Sansui 9090 Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Sansui

Model: 9090

SN: 825110866

In the golden age of Hi-Fi audio, the Sansui 9090 was one of the most advanced and attractive receivers that any audiophile would want to own. This model was introduced in 1975 and at the time was Sansui's top receiver in the production line: 9090, 8080, 7070, 6060, and 5050. It features two large power meters, signal strength and tuning meters, a power protection circuit with an LED indicator, triple tone control with turnover selectors, two tape deck terminals, a Dolby FM/4-channel adaptor, a wide dynamic range from precise phono equalization system, a full range of controls, connections for three sets of speaker systems and FM Multipath detection system. The Sansui 9090 has a quasi-complementary power stage with eight original Sanken 2SC1116 NPN transistors. It delivers 110 watts per channel into 8 ohms with no more than 0.2% total harmonic distortion. The top cover is made from natural wood. The low-end models have simulated wood pattern vinyl. The Sansui 9090 is simply a holy grail and one of the best receivers ever made!

As I mentioned earlier, the Sansui 9090 was introduced to the market in 1975. In April 1976, Sansui issued a service bulletin to address a major problem that might occur when both A and B speakers are running simultaneously. To solve this issue, Sansui recommended modifying the following circuit boards: F-2546 (Power Supply Board), F-2436 (Driver Circuit Board), and F-2547 (Protection Circuit Board). This modification has been made at the factory for all units (models 9090 and 8080) since April 1976. The receiver I have on my bench today was manufactured in November 1975 and the recommended modification was not carried out. I will describe each board's modification in the following sections below.

Power Supply Board (F-2546)

The following modifications on the power supply board (F-2546) have to be done for all units manufactured before April 1976:

1. Four fuses F07, F08, F09, and F10 are originally rated at 6A and must be replaced with 10A fuses.

2. The jumpers in positions F03 and F04 must be removed and new fuse holders must be installed. Two new 10A fuses must be installed in these positions.

3. A thick, well-conducting wire must be connected between point 03 and the ground lug to improve the ground contact on the PCB F-2546.

4. The jumpers between points 38 and 36, and between points 37 and 35 must be removed.

5. The wire must be connected between point 04 on F-2547 (Protection circuit) to point 35 on F-2546.

6. The wire must be connected between point 03 on F-2547 (Protection circuit) to point 36 on F-2546.

The first item from the list above was very easily solved with new 10A fuses. 

The second item was a little tricky. The distance between the fuse clips in positions F03 and F04 is too small to accommodate a conventional 3AG-type fuse (6.3mm x 32mm). So I installed new 2AG fuse clips in these positions and a new 10A 2AG-type (5mm x 20mm) fuse.

To improve the ground contact, I used a piece of 16 AWG wire with a ring terminal.

Improved ground contact on the PCB F-2546

The jumpers between points 38 and 36, and between points 37 and 35 were easily removed with a little help from my Hakko FR301 desoldering tool. 

Jumpers between points 38 and 36, and between points 37 and 35 (all units manufactured before April 1976)

Jumpers are removed. Don't be confused with the yellow wires. These wires are still soldered to points 38 and 37, respectively. But they were resoldered to the additional foil pads on the PCB (see the picture below for the foil side of the power supply board after servicing) 

Now it's time for routine servicing. The power supply board has 5 aluminum electrolytic capacitors (C01, C02, C03, C04, C05) soldered on the front side of the PCB and 2 aluminum e-caps (2.2uF/100V) soldered on the back (foil) side of the PCB. 

All capacitors soldered on the front side of this board were replaced with low impedance Nichicon UPW/UPM caps. Two additional e-caps soldered on the back side were replaced with wide temperature range Nichicon UVY caps.

The original e-caps were tested with an Atlas ESR70 capacitance meter; the results are below.

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

C01: rated capacitance – 1000uF, measured – 715uF, ESR – 0.08Ω, deviation: -29%

C02: rated capacitance – 220uF, measured – 278uF, ESR – 0.11Ω, deviation: +26%

C03: rated capacitance – 100uF, measured – 112uF, ESR – 0.27Ω, deviation: +12%

C04: rated capacitance – 47uF, measured – 53uF, ESR – 0.36Ω, deviation: +13%

C05: rated capacitance – 100uF, measured – 113uF, ESR – 0.25Ω, deviation: +13%

C (foil side): rated capacitance – 2.2uF, measured – uF, ESR – Ω, deviation: %

C (foil side): rated capacitance – 2.2uF, measured – uF, ESR – Ω, deviation: %

I also replaced all transistors on this board to improve the reliability of the power supply. Below is a list of original and replacement transistors that I have used. A fresh silicone thermal compound (Wakefield-Vette, 120 series) was applied between the new MJE15032G transistor installed in position TR02 and the heat sink.

TR01: NPN, 2SC1211 (original), replaced with a new KSC2383YTA

TR02: NPN, 2SD313 (original), replaced with a new MJE15032G

TR03: NPN, 2SC1211 (original), replaced with a new KSC2383YTA

The potential leakage of the original Zener diode (ZD01) on this board might cause the breakdown of the protection relay as noted in the service bulletin. I replaced it with a new Onsemi 1N5243B (13V/0.5W) Zener diode as a part of preventive maintenance.

