Marantz 2270 Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Marantz

Model: 2270

SN: 52380J4

Today I'm showcasing a Marantz 2270 vintage receiver that came in for restoration. This is one of the most famous and desirable receivers of all time. Marantz 2270 was manufactured from 1972 to 1974. It produces 70 watts per channel into 8 ohms with no more than 0.3% total harmonic distortion. The damping factor at 8 ohms is 45. The optional walnut veneer cabinet for this model is WC-22. The retail price in 1972 was $549.95 (Ref. High Fidelity, April 1972, page 35).

According to the factory stamp on the chassis, this receiver was manufactured in April 1976.

Regulated Power Supply and Protection Relay Board (P800)

The power supply board has 8 aluminum electrolytic capacitors: C801, C802, C803, C804, C805, C806, C807, and C810.

All e-caps except the C801 on this board were replaced with Nichicon UPW/UPM low-impedance capacitors. Capacitor C801 was replaced with a new Cornell Dubilier type 381LX capacitor. The new capacitor has the same diameter and lead spacing as the original.

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:

C801: rated capacitance – 470uF, measured – 528uF, ESR – 0.26Ω, deviation: +12%

C802: rated capacitance – 330uF, measured – 310uF, ESR – 0.56Ω, deviation: -6%

C803: rated capacitance – 470uF, measured – 435uF, ESR – 0.52Ω, deviation: -7%

C804: rated capacitance – 330uF, measured – 303uF, ESR – 0.57Ω, deviation: -8%

C805: rated capacitance – 3.3uF, measured – 3.7uF, ESR – 1.62Ω, deviation: +12%

C806: rated capacitance – 10uF, measured – 13uF, ESR – 0.72Ω, deviation: +30%

C807: rated capacitance – 220uF, measured – 252uF, ESR – 0.63Ω, deviation: +15%

C810: rated capacitance – 47uF, measured – 58uF, ESR – 0.83Ω, deviation: +23%

The S1B-01-02 diodes (H801, H802, H811, H812, H813) were upgraded to Fairchild UF4005 fast recovery rectifiers.

All transistors except the H803 and H805 were also replaced to improve the reliability of the power supply. Below is a list of original and replacement parts that I have used.

Q806: NPN, 2SC734 (original), replaced with a new Fairchild KSC2383YTA

Q808: NPN, 2SC945 (original), replaced with a new Fairchild KSC2383YTA

Q809: NPN, 2SC1213A (original), replaced with a new Fairchild KSC2383YTA

Q8010: NPN, 2SC1213A (original), replaced with a new Fairchild KSC2383YTA

The large wire-wound resistor R801 was replaced with a new IRC / TT Electronics wire-wound resistor. The new resistor is smaller, does not have bulky corners, and has a rated power of 7W instead of 5W.

The original trimming resistor R809 was 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 J802 and J803 (ground) was adjusted to +35.0V DC with trimming resistor R809.

Regulated power supply & protection relay circuit board - voltage regulator adjustment

Regulated power supply & protection relay circuit board - before and after

Tone Amplifier Board (P400)

The tone amplifier board has 8 solid tantalum capacitors (C403, C404, C407, C408, C410, C411, C414, C415) installed in the signal path and 3 aluminum electrolytic capacitors (C405, C406, C409) for local filtering.

All solid tantalum capacitors were replaced with high-quality WIMA film polyester caps. The remaining filtering capacitors were replaced with Nichicon UPW/UPM low-impedance capacitors. Note that the three original solid tantalum capacitors (C407, C410, and C411) have extremely high ESR resistance of over 20 ohms!

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

C403: rated capacitance – 1uF, measured – 1uF, ESR – 8.3Ω, deviation: 0%

C404: rated capacitance – 1uF, measured – 1uF, ESR – 5.4Ω, deviation: 0%

C405: rated capacitance – 10uF, measured – 11uF, ESR – 1.33Ω, deviation: +10%

C406: rated capacitance – 10uF, measured – 11uF, ESR – 1.56Ω, deviation: +10%

C407: rated capacitance – 3.3uF, measured – 3.8uF, ESR – 21.2Ω, deviation: +15%

C408: rated capacitance – 3.3uF, measured – 3.4uF, ESR – 1.68Ω, deviation: +3%

C409: rated capacitance – 100uF, measured – 106uF, ESR – 0.72Ω, deviation: +6%

C410: rated capacitance – 3.3uF, measured – 3.8uF, ESR – 24.4Ω, deviation: +15%

C411: rated capacitance – 3.3uF, measured – 4.2uF, ESR – 38.2Ω, deviation: +27%

C414: rated capacitance – 1uF, measured – 0.9uF, ESR – 2.4Ω, deviation: -10%

C415: rated capacitance – 1uF, measured – 0.9uF, ESR – 1.39Ω, deviation: -10%

Four NPN transistors (H401, H402, H405, H406) installed on this board are Toshiba 2SC1000. This transistor is on my list of transistors that are prone to failure. I replaced all the original 2SC1000s with new Fairchild KSC1845 transistors.

