Sansui 9090DB is a beautiful and powerful model of this brand - output power: 125 watts per channel at 8 Ω. It is an "export" model with the possibility of 4 different input voltages (100/120/220/240V). It was the 1966th unit off assembly line #81 in March 1977. The receiver has undergone a full service with renovation described below:

First, let's see how it arrived:

As you can see - the equipment is already in the wrong hands...

Creaking potentiometers (I'm not talking about the amount of "cleaning agent" escaping), slamming switches (greasy here too...), something hums, etc etc...

At the very beginning, it must be remembered that sansui likes to make mistakes in its schemes, also in screen printing, which also happen in Pioneers. Therefore, photographic documentation before the start is very important here.

In addition, the paths of each board are very delicate, and you really have to be careful not to tear them off when soldering new components.

F2656 power section:

The electrolytes were replaced with high-temperature (105C) low-impedance Nichicon UPW and ELNA Bipolar capacitors.

C-03 1000uF 80V EC 12mm - Nichicon 1000uF 100v

C-04 470uF 80V EC 10mm - Nichicon 470uF 100v

C-05 100uF 80V EC 7mm - Nichicon 100uF 100v

C-06 100uF 80V EC 7mm - Nichicon 100uF 100v

C-09 220uF 80V EC 7mm - Nichicon 220uF 100v

C-10 220uF 63V EC 7mm - Nichicon 220uF 100v

C-11 10uF 50V EC 3mm -Nichicon 10uF 100v

C-14 4.7uF / B.P 80V E.C 4mm -ELNA 4.7uF 100v

C-15 4.7uF / B.P 80V E.C 4mm - ELNA 4.7uF 100v

C-16 4.7uF / B.P 80V E.C. 4mm - ELNA 4.7uF 100v

Additionally, the resistors R30,31,32 were replaced with metal-oxide ones:

R-30 1 ohm R. 500mW (1/2W) + 200C

R-31 1 ohm R. 500mW (1/2W) + 200C

R-32 1 ohm R. 500mW (1/2W) + 200C

BEFORE:

Kondesatory bipolarne wskazywały bardzo duże wartości po za tolerancją, również zostały wymienione na Elna. 

Gniazda bezpieczników oraz pozostałe styki również zostały wyczyszczone. 

PO: 

Power protection board F2657:

All electrolytes have been replaced with low-ohm UPW capacitors. The films have been replaced with high-quality WIMA polypropylene film

  C-03 470uF 25V

C-04 1uF 63v

C-06 1uF 63v

C-07 1uF 63v

C-08 1uF 63v

C-02 220uF 63v

C-01 33uF 100v

C-05 47uF 6.3V

Resistors:

R-15 201101 100 ohms 1W

R-16 201101 100 ohms 1W

R-25 203100 4.7 ohms 1/2 W Fused

R-26 203100 4.7 ohms 1/2 W Fused

New Relay:

RL01 Omron MY3-02-DC24

The fuse holder also needs cleaning! In addition, after the work was completed, it was necessary to replace the diode and two transistors.

The new relay is identical and generally available. That's why it's worth replacing. You can also disassemble and clean the contacts that look like this:

However, replacement is recommended.

F2655 Dolby Board NO:

The Dolby disc of this model is a problem for many service technicians. I followed the advice here to clean all the switches (wafers), tin the rivets and even reconstruct them. All buttons cleared, dolby and input selector cleared. Particular attention was paid to the Dolby switch and the standard problem with cold solders or connecting the lower tracks to the upper ones with tin.

This is what a defective Dolby board looks like (sansui 9090DB):

Broken top/bottom joints.

100% of the solders on the dolby board have been reapplied. In addition, each connection of the up/down paths received a permanent copper connection, eliminating later problems with no sound, where Dolby bypass is used, which results in the loss of TAPE 1 and TAPE 2.

Po serwisie:

The electrolytic capacitors were replaced with Nichicon FG and UPW series.

C-605 100uF 25v

C-09 10uF 63v

C-10 10UF 63V

C-11 10UF 63V

C-12 10UF 63V

C-13 10UF 63v

C-16 10UF 16V

C-15 10UF 63V

C-16 10UF 63V

C-11 10UF 63V

C-20 10UF 63v

C-22 10UF 63V

C-29 10UF 63V

C-30 10UF 63V

C-35 10UF 63V

C-606 100UF 25V

C-01 47UF 35v

C-02 47Uf 63v

C-42 1uF 63v

C-608 1uF 63v

C-36 10uF 63v

C-37 10uF 63v

The wafers of the dolby switch have also been cleaned. Be careful during disassembly and always take photos of the correct positioning!

F2624 driver board:

Very often he receives information that the receiver does not come out of protection. The relay does not turn on. Mostly this is due to the 180ohm resistor which was also replaced in this case. In addition, it is worth mentioning the adjustable resistors (in this model I used BOURNS), responsible for the DC offset and Bias. In the European version they are 1kohm, in some you can get 100ohm (it's worth remembering - there are two types of these boards).

Individual transistors should be checked and replaced in pairs.

After replacing the most important elements:

After soldering, the whole thing is cleaned and protected with PCB varnish

Capacitors:

C-01 0.47 63v

C-02 0.47 63v

C-05 470uF/35v

C-06 470uF/35v

C-07 330uF/100V

C-08 330uF/100v

C-09 100uF/63v

C-10 100uF/50V

VR1: 4.7k ohms

VR2: 4.7k ohms

VR3: 1k ohms

VR4: 1k ohms

diodes

D-05 1N4148 serial Fairchild 2 X 1N4148 D-06 340120 VD1212 2 X 512-1N4148 serial ZD-01 3160 -24R 512-1N5252B FAIRCHILD 1N5252B ZD-02 316070 EQA01-24R

Resistors:

R-33 180 ohm fuse

R-34 180 ohm fuse

R-35 4.7 ohm fuse

R-39 Fuse 10 ohms

R-40 Fuse 10 ohm

R-41 150 ohms

R-42 150 ohms

R-43 150 ohms

R-44 150 ohms

R-48 4.7 ohms

R-49 4.7 ohms

R-50 4.7 ohms

R37: 3.9k ohm 1/2W

F2544 preamplifier:

All potentiometers and switches disassembled and cleaned. The plate was washed and secured.

C-09 100uF 25v

C-10 100uF 25v

C-33 220uF 50V

C-601 470UF 25V

C-602 220UF 63v

C-05 10uf / Audio 63v

C-31 10uF / Audio 63v

C-32 10uF / Audio 63v

C-01 1uF / Audio 63v

C-27 2.2uF / Audio 63v

C-28 2.2uF / Audio 63v

The whole thing is cleaned and protected with a layer of PCB varnish

Cleaning potentiometers and switches:

I will not describe the photos below, they concern a very thorough removal of heavy dirt causing the loss of one channel or noise when moving the potentiometer. 

Obudowa: