Pioneer SX-3800 Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Pioneer

Model: SX-3800

SN: BC3622209S

Today I'm showcasing a Pioneer SX-3800 vintage receiver that came in for restoration. The SX-3800 was manufactured from 1980 to 1981. At this time, technology was slowly moving from analog to digital. The SX-3800 has an analog tuning dial along with a blue fluorescent display. The quartz-locked FM tuner provides excellent selectivity, low distortion, and stable reception. The reception frequency display indicates the frequency of the broadcasting station in five digits. It helps to tune quickly in a station.  A logarithmic power meter allows a power output level display from 0.01 watts up to 80 watts without range selection on a bar graph display. A non-switching amplifier system employed in SX-3800 controls the output transistor bias at a high speed in accordance with the level of the output signal. It prevents the output transistors from being set to the cut-off mode and helps eliminate higher harmonic distortion. As a result, the SX-3800 delivers a continuous power output of 60 watts per channel into an 8 ohms load from 20 to 20 kHz with no more than 0.005% total harmonic distortion.

According to the Pioneer database, this particular unit was manufactured in March 1981.

This unit came in with multiple issues.

1. The DC voltage measured across the speaker terminals is about 15mV on the right channel but was bouncing around 1V on the left channel. As a result, the protection relay clicks on and off cutting out the sound in both channels. Troubleshooting: the faulty HA12017 integrated circuit installed on the tone control board was replaced with a new one (refer to the "Tone Control Board") section for more detail.
2. There is pretty noticeable static in the left channel. Troubleshooting: the faulty HA12017 integrated circuit installed on the tone control board was replaced with a new one (refer to the "Tone Control Board") section for more detail.
3. No audio in FM mode if the FM Muting switch is in the ON position. Troubleshooting: this issue was resolved during the FM tuner alignment. The DC voltage between terminals 8 and 9 on the tuner assembly was around 2.64V. The N core of T2 was adjusted to 0V according to the service manual. 

Power Supply Board (GWR-122B)

The SX-3800 is certainly not a service-friendly receiver. A finned-style aluminum heat sink is mounted on the chassis between the power supply and power amplifier boards. As a result, the access to the foil side of both PCB's is limited and the heat sink should be disassembled from the chassis.

Finned-style aluminum heat sink

Heat sink removed

The power supply board (GWR-122B) has fifteen aluminum electrolytic capacitors C202, C203, C206 thru C210, C213 thru C217, C219, C223, and C227. All of them were replaced with low impedance and high-reliability Nichicon UPW/UPM caps. The max operating voltage was increased one step up on several e-caps.

The original electrolytic capacitors removed from this board have been tested with an Atlas ESR70 capacitance meter and the results are shown below. They are all still within +/- 20% of the factory capacitance tolerance and have fairly low ESR values. This is not a bad result, considering the age of this unit and the rather extreme operating conditions of the power supply board.

Test results on original capacitors removed from the power supply board:

C202: rated capacitance – 220uF, measured – 231uF, ESR – 0.01Ω, deviation: +5%

C203: rated capacitance – 220uF, measured – 228uF, ESR – 0.01Ω, deviation: +4%

C206: rated capacitance – 10uF, measured – 12uF, ESR – 1.12Ω, deviation: +20%

C207: rated capacitance – 47uF, measured – 47uF, ESR – 0.24Ω, deviation: 0%

C208: rated capacitance – 47uF, measured – 45uF, ESR – 0.28Ω, deviation: -4%

C209: rated capacitance – 47uF, measured – 47uF, ESR – 0.32Ω, deviation: 0%

C210: rated capacitance – 47uF, measured – 49uF, ESR – 0.27Ω, deviation: +4%

C213: rated capacitance – 470uF, measured – 447uF, ESR – 0.06Ω, deviation: -5%

C214: rated capacitance – 470uF, measured – 460uF, ESR – 0.04Ω, deviation: -2%

C215: rated capacitance – 1000uF, measured – 961uF, ESR – 0.01Ω, deviation: -4%

C216: rated capacitance – 100uF, measured – 112uF, ESR – 0.24Ω, deviation: +12%

C217: rated capacitance – 220uF, measured – 222uF, ESR – 0.12Ω, deviation: +1%

C219: rated capacitance – 470uF, measured – 520uF, ESR – 0.12Ω, deviation: +11%

C223: rated capacitance – 2.2uF, measured – 2.4uF, ESR – 1.27Ω, deviation: +9%

C227: rated capacitance – 10uF, measured – 11uF, ESR – 1.37Ω, deviation: +10%

All transistors on this (board except for Q202 and Q206) have also been replaced to improve the reliability of the power supply. They should be retired after working hard for the last 40+ years. Below is a list of original and replacement transistors I have used. Three transistors Q201, Q205, and Q209 are mounted on the heat sink. The old thermal pads were replaced with new Mica ones. The old thermal compound was refreshed with a new silicone thermal compound (Wakefield-Vette, 120 series).

Q201: NPN, 2SD313 (original), replaced with Fairchild MJE15032G

Q202: JFET, 2SK34 (original), retain, rarely fails

Q203: NPN, 2SC2320 (original), replaced with Fairchild KSC2383YTA

Q204: NPN, 2SC1915 (original), replaced with Fairchild KSC2690AYSTU

Q205: PNP, 2SB682 (original), replaced with Fairchild MJE15033G

Q206: JFET, 2SK34 (original), retain, rarely fails

Q207: PNP, 2SA912 (original), replaced with Fairchild KSA1013YBU

Q208: PNP, 2SA905 (original), replaced with Fairchild KSA1220AYS

Q209: NPN, 2SD313 (original), replaced with Fairchild MJE15032G

Q210: NPN, 2SD313 (original), replaced with Fairchild MJE15032G

Q211: NPN, 2SC2320 (original), replaced with Fairchild KSC2383YTA

Test results on the power supply board after servicing (FM program source, no signal):

pin 1: schematic: N/A, measured: 51.5VAC

pin 2: schematic: N/A, measured: 51.5VAC

pin 3: schematic: 0V, measured: 0V (ground)

pin 4: schematic: N/A, measured: 12.7VDC, 11.4VAC

pin 5: schematic: N/A, measured: 12.7VDC, 1.6VAC

pin 6: schematic: N/A, measured: +12.7V (Pilot lamps, PL1~3; Switch assembly, pin 1)

pin 7: schematic: N/A, measured: +12.7V (Pilot lamps, PL1~3; Switch assembly, pin 6)

pin 8: schematic: N/A, measured: 1.6VAC (FL tube, POWER, V2)

pin 9: schematic: N/A, measured: 1.6VAC (FL tube, POWER, V2)

pin 10: schematic: 0V, measured: 0V (ground)

pin 11: schematic: N/A, measured: -14V (FL tube, FREQUENCY, V1)

pin 12: schematic: N/A, measured: -14V (FL tube, FREQUENCY, V1)

pin 13: schematic: N/A, measured: +29.2V (Power Amp, pin 6)

pin 14: schematic: +19.5V, measured: +23.5V (Q11, pin 16)

pin 15: schematic: +12.8V, measured: +13.5V (Equalizer, pin 11)

pin 16: schematic: N/A, measured: +12.7V (Equalizer, pin 10)

pin 17: schematic: +5.5V, measured: +5.3V (Equalizer, pin 12)

pin 18: schematic: -47V, measured: -47.3V (Power Amp, pin 1)

pin 19: schematic: 0V, measured: 0V (ground)

pin 20: schematic: +47V, measured: +46.8V (Power Amp, pin 7)

pin 21: schematic: 0V, measured: 0V (ground)

pin 22: schematic: +32V, measured: +31.9V (Tone Control, pin 47; Equalizer, pin 1)

pin 23: schematic: -32V, measured: -32.6V (Tone Control, pin 46; Equalizer, pin 2)

pin 24: schematic: N/A, measured: -21.3V (Indicator Assembly, pin 4)

pin 25: schematic: -13V, measured: -14.2V (Tuner assembly, pin 2)

pin 26: schematic: N/A, measured: 34.4VAC

pin 27: schematic: N/A, measured: 34.4VAC

pin 28: schematic: 0V, measured: 0V (ground)

pin 29: schematic: +45.5V, measured: +45.6V (Power Amp, pin 31)

pin 30: schematic: 0V, measured: 0V (ground)

pin 31: schematic: -45.5V, measured: -45.6V (Power Amp, pin 32)

pin 32: schematic: 0V, measured: 0V (ground)

pin 33: schematic: 0V, measured: 0V (ground)

pin 34: schematic: 0V, measured: 0V (ground)

pin 35: schematic: +45.5V, measured: +45.6V (Power Amp, pin 14)

pin 36: schematic: 0V, measured: 0V (ground)

pin 37: schematic: -45.5V, measured: -45.6V (Power Amp, pin 13)

Power supply board - before and after servicing (sorry, I took a bad picture of this board due to a bunch of wires)

Filter Capacitors

I performed an in-circuit test on two large filter capacitors with Atlas ESR70 capacitance meter. Both caps are still within the factory capacitance tolerance and have very low ESR. So, I didn't change them. In general, the filter capacitors rarely fail in vintage gears, and I usually don't replace them unless their ESR is high.

In-circuit test on two filter capacitors - both are still in spec

C225: rated capacitance – 12000uF, measured – 11150uF, ESR – 0.02Ω, deviation: -7%

C226: rated capacitance – 12000uF, measured – 11620uF, ESR – 0.02Ω, deviation: -3%

Power Amplifier (GWH-139)

The power amplifier board has two low leakage e-caps (C101, C102) installed in the signal path, two bi-polar e-caps (C125, C126), and two aluminum electrolytic capacitors (C133, C134) installed in the protection circuit. The original low leakage e-caps were replaced with modern low leakage Nichicon UKL caps. Two bi-polar e-caps were replaced with replaced with film polyester Kemet caps. Finally, two aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the power amplifier board:

C101: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 2.5Ω, deviation: +9%

C102: rated capacitance – 4.7uF, measured – 5.0uF, ESR – 2.3Ω, deviation: +6%

C125: rated capacitance – 0.22uF, measured – 0.25uF, ESR – N/A, deviation: +14%

C126: rated capacitance – 0.22uF, measured – 0.25uF, ESR – N/A, deviation: +14%

C133: rated capacitance – 470uF, measured – 491uF, ESR – 0.11Ω, deviation: +5%

C134: rated capacitance – 100uF, measured – 97uF, ESR – 0.31Ω, deviation: -3%

Four transistors (Q109, Q110, Q115, and Q116) installed on the power amplifier board get very hot under normal operating conditions. The original transistors installed in these positions are 2SC1915 (Q109, Q110, NPN) and 2SA905 (Q115, Q116, PNP). The package type of original transistors is TO-92 with a thick collector lead, 0.84mm. The maximum collector power dissipation is 0.8W, which is insufficient for efficient heat dissipation. As a result, the long-term reliability of these transistors is always in doubt. I replaced the NPN transistors with a Fairchild KSC2690 and the PNP transistors with a Fairchild KSA1220. The maximum collector power dissipation of the new Fairchild transistors is 1.2W, which contributes to long-term reliability.

The original relay driver transistor on this board is 2SC1384. It usually degrades over time and I replaced it with a new Fairchild KSC2690. The new transistor has the same pinout as the original one. I tested the original transistor with Atlas DCA55 semiconductor analyzer and the measured current gain was only 63. According to the datasheet, the minimum gain for this transistor is supposed to be at least 120 (2SC1384, rank R). So, it always makes sense to replace the original relay driver transistor with a new one.

The original trimming resistors VR1/VR2 (470 kΩ, DC offset), VR3/VR4 (100 Ω, Bias), and VR5/VR6 (100 kΩ, Bias) were replaced with new Bourns potentiometers.

Power amplifier board - before and after servicing

Tone Control Board (GWG-141A)

The tone control board is probably the easiest board for servicing in comparison to all other PCBs in Pioneer SX-3800. However, to get the best access one should remove the front panel, disassemble the panel frame and remove three ribbon cables. Looks like a lot of work but the panel frame should be disassembled from the chassis in any case to get access to all controls. Otherwise, it is impossible to clean and lubricate all pots and switches behind this frame.

The front panel and panel frame removed

As I mentioned earlier, the DC voltage measured across the speaker terminals in this receiver was about 15mV on the right channel but fluctuated around 1V on the left channel. Initial diagnostics revealed a defective HA12017 integrated circuit installed in the left channel. The voltage measured on pins 1, 6, and 7 of Q1 (left channel) was different from the reference voltage on the schematic. In addition, the voltage on pin 6 was unstable and fluctuated around 3 V. The voltage measured on all pins of Q2 (right channel) was very close to the reference voltage on the schematic. I replaced the faulty HA12017 with a new one from old stock and normal operation was restored. The voltage across the speaker terminals on the left channel has stabilized at around 22mV. The static in the left channel has disappeared and the protection relay stopped clicking on and off.

Test results on HA12017 (Q1 & Q2) - the IC from the left channel is defective:

pin 1: schematic: 0V, measured: +25.9V (left); 61mV (right)

pin 3: schematic: N/A, measured: +20V (left); +19.5 (right)

pin 4: schematic: -25V, measured: -27.6V (left); -26.1 (right)

pin 5: schematic: N/A, measured: -28V (left); -24.9V (right)

pin 6: schematic: 0V, measured: -3V (left); 78mV (right)

pin 7: schematic: 0V, measured: +8.8V (left); 80mV (right)

pin 8: schematic: +25V, measured: +27.2V (left); +25.5 (right)

Test results on HA12017 (Q1 & Q2) after replacement the defective IC with a new one:

pin 1: schematic: 0V, measured: 40mV (left); 61mV (right)

pin 3: schematic: N/A, measured: +20.1V (left); +19.6 (right)

pin 4: schematic: -25V, measured: -25.9V (left); -26.2 (right)

pin 5: schematic: N/A, measured: -24.7V (left); -24.9V (right)

pin 6: schematic: 0V, measured: 53mV (left); 78mV (right)

pin 7: schematic: 0V, measured: 54mV (left); 80mV (right)

pin 8: schematic: +25V, measured: +25.3V (left); +25.6V (right)

The tone control board has fourteen low leakage e-caps (C1, C2, C15 thru C18, C21, C22, C25 thru C28, C33, C34) and eight aluminum e-caps (C7, C8, C13, C14, C 29 thru C32). All original low leakage e-caps with the rated capacitance of 1uF and lower were replaced with high-quality film polyester caps (WIMA and Kemet). The low leakage e-caps with higher rated capacitance were replaced with modern low leakage Nichicon UKL capacitors. The remaining aluminum e-caps were replaced with low impedance Nichicon UPW caps.  