The PNP transistor 2SA493 installed in positions H403, H404, H407, and H408 is not on my list of prone-to-failure transistors but is a complementary pair to the 2SC1000. So, I replaced all the original 2SC493s with new Fairchild KSC992 transistors.

Tone amplifier board - before and after

Phono Amplifier Board (P700)

The phono amplifier board has 4 solid tantalum capacitors (C701, C702, C703, C704) and one aluminum electrolytic capacitor C713.

The original solid tantalum capacitors (C701 and C702) installed in the input signal path were replaced with Panasonic film polyester caps. The other two solid tantalum capacitors (C703 and C704) were replaced with modern low-leakage Nichicon UKL caps. The local filtering capacitor C713 was replaced with a Nichicon UPM low-impedance capacitor.

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

C701: rated capacitance – 2.2uF, measured – 2.3uF, ESR – 5.6Ω, deviation: +5%

C702: rated capacitance – 2.2uF, measured – 2.3uF, ESR – 3.6Ω, deviation: +5%

C703: rated capacitance – 22uF, measured – 23uF, ESR – 0.74Ω, deviation: +5%

C704: rated capacitance – 22uF, measured – 24uF, ESR – 1.19Ω, deviation: +9%

C713: rated capacitance – 100uF, measured – 111uF, ESR – 0.56Ω, deviation: +11%

The prone-to-failure transistors 2SC1000 (H701, H702, H703, H704) and 2SC458LG (H705, H706) installed on this board were replaced with low-noise Fairchild KSC1845 transistors.

Both 1S1212 epoxy diodes installed in positions H707 and H708 were replaced with 1N4148 diodes.

The original VD1212 dual diode installed in position H709 was replaced with two 1N4148 diodes connected in series.

Phono amplifier board - before and after

Power Amplifier Board (P750)

Marantz 2270 has two power amplifier boars. Each board is mounted directly on the heatsink with two power transistors.

The right channel on this unit was previously toasted and many of the original components were replaced:

• three carbon resistors (R776, R782, R786)
• one wire-wound emitter resistor (R788)
• two driver transistors (H758, H759)
• one driver transistor (H766)
• one output transistor (H003)

Power amplifier board from the right channel - before servicing (heatsink is removed)

The original R776 resistor with a nominal resistance of 30kΩ was previously replaced with two 1.5kΩ resistors connected in series. As a result, the total resistance of R776 became 3kΩ instead of 30kΩ! I replaced it with a new KOA Speer metal film resistor (30.1kΩ, 1/2W).

The R782 carbon resistor (previously replaced with a single 1.5kΩ resistor) was replaced with a new KOA Speer metal film resistor (1.5kΩ, 1/2W). 

The R786 carbon resistor (previously replaced by two 47 ohm resistors in series) has been replaced with a new KOA Speer carbon film flameproof resistor (100Ω, 1W).

The original wire-wound emitter resistor R788 with a nominal resistance of 0.2Ω was previously replaced with a wire-wound resistor with a nominal resistance of 0.33Ω. I don't know why a 0.33Ω resistor was chosen instead of a 0.2Ω resistor. I replaced both emitter resistors (R788, R789) with new Vishay wire-wound resistors (0.2Ω, 5W).

The two original driver transistors (H758/H759) were previously replaced with Sony 2SC895/2SA762 transistors (TO-66 package). These transistors are now obsolete and were most likely replaced in the late 80s or early 90s. I decided to leave them.

The original H760 bias stabilization transistor in each channel is Toshiba 2SC496. One of them has a low current gain of 31 (according to the database this parameter should be >70 for rank O). I replaced each 2SC496 with a new Fairchild MJE243G transistor.

Each power amplifier board has one solid tantalum capacitor C761 and two aluminum electrolytic capacitors (C759, C760).

The original solid tantalum capacitor was replaced with a low-leakage Nichicon UKL cap. The remaining aluminum e-caps were replaced with Nichicon UPW low-impedance capacitors.

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

left channel:

C759: rated capacitance – 10uF, measured – 12uF, ESR – 2.2Ω, deviation: +20%

C760: rated capacitance – 10uF, measured – 12uF, ESR – 2.4Ω, deviation: 20%

C761: rated capacitance – 22uF, measured – 24uF, ESR – 2.0Ω, deviation: +9%

right channel:

C759: rated capacitance – 10uF, measured – 12uF, ESR – 2.1Ω, deviation: +20%

C760: rated capacitance – 10uF, measured – 13uF, ESR – 2.4Ω, deviation: +30%

C761: rated capacitance – 22uF, measured – 25uF, ESR – 2.2Ω, deviation: +14%

The first stage of the power amplifier circuit is a differential amplifier consisting of two amplifying transistors with a common emitter: H751/H752. The original PNP transistor installed in these positions is 2SA640. This transistor is not on my list of infamous transistors prone to failure. However, testing each pair of transistors installed in the differential amplifier always makes sense to ensure they are still well-matched.