Power supply board - before servicing (the driver board is removed)

Power supply board - after servicing

Driver Circuit Board (F-2436)

The following modifications on the driver circuit board (F-2436) have to be done for all units manufactured before April 1976:

1. Check if the two points of coils L01 and L02 are connected by a jumper. If so, then remove the jumper.

2. Two wire-in 7A fuses must be soldered between pins 3 and 4, and between pins 15 and 16, respectively.

This particular PCB (F-2436-1) has no coils. These coils were probably installed in the early days of production.

I soldered two 7A fuses between the corresponding contacts. The body and leads of each fuse were insulated with pieces of heat shrink tubing. Pay attention to this step. New fuses must be securely isolated from other PCB components.

The driver circuit board has 2 low leakage e-caps (C01, C02) installed in the signal path, 2 bi-polar e-caps (C07, C08), and 2 aluminum electrolytic capacitors (C11, C12).

The original low leakage capacitors were replaced with high-quality film polyester WIMA caps. Two bi-polar e-caps were replaced with modern bi-polar Nichicon UEP caps. And two original filtering e-caps (C11, C12) were replaced with low impedance Nichicon UPM capacitors.

Test results on original capacitors removed from the driver circuit board:

C01: rated capacitance – 0.47uF, measured – 0.44uF, ESR – N/A, deviation: -6%

C02: rated capacitance – 0.47uF, measured – 0.43uF, ESR – N/A, deviation: -9%

C07: rated capacitance – 100uF, measured – 118uF, ESR – 0.51Ω, deviation: +18%

C08: rated capacitance – 100uF, measured – 120uF, ESR – 0.36Ω, deviation: +20%

C11: rated capacitance – 100uF, measured – 121uF, ESR – 0.14Ω, deviation: +21%

C12: rated capacitance – 100uF, measured – 123uF, ESR – 0.22Ω, deviation: +23%

The original fusible resistors (R29, R30, R39, R40, R43, R44, R47, R48, R49, R50) on this board were replaced with metal film KOA Speer resistors. One original fusible resistor (R40) was found open. Another one (R43) drifted from the nominal value by more than 14%.

The original trimming resistors were also replaced with new Bourns potentiometers.

Driver circuit board - before and after

Equalizer Circuit Board (F-2541)

The equalizer circuit board has 4 low leakage e-caps (C03, C04, C11, C12) installed in the signal path, and 5 aluminum electrolytic capacitors (C05, C06, C09, C10, C601).

Two original low leakage e-caps (C03, C04) installed in the input signal path were replaced with modern low leakage Nichicon UKL caps. The low leakage e-caps (C11, C12) installed in the output signal path were replaced with film polyester WIMA caps. The remaining aluminum e-caps except C601 were replaced with low impedance Nichicon UPW/UHE caps. The e-cap C601 was replaced with a film polyester WIMA cap.

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

C03: rated capacitance – 3.3uF, measured – 2.9uF, ESR – 2.4Ω, deviation: -12%

C04: rated capacitance – 3.3uF, measured – 2.9uF, ESR – 2.8Ω, deviation: -12%

C05: rated capacitance – 470uF, measured – 553uF, ESR – 0.04Ω, deviation: +18%

C06: rated capacitance – 470uF, measured – 552uF, ESR – 0.09Ω, deviation: +17%

C09: rated capacitance – 47uF, measured – 56uF, ESR – 0.71Ω, deviation: +19%

C10: rated capacitance – 47uF, measured – 54uF, ESR – 0.68Ω, deviation: +15%

C11: rated capacitance – 1uF, measured – 1uF, ESR – 3.3Ω, deviation: 0%

C12: rated capacitance – 1uF, measured – 1uF, ESR – 3.6Ω, deviation: 0%

C601: rated capacitance – 1uF, measured – 1.2uF, ESR – 3.4Ω, deviation: +20%

Equalizer circuit board - before and after

Accessory Switch Board (F-2542)

This board has only one aluminum electrolytic capacitor C601. I replaced it with a low impedance Nichicon UPW cap.

Test results on original capacitors removed from the accessory switch board:

C601: rated capacitance – 33uF, measured – 40uF, ESR – 0.31Ω, deviation: +21%

Accessory switch board - before and after

Tone Control Board (F-2543)

The tone control board (F-2543) has 4 low leakage e-caps (C603, C604, C607, C611) and 3 aluminum electrolytic capacitors (C606, C609, C610). 

Two original low leakage e-caps (C603, C604) with a rated capacitance of 2.2uF were replaced with film polyester WIMA caps. The other 2 low leakage e-caps were replaced with modern low leakage Nichicon UKL caps. The remaining aluminum e-caps were replaced with low impedance Nichicon UPW/UPM caps.

Test results on original capacitors removed from the tone control board (F-2543):

C603: rated capacitance – 2.2uF, measured – 1.9uF, ESR – 3.2Ω, deviation: -14%

C604: rated capacitance – 2.2uF, measured – 1.9uF, ESR – 3.9Ω, deviation: -14%

C606: rated capacitance – 47uF, measured – 51uF, ESR – 1.77Ω, deviation: +9%

C607: rated capacitance – 1uF, measured – 1uF, ESR – 4.1Ω, deviation: 0%

C609: rated capacitance – 100uF, measured – 114uF, ESR – 0.11Ω, deviation: +14%

C610: rated capacitance – 470uF, measured – 536uF, ESR – 0.12Ω, deviation: +14%

C611: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 2.1Ω, deviation: +9%

The original 2SC1313 transistor installed in position TR601 is on my list of transistors that are prone to failure. I replaced it with a new low-noise Fairchild KSC1845 transistor. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

Tone control board (F-2543)  - before and after

Tone Control Board (F-2544)

The tone control board (F-2544) has 8 low leakage e-caps (C01, C02, C05, C06, C27, C28, C31, C32) installed in the signal path, and 6 aluminum electrolytic capacitors (C09, C10, C33, C34, C601, C602).

