Preliminary inspection of the receiver, of course, pointed to noises or crackles characteristic of this age when switching sources, or, for example, switching on the bass and treble controls.

It's time to start by cleaning the potentiometers and all the switches. Clean off old grease and oxidized copper tarnish. First of all, remember that the potentiometers after cleaning should not work very loosely - this is a symptom of the lack of grease, which was and is necessary for proper operation. They have all been desoldered.

Pre-cleaning in an ultrasonic cleaner to dissolve the old grease.

Dismantling the switches and cleaning the contacts.

Grease application - contact protection.

After cleaning the potentiometers and switches, it's time to look at the value of the components of the power board.

Power Supply Board (AWR-101)

Some of the units from this series (I have also encountered such ones) had a C12 capacitor installed on the power supply board: 1000uF 35v ACH-039, which was of course replaced with the Nichicon UPW 2200uf 35v series (very long life). Later it was factory fitted. The power supply board (AWR-101) contains twelve C10 to C16, C18 to C21 and C23 aluminum electrolytic capacitors. All of them were replaced with low-impedance Elna and Nichicon UPW/UPM, FG capacitors.

C10: rated capacitance - 470uF, measured - 365uF

C11: rated capacitance - 470uF, measured - 388uF

C12: rated capacitance - 1000uF, measured - 1120uF - changed to 2200uF

C13: rated capacitance - 1000uF, measured - 1055uF

C14: rated capacity - 47uF, measured - 63uF

C15: rated capacitance - 470uF, measured - 365uF

C16: rated capacitance - 47uF, measured - 60uF

C18: rated capacitance - 47uF, measured - 30uF

C19: rated capacitance - 47uF, measured - 59uF

C20: rated capacitance - 100uF, measured - 121uF

C21: rated capacity - 47uF, measured - 61uF

C23: rated capacitance - 100uF, measured - 88uF

Before:

After:

All transistors on the power supply board have been replaced to improve the stability of its operation. After 45 years of service, replacing them will improve and stabilize the voltages. Below is a list of original and replacement transistors. The four transistors Q1, Q2, Q8 and Q9 are mounted on a heat sink. Old thermal pads were replaced with new ones. The old thermal paste has been cleaned and replaced with new silicone thermal paste.

Q1: NPN, 2SD313 (original), replaced with new Fairchild KSC2073TU

Q2: PNP, 2SB507 (original), replaced by new Fairchild KSA940TU

Q3: NPN, 2SC1384 (original), replaced by new Fairchild KSC2383YTA

Q4: PNP, 2SA720 (original), replaced with new Fairchild KSA1013YBU

Q5: NPN, 2SC1384 (original), replaced with new Fairchild KSC2690AYSTU

Q6: PNP, 2SA720 (original), replaced by new Fairchild KSA1013YBU

Q7: NPN, 2SC1384 (original), replaced by new Fairchild KSC2383YTA

Q8: NPN, 2SD313 (original), replaced by new Fairchild KSC2073TU

Q9: NPN, 2SD313 (original), replaced by new Fairchild KSC2073TU

Q10: NPN, 2SC869 (original), replaced by new Fairchild KSC2383YTA

Protection plate (AWM-062-0)

The security chip on the Pioneer SX-950 has the same design as the Pioneer SX-1010. There are two capacitors (C1, C2) and four aluminum electrolytic capacitors (C3 to C6). Two Sanyo coupling capacitors. I replaced them with Wima polyester foil capacitors. The other aluminum ones were also replaced with low-impedance Nichicons from the UPW and FG series.

I replaced the original 2SC1384 transistor with a new Fairchild KSC2690. The new transistor has the same pins as the original one. I also added a safety fly-back diode (1N4004G) to the circuit to prevent potential damage to the output. A safety diode was soldered between pins 9 (anode, "+") and 10 (cathode, "-"). Of course, all other transistors have also been replaced.

Tone booster board (AWG-039):

The tone amplifier board has two solid tantalum capacitors (C25, C26), eight electrolytic capacitors (C13, C14, C15, C16, C19, C20, C23, C24) and two aluminum capacitors (C21, C22).

The original tantalum capacitors have been replaced with Wima polyester film capacitors. All original low leakage capacitors have been replaced with new Nichicon low leakage capacitors. Finally, two aluminum filter capacitors (C21, C22) were replaced with low-ohm Nichicon FG capacitors.

The two original NPN transistors (Q1 and Q2) are 2SC1312. This transistor becomes very noisy over time. I replaced both original ones with new low-noise Fairchild KSA1845. You have to pay attention to the arrangement of the pins of the new transistor! The original transistor is BCE and the new one is ECB.

Flat amplifier board (AWG-038):

The flat amplifier board has four low leakage capacitors installed in the signal path (C1, C2, C5, C6), four solid tantalum capacitors (C17, C18, C23, C24), two low leakage capacitors (C25, C26), and three aluminum - filtering (C13, C14, C27).

Two capacitors (C1, C2) installed in the input signal path have been replaced with foil polyester WIMA capacitors. The remaining four low leakage electric capacitors and four tantalum capacitors have been replaced with new Nichicon low leakage capacitors. The remaining three aluminum filter capacitors (C13, C14, C27) were replaced with low-ohm Nichicon capacitors.

The two original PNP transistors (Q5 and Q6) installed on this board are 2SA725. The failure of this transistor usually results in a crackling/popping sound. I replaced both with new ones, Fairchild KSA992. Once again, you have to pay attention to the new transistors! The original transistor is BCE and the new one is ECB.

EQ Correction Board (AWF-011):

The original PNP transistors (Q1 and Q2) installed in the first stage are 2SA725. The failure of this transistor usually results in a crackling/popping sound. I replaced both with new ones - Fairchild KSA992. Again, you need to check the pin layout on the new transistors. The original transistor is BCE and the new one is ECB.

The two coupling capacitors (C1, C2) installed in the input signal path are Sanyo. I replaced them with WIMA polyester foil capacitors to improve the signal-to-noise ratio. Two low-tight capacitors (C11, C12) have been replaced with new Nichicon UPW. And the remaining aluminum electrolytic capacitors (C7, C8, C17, C18) were replaced with low-ohm Nichicon UPW capacitors.

  C1: rated capacity - 1uF, measured - 1.5uF

C2: rated capacity - 1uF, measured - 1.4uF

C7: rated capacitance - 330uF, measured - 356uF

C8: rated capacitance - 330uF, measured - 377uF

C11: rated capacitance - 3.3 uF, measured - 4.2 uF

C12: rated capacitance - 3.3 uF, measured - 4.4 uF

C18: rated capacitance - 220uF, measured - 180uF

Receiver lighting:

All original STANLEY bulbs in this fixture have been replaced with new warm white LED bulbs (8V wedge base). Each lamp is inserted into a separate socket and is very easy to replace.

Adjustment of DC voltages and Bias:

At the end of my work, I adjusted the DC voltage and Bias on the power amplifier according to the service manual. Before adjustment, two jumpers were removed and a 5.1 kΩ resistor was connected to the POWER IN jacks.

The DC offset in the left channel is measured between pins 10 and 9. In the right channel, it is measured between pins 25 and 24. The DC offset should be set as close to zero as possible with the trimming resistors VR1 and VR2.

Adjustment of the left channel quiescent currents is measured between pins 12 (+) and 13 (-). On the right channel, it is measured between pins 27 (+) and 28 (-). Bias should be set to ~20mV with trimming resistors VR3 and VR4, which didn't need to be replaced.

Renovation of the front, cleaning of the knobs, installation of a new front glass and renovation of the housing:

The front of the receiver was in impeccable condition, but it needed replacing the glass, which was terribly scratched. The assembly of the new glass shows the very careful silk-screening of the FM scale.

The scratched front also underwent revitalization, thanks to which most of the scratches have disappeared.

After removing the scratches, I went to renovate the housing. I wanted to recreate the same color. I left the veneer in the original because it had no damage (which is very rare after so many years!). I got the color after a slight darkening with Starwax. After a full day, wax polish from the Italian manufacturer Cera Lucidante was used, which deeply nourishes and protects after drying.

Working result below:

The effect of the finished work in its entirety and already at the client's home:

and with a happy owner :)

Thanks for reading the whole thing!

Best regards

RetroHiFi.pl