Test results on original capacitors removed from the tone control board:

C1: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 1.8Ω, deviation: +9%

C2: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 2.0Ω, deviation: +9%

C7: rated capacitance – 100uF, measured – 100uF, ESR – 0.46Ω, deviation: 0%

C8: rated capacitance – 100uF, measured – 100uF, ESR – 0.48Ω, deviation: 0%

C13: rated capacitance – 47uF, measured – 43uF, ESR – 0.59Ω, deviation: -9%

C14: rated capacitance – 47uF, measured – 43uF, ESR – 0.66Ω, deviation: -9%

C15: rated capacitance – 0.22uF, measured – 0.22uF, ESR – N/A, deviation: 0%

C16: rated capacitance – 0.22uF, measured – 0.21uF, ESR – N/A, deviation: -5%

C17: rated capacitance – 1uF, measured – 1uF, ESR – 3.6Ω, deviation: 0%

C18: rated capacitance – 1uF, measured – 1uF, ESR – 4.0Ω, deviation: 0%

C21: rated capacitance – 0.33uF, measured – 0.35uF, ESR – N/A, deviation: 0%

C22: rated capacitance – 0.33uF, measured – 0.35uF, ESR – N/A, deviation: 0%

C25: rated capacitance – 1uF, measured – 1uF, ESR – 4.2Ω, deviation: 0%

C26: rated capacitance – 1uF, measured – 1.1uF, ESR – 4.2Ω, deviation: +10%

C27: rated capacitance – 10uF, measured – 11uF, ESR – 0.54Ω, deviation: +10%

C28: rated capacitance – 10uF, measured – 11uF, ESR – 0.52Ω, deviation: +10%

C29: rated capacitance – 47uF, measured – 48uF, ESR – 0.28Ω, deviation: +2%

C30: rated capacitance – 47uF, measured – 48uF, ESR – 0.22Ω, deviation: +2%

C31: rated capacitance – 47uF, measured – 48uF, ESR – 0.23Ω, deviation: +2%

C32: rated capacitance – 47uF, measured – 50uF, ESR – 0.22Ω, deviation: +6%

C33: rated capacitance – 10uF, measured – 11uF, ESR – 0.46Ω, deviation: +10%

C34: rated capacitance – 10uF, measured – 11uF, ESR – 0.52Ω, deviation: +10%

Tone control board - before and after servicing

Equalizer Amplifier Board (AWM-227A)

To service this board, one should remove four plastic arms for the function controls, four ribbon cables, and then disassemble it from the rear panel.

The equalizer amplifier board has four low leakage capacitors (C3, C4, C23, C24) installed in the signal path, and six aluminum e-caps (C1, C2, C9, C10, C21, C22). The low leakage capacitors were replaced with modern low leakage Nichicon UKL capacitors. And the remaining aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the equalizer amplifier board:

C1: rated capacitance – 47uF, measured – 49uF, ESR – 0.34Ω, deviation: +4%

C2: rated capacitance – 47uF, measured – 50uF, ESR – 0.27Ω, deviation: +6%

C3: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 1.81Ω, deviation: +9%

C4: rated capacitance – 4.7uF, measured – 5.0uF, ESR – 2.21Ω, deviation: +6%

C9: rated capacitance – 470uF, measured – 557uF, ESR – 0.09Ω, deviation: +19%

C10: rated capacitance – 470uF, measured – 511uF, ESR – 0.08Ω, deviation: +9%

C21: rated capacitance – 47uF, measured – 49uF, ESR – 0.27Ω, deviation: +4%

C22: rated capacitance – 47uF, measured – 48uF, ESR – 0.26Ω, deviation: +2%

C23: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 1.89Ω, deviation: +9%

C24: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 2.81Ω, deviation: +9%

Equalizer amplifier board - before and after servicing

FL Indicator Board (AWV-009)

To release this board for servicing one should disassemble a lot of stuff: the front panel, the panel frame, and the dial panel. In that case, it is possible to service this board without a dial cord re-stringing. It is still not an easy task but doable with a lot of patience and luck.