The original low leakage capacitors with a rated capacitance of 1uF and 2.2uF were replaced with film polyester WIMA caps. The other 4 low leakage e-caps were replaced with modern low leakage Nichicon UKL caps. And the remaining aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the tone control board (F-2544):

C01: rated capacitance – 1uF, measured – 0.9uF, ESR – 4.6Ω, deviation: -10%

C02: rated capacitance – 1uF, measured – 0.9uF, ESR – 3.7Ω, deviation: -10%

C05: rated capacitance – 10uF, measured – 11uF, ESR – 1.87Ω, deviation: +10%

C06: rated capacitance – 10uF, measured – 11uF, ESR – 3.1Ω, deviation: +10%

C09: rated capacitance – 47uF, measured – 54uF, ESR – 0.84Ω, deviation: +15%

C10: rated capacitance – 47uF, measured – 52uF, ESR – 0.91Ω, deviation: +11%

C27: rated capacitance – 2.2uF, measured – 1.9uF, ESR – 3.9Ω, deviation: -14%

C28: rated capacitance – 2.2uF, measured – 1.9uF, ESR – 2.6Ω, deviation: -14%

C31: rated capacitance – 10uF, measured – 11uF, ESR – 1.44Ω, deviation: +10%

C32: rated capacitance – 10uF, measured – 11uF, ESR – 1.12Ω, deviation: +10%

C33: rated capacitance – 220uF, measured – 225uF, ESR – 0.37Ω, deviation: +2%

C34: rated capacitance – 220uF, measured – 226uF, ESR – 0.44Ω, deviation: +3%

C601: rated capacitance – 470uF, measured – 574uF, ESR – 0.31Ω, deviation: +22%

C602: rated capacitance – 220uF, measured – 252uF, ESR – 0.22Ω, deviation: +15%

The prone-to-failure 2SC1313 transistor installed in positions TR01 & TR02 was replaced with a new low-noise Fairchild KSC1845 transistor. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

Tone control board (F-2544) - before and after

Filter & Muting Circuit Board (F-2545)

The filter & muting circuit board has only 2 low leakage e-caps (C05, C06) installed in the signal path. I replaced them with film polyester WIMA caps.

Test results on original capacitors removed from the filter & muting circuit board:

C05: rated capacitance – 2.2uF, measured – 1.8uF, ESR – 2.3Ω, deviation: -18%

C06: rated capacitance – 2.2uF, measured – 1.9uF, ESR – 2.2Ω, deviation: -14%

Filter & muting circuit board - before and after

Protection Circuit Board (F-2547)

The following modifications on the protection circuit board (F-2547) have to be done for all units manufactured before April 1976:

1. Two resistors (R13 & R14) rated at 10Ω, 1W have to be replaced with resistors of 4.7Ω, 1/2W.

2. The jumper connecting some relay contacts to the ground has to be removed.

To address the first issue, I replaced the original resistors R13 and R14 with metal film KOA Speer resistors (4.75Ω, 1/2W). The jumper connecting some relay contacts to the ground was also removed (refer to the picture below, the jumper is soldered between the relay's contact and resistor R06).

The protection circuit board has 2 bi-polar capacitors (C05, C12) and 6 aluminum electrolytic capacitors (C01, C02, C03, C04, C06, C07).

The original bi-polar capacitor C05 was replaced with a modern bi-polar Nichicon UEP cap. Another bi-polar capacitor C12 and the e-caps C04, C06, and C07 with a nominal capacitance of 1uF were replaced with film polyester WIMA caps. The remaining aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the protection circuit board:

C01: rated capacitance – 33uF, measured – 38uF, ESR – 0.34Ω, deviation: +15%

C02: rated capacitance – 220uF, measured – 235uF, ESR – 0.14Ω, deviation: +7%

C03: rated capacitance – 470uF, measured – 498uF, ESR – 0.09Ω, deviation: +6%

C04: rated capacitance – 1uF, measured – 1.1uF, ESR – 2.1Ω, deviation: +10%

C05: rated capacitance – 47uF, measured – 50uF, ESR – 1.1Ω, deviation: +6%

C06: rated capacitance – 1uF, measured – 1.1uF, ESR – 2.4Ω, deviation: +10%

C07: rated capacitance – 1uF, measured – 1.2uF, ESR – 2.3Ω, deviation: +20%

C12: rated capacitance – 1uF, measured – 1uF, ESR – 3.6Ω, deviation: 0%

The original trimming resistors (VR01 and VR02) used to adjust the power meters were replaced with new Bourns potentiometers.

Finally, the original protection relay was replaced with a new Omron relay to improve overall reliability.

Protection circuit board - before and after

Power Supply Board (F-2431)

The power supply board (F-2431) has 3 aluminum electrolytic capacitors: C01, C02, and C901. All of them were replaced with low impedance Nichicon UPW/UPM caps.

Test results on original capacitors removed from the power supply (F-2431) board:

C01: rated capacitance – 220uF, measured – 221uF, ESR – 0.31Ω, deviation: 0%

C02: rated capacitance – 100uF, measured – 111uF, ESR – 0.43Ω, deviation: +11%

C901: rated capacitance – 470uF, measured – 507uF, ESR – 0.19Ω, deviation: +8%

Power supply board (F-2431) - before and after

Multi-Path Circuit Board (F-2550)

The multi-path circuit board has 3 aluminum electrolytic capacitors: C01, C03, and C04.

The original e-cap C01 with a nominal capacitance of 1uF was replaced with a film polyester WIMA cap. The remaining e-caps were replaced with low impedance Nichicon UPW caps. Pay attention to the polarity of the e-cap C04 (10uF/16V). The polarity on the silkscreen is backward!

Test results on original capacitors removed from the multi-path circuit board:

C01: rated capacitance – 1uF, measured – 1.2uF, ESR – 2.1Ω, deviation: +20%

C03: rated capacitance – 4.7uF, measured – 5.5uF, ESR – 2.6Ω, deviation: +17%

C04: rated capacitance – 10uF, measured – 11uF, ESR – 3.8Ω, deviation: +10%

The original 2SC711 NPN transistor installed in positions TR01 and TR02 is on my list of transistors that are prone to failure. I replaced it with a new low-noise Fairchild KSC1845 transistor. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

Multi-path circuit board - before and after

Power Transistors

The original Sanken 2SC1116A power transistors were removed from the chassis, degreased with isopropanol, and tested with an Atlas DCA55 semiconductor analyzer. Each pair of transistors is still matched very well by the current gain and base-emitter voltage. I mounted all the power transistors back and applied fresh thermal paste. The old thermal pads were also replaced with new Mica ones.

Test results on original Sanken 2SC1116A power transistors:

TR701: hfe - 48, Vbe - 0.585V

TR702: hfe - 48, Vbe - 0.583V

TR703: hfe - 58, Vbe - 0.592V

TR704: hfe - 53, Vbe - 0.591V

TR705: hfe - 45, Vbe - 0.596V

TR706: hfe - 46, Vbe - 0.597V

TR707: hfe - 55, Vbe - 0.591V

TR708: hfe - 51, Vbe - 0.594V

Power transistors - before servicing, very dusty heat sink

Power transistors - before servicing, the heat sink removed

Power transistors - new Mica pads and fresh thermal paste

Dial Lamps

To replace the dial lamps one should remove two small screws from the top of the chassis that hold the plastic lamp reflector. I replaced the original incandescent lamps with warm white LED lamps to maintain the original look and decrease heat.

New warm white LED lamps

Signal Strength and Tuning Meter Lamps

I do prefer to use warm white LED lamps in vintage receivers because their color temperature is close to that of incandescent lamps. In addition, the LED lamps produce a lower amount of heat in comparison to the incandescent lamps thereby protecting the plastic parts of lamp holders/reflectors from overheating. However, I found the warm white LED lamps to be too bright if they are installed behind the meters. So, I decided to stick with the original design and installed new incandescent lamps here. The meter lamps can be easily replaced with LED lamps in the future if necessary.

Power Meter Lamps

The power meter lamps are very difficult to replace in the Sansui 9090 due to the limited space to work with. In addition, original rubber bushings often wear out over time due to overheating. Initially, I tried to replace the old rubber bushings with modern ones available on the market. However, modern bushings do not hold lamps well due to their primitive design compared to the original bushings. Fortunately, the original rubber bushings in this unit are still in very good condition and I was able to use them again without loss of quality. In any case, replacing power meter lamps in Sansui 9090 is very tedious work.

Power meter lamps - before and after

Filter Capacitors

Two main filter capacitors were tested with Atlas ESR70 capacitance meter (in-circuit test). Both caps are still within the factory capacitance tolerance and have almost zero 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

C703: rated capacitance – 6800uF, measured – 6887uF, ESR – 0.04Ω, deviation: +1%

C704: rated capacitance – 6800uF, measured – 6683uF, ESR – 0.02Ω, deviation: -2%

DC offset and Idling Current Adjustments

The DC offset is measured across speaker terminals on each channel. It should be adjusted as close to zero volts as possible with the trimming resistors VR01 and VR02, respectively.

To adjust the idling current one should remove the fuse from the left (right) channel and connect the DC ammeter between the terminals of the fuse holder. Then the idling current should be adjusted to 50mA +/- 1mA with the trimming resistor VR03 (VR04).

DC offset on the left and right channels after restoration

Idling current 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 receiver 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 29.38 VRMS (left channel) and 29.04 VRMS (right channel). It corresponds to the output power of 107.9W on the left channel and 105.4W on the right channel. I was not able to test this receiver above its 110W rating simply because my current dummy resistor can only dissipate 100W max (I probably need to invest some money and buy additional dummy resistors that can dissipate around 200W).

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. This receiver from the 70s is a real gem - beautiful looks, solid design, and amazing sound. Please watch a short demo video at the end of this post. Thank you for reading.

Sansui 9090 - after restoration

Demo video after repair & restoration

Marantz 2275 Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Marantz

Model: 2275

SN: P080125

Today I'm showcasing a Marantz 2275 vintage receiver that came in for restoration.  This model is the successor to the famous Marantz 2270 manufactured from 1972 to 1974. The Marantz 2275 is another step forward and is considered one of the best Marantz receivers ever. This model was manufactured from 1975 to 1977. It delivers 75 watts per channel into 8 ohms with no more than 0.25% total harmonic distortion. The optional walnut veneer cabinet for this model is WC-22.

This particular unit is a European version equipped with a universal power transformer. According to the factory stamp on the chassis, this receiver was manufactured in October 1976.

Power Supply & Protection Relay Circuit (P800)

The power supply & protection relay circuit board has 8 aluminum electrolytic capacitors: C801, C802, C804, C805, C806, C807, C808, and C809. 

I replaced all capacitors on this board with low impedance Nichicon UPW/UPM caps.

The original e-caps were tested with an Atlas ESR70 capacitance meter; the results are below.

Test results on original capacitors removed from the power supply & protection relay circuit board:

C801: rated capacitance – 220uF, measured – 244uF, ESR – 0.15Ω, deviation: +11%

C802: rated capacitance – 100uF, measured – 126uF, ESR – 0.12Ω, deviation: +26%

C804: rated capacitance – 22uF, measured – 25uF, ESR – 0.28Ω, deviation: +14%

C805: rated capacitance – 330uF, measured – 346uF, ESR – 0.11Ω, deviation: +5%

C806: rated capacitance – 470uF, measured – 467uF, ESR – 0.31Ω, deviation: -1%

C807: rated capacitance – 10uF, measured – 12uF, ESR – 0.43Ω, deviation: +20%

C808: rated capacitance – 47uF, measured – 54uF, ESR – 0.62Ω, deviation: +15%

C809: rated capacitance – 220uF, measured – 280uF, ESR – 0.16Ω, deviation: +27%

I also replaced all transistors on this board to improve the reliability of the power supply. Below is a list of original and replacement transistors that I have used. A fresh silicone thermal compound (Wakefield-Vette, 120 series) was applied between the new MJE15030G transistor installed in position H804 and the heat sink.

Q801: NPN, 2SD330 (original), replaced with a new Fairchild MJE15030G

Q802: NPN, 2SC1318 (original), replaced with a new Fairchild KSC2690AYSTU

Q803: NPN, 2SC945 (original), replaced with a new Fairchild KSC2383YTA

Q804: NPN, 2SD331 (original), replaced with a new Fairchild MJE15030G

Q805: NPN, 2SC945 (original), replaced with a new Fairchild KSC945CYTA

Q806: NPN, 2SC1318 (original), replaced with a new Fairchild KSC2383YTA

Q807: NPN, 2SC1318 (original), replaced with a new Fairchild KSC2383YTA

The original trimming resistor R806 on this board was also replaced with a new Bourns potentiometer.

Finally, the original protection relay was replaced with a new Omron relay to improve overall reliability.

After the servicing, the voltage between pin J804 and J805 (ground) was adjusted to +35.0V DC with trimming resistor R806.

Power supply & protection relay circuit board - voltage regulator adjustment

Power supply & protection relay circuit board - before and after

Power Amplifier Board (P700)

There are two power amplifier boards in Marantz 2275. Each board is mounted directly on the heatsink with two power transistors. The entire assembly can be easily removed from the chassis for servicing. This thoughtful engineering design makes life easier for technicians.

Power amplifier board - removed from the chassis

Each board has one low leakage e-cap C702 and 2 ordinary aluminum electrolytic capacitors (C703 and C704). 

The original low leakage e-cap was replaced with modern low leakage Nichicon UKL cap. And, the remaining aluminum e-caps were replaced with low impedance Nichicon UPW caps.

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

Left channel

C702: rated capacitance – 47uF, measured – 45uF, ESR – 0.36Ω, deviation: -4%

C703: rated capacitance – 10uF, measured – 13uF, ESR – 2.6Ω, deviation: +30%

C704: rated capacitance – 10uF, measured – 12uF, ESR – 1.51Ω, deviation: +20%

Right channel

C702: rated capacitance – 47uF, measured – 47uF, ESR – 0.51Ω, deviation: 0%

C703: rated capacitance – 10uF, measured – 13uF, ESR – 161Ω, deviation: +30%

C704: rated capacitance – 10uF, measured – 13uF, ESR – 3.1Ω, deviation: +30%

The first stage of the power amplifier circuit is a differential amplifier consisting of two amplifying transistors with a common emitter: H701 and H702. The original NPN transistors installed in these positions are 2SC1327. These transistors are not on my list of infamous transistors that are prone to failure. But, I decided to unsolder the original transistors and test them to make sure that they are still well matched by current gain.

Testing showed that both pairs of 2SC1327s are matched within ~3% in terms of current gain. This is a very good result for almost 50 years old electronic components. However, I decided to replace each pair of original 2SC1327 transistors with new close matched pair of modern low-noise Fairchild KSC1845s. Two transistors installed in a differential amplifier are supposed to be precisely matched to work properly in the circuit. So, it always makes sense to replace the old electronic components installed in the critical positions with new high quality parts. Each pair of new KSC1845 transistors was carefully matched (within ~1%) by current gain and base-emitter voltage.

I put a slight smear of new thermal paste on one face of KSC1845 and pressed both transistors together. A piece of heat shrink tubing was used to hold them together mechanically as in the original transistors.

Test results on original 2SC1327 transistors

H701 (left channel): hfe - 557, Vbe - 0.757V 

H702 (left channel): hfe - 572, Vbe - 0.757V

H701 (right channel): hfe - 676, Vbe - 0.758V 

H702 (right channel): hfe - 692, Vbe - 0.759V

Test results on new KSC1845 transistors

H701 (left channel): hfe - 443, Vbe - 0.749V 

H702 (left channel): hfe - 440, Vbe - 0.749V

H701 (right channel): hfe - 439, Vbe - 0.750V 

H702 (right channel): hfe - 437, Vbe - 0.749V

The original 2SA721 pre-driver transistor installed in position H703 is on my list of transistors that are prone to failure. I replaced it with a new low-noise Fairchild KSA992 transistor. The original 2SC1327 transistor installed in position H704 was also replaced with modern low-noise Fairchild KSC1845 since it is complemented to 2SA721.

Power amplifier board - before and after (only one board is shown)

Phono Amplifier Board (P400)

The phono amplifier board has 2 solid tantalum capacitors (C401, C402) installed in the input signal path, 2 low leakage e-caps (C403, C404), and an aluminum filtering e-cap C413. 

The original tantalum capacitors were replaced with high-quality film polyester WIMA caps. The original low leakage e-caps were replaced with modern low leakage Nichicon UKL caps. The design of the printed circuit board allows the installation of an axial or radial capacitor in position C413. I replaced the original axial e-cap C413 with a radial type low impedance Nichicon UPW cap.

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

C401: rated capacitance – 1uF, measured – 1uF, ESR – 11.8Ω, deviation: 0%

C402: rated capacitance – 1uF, measured – 1uF, ESR – 3.2Ω, deviation: 0%

C403: rated capacitance – 47uF, measured – 61uF, ESR – 0.48Ω, deviation: +30%

C404: rated capacitance – 47uF, measured – 60uF, ESR – 0.46Ω, deviation: +28%

C413: rated capacitance – 100uF, measured – 119uF, ESR – 1.46Ω, deviation: +19%

The original 2SC1344 Hitachi NPN transistor installed in positions H401 to H404 is on my list of transistors that are prone to failure. I replaced all 2SC1344s with low-noise Fairchild KSC1845 transistors. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB. Also, make sure that the new transistors installed in the first stage of the phono stage have a high current gain of 400 or more.

The original 2SC1775 Hitachi NPN transistor installed in positions H405 and H406 was also replaced with low-noise Fairchild KSC1845 transistor. The replacement transistor has the same pinout as the original one.

The failure-prone VD1212 dual diode installed in position H409 was replaced with a pair of 1N4148 diodes in series.

Phono amplifier board - before and after

Power Transistors

All original power transistors were removed, degreased, and tested with Atlas DCA55 semiconductor analyzer. The test showed that the NPN transistor H004 has a shunt between the base and the emitter. The measured resistance between the base and emitter was very low at ~16.1kΩ. The remaining three transistors passed the test. 

I did not find a datasheet for the original power transistors installed in this unit. However, both transistors (S40443 and S40442) from the left channel have a relatively low current gain of ~28. Because of all these problems, I decided to replace the original power transistors in each channel with new ON Semiconductor MJ21194G / MJ21193G transistors. The new transistors are specifically designed for high-power audio output, have excellent gain linearity, and complement each other. The new Mica pads and fresh thermal compound were applied between each power transistor and heat sink.

Test results on original power transistors:

H001, S40442, PNP, hfe = 29, Vbe = 0.564V

H002, S40443, NPN, hfe = 28, Vbe = 0.597V

H003, S40442, PNP, hfe = 76, Vbe = 0.581V

H004, S40443, NPN, shunt between the base and the emitter

Test results on new ON Semiconductor power transistors:

H001, MJ21193G, PNP, hfe = 74, Vbe = 0.592V

H002, MJ21194G, NPN, hfe = 54, Vbe = 0.596V

H003, MJ21193G, PNP, hfe = 86, Vbe = 0.615V

H004, MJ21194G, NPN, hfe = 53, Vbe = 0.603V

NPN power transistor S40443 from the right channel - shunt between the base and emitter

New ON Semiconductor power transistors - left and right channels

Pre & Tone Amplifier Board (PE01)

The pre & tone amplifier board must be removed from the chassis for servicing. I recommend removing the phono amplifier board and one bracket underneath it before attempting to free the pre & tone amplifier board. In addition, the metal shield under the pre & tone amplifier board needs to be removed to properly clean all the switches underneath.

The pre & tone amplifier board (PE01) is removed from the chassis

The pre & tone amplifier board has 6 solid tantalum capacitors (CE13, CE14, CE33, CE34, CE35, CE36) installed in the signal path, 2 bi-polar e-caps (CE37, CE38) installed in the output signal path, and 5 aluminum electrolytic capacitors (CE09, CE10, CE11, CE12, CE39).

Two original tantalum capacitors (CE33, CE34) with a rated capacitance of 1uF were replaced with film polyester WIMA caps. The other 4 tantalum e-caps were replaced with modern low leakage Nichicon UKL caps. Two bi-polar e-caps were replaced with new bi-polar Nichicon UES caps. And the remaining aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the pre & tone amplifier board:

CE09: rated capacitance – 100uF, measured – 117uF, ESR – 0.46Ω, deviation: +17%

CE10: rated capacitance – 100uF, measured – 131uF, ESR – 0.32Ω, deviation: +31%

CE11: rated capacitance – 10uF, measured – 13uF, ESR – 0.44Ω, deviation: +30%

CE12: rated capacitance – 10uF, measured – 12uF, ESR – 0.61Ω, deviation: +20%

CE13: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 1.68Ω, deviation: 0%

CE14: rated capacitance – 3.3uF, measured – 3.2F, ESR – 2.6Ω, deviation: -3%

CE33: rated capacitance – 1uF, measured – 1uF, ESR – 4.4Ω, deviation: 0%

CE34: rated capacitance – 1uF, measured – 1uF, ESR – 4.8Ω, deviation: 0%

CE35: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 2.0Ω, deviation: 0%

CE36: rated capacitance – 3.3uF, measured – 3.4uF, ESR – 2.3Ω, deviation: +3%

CE37: rated capacitance – 4.7uF, measured – 4.6uF, ESR – 1.55Ω, deviation: -2%

CE38: rated capacitance – 4.7uF, measured – 4.3uF, ESR – 2.1Ω, deviation: -9%

CE39: rated capacitance – 220uF, measured – 187uF, ESR – 0.09Ω, deviation: -15%

The failure-prone 2SA721 transistor installed in positions HE04 and HE06 was replaced with low-noise Fairchild KSA992 transistor. Also, the original 2SC1327 transistor installed in positions HE03 and HE05 was also replaced with low-noise Fairchild KSC1845 since it is complemented to 2SA721.

Pre and tone amplifier board - before and after

AM Tuner Board (P150)

The AM tuner board has one low leakage e-cap (C171) and 6 aluminum electrolytic capacitors (C167, C168, C169, C170, C172, C173).

The original low leakage e-cap was replaced with a film polyester WIMA cap. The remaining aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the AM tuner board:

C167: rated capacitance – 22uF, measured – 29uF, ESR – 0.51Ω, deviation: +32%

C168: rated capacitance – 100uF, measured – 121uF, ESR – 0.18Ω, deviation: +21%

C169: rated capacitance – 4.7uF, measured – 5.5uF, ESR – 1.46Ω, deviation: +17%

C170: rated capacitance – 100uF, measured – 124uF, ESR – 0.34Ω, deviation: +24%

C171: rated capacitance – 1uF, measured – 1uF, ESR – 2.3Ω, deviation: 0%

C172: rated capacitance – 100uF, measured – 123uF, ESR – 0.12Ω, deviation: +23%

C173: rated capacitance – 4.7uF, measured – 5.5uF, ESR – 1.34Ω, deviation: +17%

AM tuner board - before and after

Dolby FM Level Amplifier Board (PC01)

This board has only 4 solid tantalum capacitors: CC01, CC02, CC03, and CC04. I replaced them with film polyester WIMA caps.

Test results on original capacitors removed from the Dolby FM level amplifier board:

CC01: rated capacitance – 1uF, measured – 1uF, ESR – 4.3Ω, deviation: 0%

CC02: rated capacitance – 1uF, measured – 1uF, ESR – 5.9Ω, deviation: 0%

CC03: rated capacitance – 1uF, measured – 1uF, ESR – 5.0Ω, deviation: 0%

CC04: rated capacitance – 1uF, measured – 1uF, ESR – 5.4Ω, deviation: 0%

Dolby FM level amplifier board - before and after

MPX Stereo Decoding Amplifier Board (P300)

Well, this is the most challenging board for servicing in the Marantz 2275. This board cannot be completely released from the chassis without removing some wires from it. And I don't like the idea to cut any of the original wires unless absolutely necessary. So, I was able to rotate this board about 90 degrees (even less actually) to get to the back (foil) side for servicing after loosening some wires. But the many wires under this board and the very limited space make servicing this board a real challenge. So keep that in mind if you ever decide to service this board in Marantz 2275.

The MPX stereo decoding amplifier board has 3 bipolar electrolytic capacitors (C307, C308, C309), 4 solid tantalum e-caps C323, C324, C325, C326), and 11 aluminum electrolytic capacitors (C302, C304, C306, C327, C328, C329, C331, C332, C337, C338, C342.

The original bipolar and solid tantalum capacitors were replaced with film polyester WIMA and Kemet caps. Two ordinary aluminum e-caps with a rated capacitance of 1uF (C331, C338) were also replaced with film polyester WIMA caps. The remaining aluminum e-caps were replaced with low impedance Nichicon UPW/UPM caps.

Test results on original capacitors removed from the MPX stereo decoding amplifier board:

C302: rated capacitance – 33uF, measured – 46uF, ESR – 1.1Ω, deviation: +39%

C304: rated capacitance – 22uF, measured – 29uF, ESR – 0.66Ω, deviation: +32%

C306: rated capacitance – 22uF, measured – 29uF, ESR – 0.61Ω, deviation: +32%

C307: rated capacitance – 0.47uF, measured – 0.42uF, ESR – N/A, deviation: -11%

C308: rated capacitance – 0.22uF, measured – 0.31uF, ESR – N/A deviation: +41%

C309: rated capacitance – 0.22uF, measured – 0.28uF, ESR – N/A, deviation: +27%

C323: rated capacitance – 0.22uF, measured – 0.21uF, ESR – N/A, deviation: -5%

C324: rated capacitance – 0.22uF, measured – 0.22uF, ESR – N/A, deviation: 0%

C325: rated capacitance – 1uF, measured – 1uF, ESR – 7.3Ω, deviation: 0%

C326: rated capacitance – 1uF, measured – 1.1uF, ESR – 6.6Ω, deviation: +10%

C327: rated capacitance – 220uF, measured – 191uF, ESR – 0.11Ω, deviation: -13%

C328: rated capacitance – 220uF, measured – 230uF, ESR – 0.14Ω, deviation: +5%

C329: rated capacitance – 10uF, measured – 13uF, ESR – 1.49Ω, deviation: +30%

C331: rated capacitance – 1uF, measured – 1.1uF, ESR – 1.26Ω, deviation: +10%

C332: rated capacitance – 10uF, measured – 13uF, ESR – 1.74Ω, deviation: +30%

C337: rated capacitance – 4.7uF, measured – 5.2uF, ESR – 1.24Ω, deviation: +11%

C338: rated capacitance – 1uF, measured – 1.1uF, ESR – 1.52Ω, deviation: +10%

C342: rated capacitance – 10uF, measured – 13uF, ESR – 1.56Ω, deviation: +30%

MPX stereo decoding amplifier board - before and after

FM IF Amplifier Board (P200)

The FM IF amplifier board has one solid tantalum capacitor C256 and 14 aluminum electrolytic capacitors (C204, C205, C208, C218, C219, C229, C242, C243, C244, C245, C248, C249, C250, C261). 

Both the original tantalum capacitor C256 and ordinary aluminum e-cap C261 were replaced with a film polyester WIMA cap. The remaining e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the FM IF amplifier board:

C204: rated capacitance – 10uF, measured – 14uF, ESR – 1.21Ω, deviation: +40%

C205: rated capacitance – 10uF, measured – 13uF, ESR – 1.24Ω, deviation: +30%

C208: rated capacitance – 10uF, measured – 14uF, ESR – 1.16Ω, deviation: +40%

C218: rated capacitance – 10uF, measured – 13uF, ESR – 1.31Ω, deviation: +30%

C219: rated capacitance – 10uF, measured – 12uF, ESR – 1.02Ω, deviation: +20%

C229: rated capacitance – 10uF, measured – 14uF, ESR – 1.06Ω, deviation: +40%

C242: rated capacitance – 10uF, measured – 13uF, ESR – 1.15Ω, deviation: +30%

C243: rated capacitance – 100uF, measured – 133uF, ESR – 0.31Ω, deviation: +33%

C244: rated capacitance – 10uF, measured – 13uF, ESR – 1.05Ω, deviation: +30%

C245: rated capacitance – 10uF, measured – 13uF, ESR – 1.13Ω, deviation: +30%

C248: rated capacitance – 10uF, measured – 13uF, ESR – 1.04Ω, deviation: +30%

C249: rated capacitance – 100uF, measured – 129uF, ESR – 0.21Ω, deviation: +29%

C250: rated capacitance – 22uF, measured – 29uF, ESR – 0.48Ω, deviation: +32%

C256: rated capacitance – 1uF, measured – 1.1uF, ESR – 4.1Ω, deviation: +10%

C261: rated capacitance – 1uF, measured – 1.2uF, ESR – 1.31Ω, deviation: +20%

FM IF amplifier board - before and after

Dial, Meter, and Functional Lamps

Well, look at the picture below. Do you see something wrong? Yes, the plastic reflector behind the dial lamps has melted. That is why I always recommend replacing the original incandescent lamps in any vintage Marantz with warm white LED lamps. Incandescent lamps produce a lot of heat and eventually destroy the plastic reflector behind them. LED lamps produce much less heat, safe for plastic, and last almost forever. In addition, the color temperature of warm white LED lamps is very close to that of incandescent bulbs. All this makes LED lamps the best replacement for original incandescent bulbs in vintage receivers.

The plastic reflector behind the dial lamps - melted over time

I replaced the old incandescent bulbs with warm white LED lamps to maintain the original look and decrease heat. The original incandescent lamp behind the meter was also replaced with a warm white LED lamp. The old yellowish vellum behind the dial scale was replaced with new heavyweight vellum paper.

Two original functional lamps (FM and Stereo) in this unit burned out. I replaced them with new bi-pin lamps (8V/40mA).

The original dial pointer lamp was also burned out. I replaced it with a new incandescent lamp (8V/60mA, 4.7mm).

Dial scale removed - original incandescent dial lamps

Original vellum paper - color changed due to extreme heat

Dial scale removed - new LED lamps

New heavyweight vellum paper

Miscellaneous Issues

• The electrolytic capacitor C008 (33uF/10V) across meter leads was replaced with a new low impedance Nichicon UPW cap.
• The old dial string in this unit was loosened. I replaced it with a new dial cord (the most tedious job on any vintage receiver).

The e-cap C008 across meter leads - original and new

New dial cord

DC offset and Bias Adjustments

The DC offset is measured across speaker terminals on each channel. It should be adjusted as close to zero volts as possible with the trimming resistor R741.

Be aware, that the service manual has an error for bias adjustment. The correct procedure is described below.

The bias on each channel is measured across dual resistor R740. So, the DC voltmeter should be connected between pins J704 (+) and J703 (-). Then, the voltage should be adjusted to ~10mV on each channel with the trimming resistors R742. It corresponds to the idling current of 25mA.

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 receiver 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 27.10 VRMS (left channel) and 27.03 VRMS (right channel). It corresponds to the output power of 91.8W on the left channel and 91.3W on the right channel.

Output power test

As usual, all the knobs and the face plate 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 awesome, and the sound is clear and warm. Classic Marantz sound from the late 70's! Please watch a short demo video at the end of this post. Thank you for reading.

Marantz 2275 - after restoration

Demo video after repair & restoration