As can be seen from the test below, the mismatch of each pair of original transistors in the left and right channels is still very small: ~3% (left channel) and ~1% (right channel). However, I decided to replace each pair of the original 2SA640s with a closely matched pair (within 1%) of modern Fairchild KSA992 low-noise transistors to improve the reliability of the differential amplifier. I put a slight smear of new thermal paste on one face of KSA992 and pressed both transistors together. Heat shrink tubing was used to hold them together mechanically.

Test results on original 2SA640 transistors

H751 (left channel): hfe - 368, Vbe - 0.744V 

H752 (left channel): hfe - 356, Vbe - 0.748V

H751 (right channel): hfe - 364, Vbe - 0.757V 

H752 (right channel): hfe - 368, Vbe - 0.757V

Test results on new KSA992FBU transistors

H751 (left channel): hfe - 423, Vbe - 0.761V

H752 (left channel): hfe - 423, Vbe - 0.761V

H751 (right channel): hfe - 426, Vbe - 0.760V

H752 (right channel): hfe - 427, Vbe - 0.762V 

Power amplifier board from the left channel - before and after servicing

Power amplifier board from the right channel - before and after servicing

Power Transistors

All original power transistors were removed, degreased, and tested with Atlas DCA55 semiconductor analyzer. Each transistor passed the test, but one from the left channel has a relatively low current gain of ~27. Also, as I mentioned before, the original Fairchild transistor H003 from the right channel was previously replaced with a Motorola SJ2518 transistor.

Because of all these issues, 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 = 133, Vbe = 0.588V

H002, S40443, NPN, hfe = 27, Vbe = 0.545V

H003, SJ2518, PNP, hfe = 138, Vbe = 0.561V

H004, S40443, NPN, hfe = 41, Vbe = 0.552V

Test results on new ON Semiconductor power transistors:

H001, MJ21193G, PNP, hfe = 85, Vbe = 0.608V

H002, MJ21194G, NPN, hfe = 54, Vbe = 0.595V

H003, MJ21193G, PNP, hfe = 84, Vbe = 0.611V

H004, MJ21194G, NPN, hfe = 54, Vbe = 0.601V

Original power transistors - left and right channels

New ON Semiconductor power transistors - left and right channels

Dial, Meter, and Functional Lamps

The old incandescent bulbs were replaced with warm white LED lamps to maintain the original look and decrease heat. The original incandescent lamp behind the meter was replaced with a light blue LED lamp to match the illumination of the dial scale. The old yellowish vellum behind the dial scale was replaced with new heavyweight vellum paper.

The original functional lamps (Stereo, Phono 2, and Tape) in this unit have 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).

Main Power Switch Replacement

The main power switch on this unit tends to get stuck in the ON position. I removed the front panel to see if the switch cover was rubbing against the plastic insert, but it was not. The problem was with the worn power switch. So, I decided to replace it with a new switch and snubber. 

Main power switch - original and new

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 R762.

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 resistors R788 and R789. The DC voltmeter should be connected between pins J754 (+) and J760 (-). Then, the voltage should be adjusted to ~10mV on each channel with the trimming resistor R763. 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 25.61 VRMS (left channel) and 25.66 VRMS (right channel). It corresponds to the output power of 82.0W on the left channel and 82.3W 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 sounds great! Please watch a short demo video at the end of this post. Thank you for reading.

Marantz 2270 - after restoration

Demo video after repair & restoration

Marantz 2220B Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Marantz

Model: 2220B

SN: 31995J4

Today I'm showcasing a Marantz 2220B vintage receiver that came in for restoration. Marantz 2220B was manufactured from 1974 to 1977. It produces 20 watts per channel into 8 ohms with no more than 0.5% total harmonic distortion. The damping factor at 8 ohms is 20. The optional walnut veneer cabinet for this model is WC-122 or WC-22. 

Marantz 2220B is a service-friendly receiver because of excellent access to each PCB.

FM Tuner Section Troubleshooting

Initial evaluation of this unit revealed that in addition to the common problems found in almost all vintage gears such as scratchy/noisy controls, burned bulbs, intermittent sound, etc., this unit also has issues with FM stereo reception. Despite a strong signal from the local stations, the stereo indicator lamp doesn't light up. I checked the sound with my headphones but didn't notice the stereo separation either. Also, pressing the FM Muting switch would mute the sound completely, even when tuned to a station with a strong signal.