Tough access to the FL indicator board

The FL indicator board has two low leakage capacitors (C1, C2) and 12 aluminum e-caps (C3, C10, C16, C28, C31, C33 thru C39). The original low leakage e-caps as well as aluminum e-caps C3, C33 thru C39 were replaced with film polyester WIMA caps. The remaining aluminum capacitors were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the equalizer amplifier board:

C1: rated capacitance – 1uF, measured – 1uF, ESR – 4.7Ω, deviation: 0%

C2: rated capacitance – 1uF, measured – 1uF, ESR – 4.1Ω, deviation: 0%

C3: rated capacitance – 0.47uF, measured – 0.52uF, ESR – N/A, deviation: %

C10: rated capacitance – 100uF, measured – 115uF, ESR – 0.21Ω, deviation: +15%

C16: rated capacitance – 470uF, measured – 496uF, ESR – 0.06Ω, deviation: +6%

C28: rated capacitance – 470uF, measured – 508uF, ESR – 0.07Ω, deviation: +8%

C31: rated capacitance – 220uF, measured – 203uF, ESR – 0.22Ω, deviation: -8%

C33: rated capacitance – 1uF, measured – 1uF, ESR – 1.59Ω, deviation: 0%

C34: rated capacitance – 1uF, measured – 1uF, ESR – 1.73Ω, deviation: 0%

C35: rated capacitance – 1uF, measured – 1uF, ESR – 1.72Ω, deviation: 0%

C36: rated capacitance – 1uF, measured – 1uF, ESR – 1.68Ω, deviation: 0%

C37: rated capacitance – 1uF, measured – 1uF, ESR – 1.76Ω, deviation: 0%

C38: rated capacitance – 1uF, measured – 0.9uF, ESR – 1.67Ω, deviation: -10%

C39: rated capacitance – 1uF, measured – 0.9uF, ESR – 1.65Ω, deviation: -10%

FL indicator board - before and after servicing

Dial Lamps

All original dial lamps in this unit were replaced with new incandescent lamps (8V, wedge base). Each lamp is very easy to replace without damaging the brittle lamp socket if you use the following tip below.

Tip: there is a small opening at the center of each lamp socket. I used a small Allen wrench and gently pushed each lamp out of the socket. In that case, the brittle socket tabs won't be damaged or broken.

DC offset and Bias Adjustments

At the end of my restoration, I adjusted the DC offset and Bias on the power amplifier according to the service manual.

The DC offset on the left channel is measured between pin 23 and ground. On the right channel, it is measured between pin 22 and ground. It is pretty hard to reach these two pins due to limited access. But the multimeter can be directly connected to the speaker terminals to adjust the DC offset. Just make sure to depress the switch (A or B) corresponding to the SPEAKERs terminals on the rear panel. The DC offset should be adjusted as close to zero volts as possible with the trimming resistors VR1 and VR2.

The Bias on the left channel is measured between pins 28 (+) and 25 (-). On the right channel, it is measured between pins 17 (+) and 20 (-). It should be adjusted to ~120mV with the trimming resistors VR3 and VR4. And then, to ~150mV with the trimming resistors VR5 and VR6. I adjusted the bias on each channel to about 10mV lower than the manual recommends. Based on my experience, the bias is usually drifting to higher values over time in this model (as well as in model SX-3900).

DC offset on the left and right channels after restoration

Bias on the left and right channels after restoration

Output Power Test

The final output power test was performed at the end of my restoration. The amplifier was loaded with a low inductance 8Ω/100W dummy resistor for each channel. The oscilloscope was connected across the speaker terminals and a sine-wave signal of 1kHz was applied to the AUX jacks. The output sine-wave signal was perfectly symmetrical on both channels with no clipping up to 22.65 VRMS (left channel) and 23.34 VRMS (right channel). It corresponds to the output power of 64.1W on the left channel and 68.1W on the right channel.

Output power test

As usual, all the knobs and the front panel were gently cleaned in warm water with dish soap. All controls have been cleaned with DeoxIT 5% contact cleaner and lubricated with DeoxIT FaderLube 5% spray.

The final result can be seen in the photos below. The receiver looks and sounds great again. Please watch a short demo video at the end of this post. Thank you for reading.

Pioneer SX-3800 - after restoration

Demo video after repair & restoration