uF 80V, C-04 470uF 80V, C-05 100uF 80V, C-06 100uF 80V, C-09 220uF 80V, C-10 220uF 63V. 

C-11 10uF 50V, C-14 4.7 uF / B.P 80 V, C-15 4.7 uF / B.P 80 V, C-16 4.7 uF / B.P 80 V 

Resistors:

R-27 4.7 ohms, R-28 4.7 ohms, R-30 Fuse 1 ohm, R-31 Fuse 1 ohm, R-32 Fuse 1 ohm.

6. F2657 relay board:

In the copy, the board was damaged, requiring a major overhaul along with damaged tracks when soldering another relay that did not match the leads. The tracks were pasted and secured. The relay was replaced with the correct one - a new one. The receiver did not receive a green LED indicating that the device was ready - replacing resistor R12 helped. Also replaced the defective setting resistors responsible for the correct operation of the power indicators (adjusted according to the service manual, of course).

C-03 470uF 6.3V, C-04 1uF 50V, C-06 1uF 50V, C-07 1uF 50V, C-08 1uF 50V, C-02 220uF 50V 

C-01 33uF 50V, C-05 47uF / Bi Polar 6.3V 

Rezystory

R-15 201101 100 omów 1 W 

R-16 201101 100 omów 1 W 

R-25 203100 4,7 oma 1/2 W Bezpiecznik 

R-26 203100 4,7 oma 1/2 W Bezpiecznik 

Przekaźnik

RL01 Omron MY3-02-DC24

7. F2544 tone correction board:

I used capacitors from Wima, Nichicon and Elna Silmic II: 

C-09 100uF 6.3V, C-10 100uF 6.3V, C-33 220uF 16v, C-34 220uF 6.3V, C-601 470uF 6.3V, C-602 220uF 50V, C-05 10uF / Audio 25V, C-06 10uF / Audio 25V, C-31 10uF / Audio 25V, C-32 10uF / Audio 25V. 

C-01 1uF / Audio 50 V, C-02 1uF / Audio 50V, C-27 2.2 uF / Audio 50 V, C-28 2.2 uF / Audio 50 V 

I also replaced two notoriously noisy transistors C1313 with low-noise onsemi - KSC1845

8 F2653 selector board:

The input selector was disassembled and cleaned.

Replaced capacitors:

C-602 1uF / Audio 50V, C-19 2.2 uF / Audio 50 V, C-20 2.2 uF / Audio 50 V, C-11 220uF 6.3V, C-12 220uF 6.3V, C-07 470uF 50V, C-08 470uF 50V. 

9. Final power transistors:

All transistors have been verified - they work properly. In addition, the mica pads were replaced with new ones and new thermal conductive paste was applied. The heat sink was also cleaned and lubricated with new thermal conductive paste.

10. RF power supply section board F-2619:

Replaced capacitors:

C-01 100uF 35v, C-02 220uF 16v, C-03 10uF 25v, C-04 470uF 10v, C-05 470uF 16v 

11. AM/FM tuner board F-2549:

The tuner board did not indicate any problems, the tuner was tuned and works very well. 

12. filtering capacitors were replaced with - Kemet 13 000 uf 100 V with high ripple current. I also used a new 4.7 k leakage resistor: ERG-3SJ472A

13. individual capacitors on the switch boards were also replaced. 

14. the voltage selector was also cleaned and I corrected the connections. 

15. the amplifier switch was taken apart and cleaned. In addition, I made a new component for switching on the amplifier (it was supplied without).

16. the amplifier did not have one knob of the microphone volume potentiometer - I fixed a very similar one made of solid aluminum. 

17. the front of the amplifier, as you can see in the photos, had pitting on the silver brushed frame - they were removed. In addition, I repainted the frame to remove the damage - matte black. 

18 The knobs and aluminum switches were washed and polished. The plastic knob brackets were glued in. 

19.All potentiometers were taken apart and cleaned, along with the switches. 

20. I added new feet to the base - they were missing. 

21. lighting was replaced with new ones.

22. Each selector was taken apart and cleaned.

23. the Dolby IC signal (NE545B) was adjusted. 

24. DC offset and resting current (Bias) adjustments were made. After a few days of operation of the amplifier, I verified again. Everything according to the service manual. 

25. The glass and the front of the amplifier were polished. 

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