The first thing I did was check the stereo indicator lamp. The stereo lamp lights up when the Phono, Tape, or Aux input is selected. However, it turns off when switching to FM input. This means that the lamp has not burned out.

The second step was to test the stereo MPX decoding circuit. I connected a frequency counter to the R312 test point and checked for the 19kHz VCO output. It was slightly off at ~18.8kHz and I adjusted it exactly to 19.0kHz with the trimmer R304. It didn't change anything. The sound was clear and loud, but still only in mono.

The next logical step was to check the FM Front End tuner alignment. A quick test at 87 MHz and 109 MHz revealed no problems. 

I then cleaned up all the controls, paying particular attention to the FM Muting switch, and moved on to the FM IF amplifier board. I checked all voltage distributions on this board and compared them with those shown in the circuit diagram. At no signal condition, the measured voltage on each transistor was very close to that shown in the circuit diagram. However, when I applied a stereo signal, the measured voltage across the three transistors (H207, H208, and H209) did not match what was shown in the circuit diagram (see below).

Voltage distributions at no signal condition (ref. voltage from the schematic are in brackets):

H201: B - 3.3V (3.4V); C - 7.5V (7.7V); E - 2.6V (2.8V)

H202: B - 3.3V (3.5V); C - 7.7V (8.5V); E - 2.7V (2.8V)

H203: B - 3.0V (3.0V); C - 9.1V (9.4V); E - 2.4V (2.4V)

H204: B - 3.2V (3.3V); C - 9.6V (10.1V); E - 2.5V (2.7V)

H205: B - 2.4V (3.3V); C - 13.3V (13.6V); E - 2.0V (2.8V)

H206: B - 3.5V (3.7V); C - 12.2V (13.2V); E - 2.8V (3.0V)

H207: B - 0V (0.04V); C - 13.9V (14.3V); E - 0.05V (0.06V)

H208: B - 0.05V (N/A); C - 0.18V (0.27V); E - 0V (0V)

H209: B - 0V (0.02V); C - 7.3V (7.4V); E - 0V (0V)

Voltage distributions when the stereo signal is applied:

H201: the same as at no signal condition

H202: the same as at no signal condition

H203: the same as at no signal condition

H204: the same as at no signal condition

H205: the same as at no signal condition

H206: the same as at no signal condition

H207: B - 0.07V (1.77V); C - 13.9V (14.3V); E - 0.08V (1.18V)

H208: B - 0.08V (N/A); C - 0.2V (0.06V); E - 0V (0V)

H209: B - 0.08V (0.6V); C - 7.3V (0.06V); E - 0V (0V)

The DC voltage obtained by rectifying the sub IF output signal from the H206 is applied to the base of H207. The output signal must be above a specified level to turn on transistor H207. This level (muting threshold level) is adjusted by trimmer R253. 

When the H207 turns on, the muting switch transistor H208 is also turned on. It decreases the emitter-collector resistance and allows the emitter current path to the final IF amplifier H205. However, if the DC output obtained is smaller than the predetermined level, the H207 keeps its turn-off state. As a result, the switch transistor H208 also keeps its turn-off state and no emitter current is supplied to the transistor H205. The DC voltage obtained is also used to make the Auto-Stereo switching transistor H209 turn on and off.

So, the problem seems to be somewhere down in the circuit after transistor H206. The voltage measured on the base, collector, and emitter of H206 matches those on the circuit diagram. However, the DC voltage applied to the base of H207 is too small to turn it on. 

I tested the transistor H207 to make sure that it was okay. Then, I measured the voltage at the base of H207 while rotating the trimmer R253. The base voltage was very low (~0.05-0.07V) at any position of the trimming resistor. I thought that perhaps one of the 1N60 germanium diodes was faulty, but testing did not confirm this assumption. Finally, I checked the voltage on the anode of H217, and it was close to zero volts.

So, the faulty component appears to be the coil L202. I swapped the suspect L202 with a spare coil from another Marantz 2220B and the stereo reception was restored. Now, the voltage at the anode H217 is 1.4V, the stereo indicator lamp lights up, and I can hear the stereo separation between the left and right channels. I double-checked the voltage across the three transistors (H207, H208, and H209) and it is also very close to that shown in the circuit diagram.

Voltage distributions after the faulty coil L202 was replaced (stereo signal is applied):

H207: B - 1.56V (1.77V); C - 13.8V (14.3V); E - 0.95V (1.18V)

H208: B - 0.68V (N/A); C - 0.08V (0.06V); E - 0V (0V)

H209: B - 0.6V (0.6V); C - 0.05V (0.06V); E - 0V (0V)

Power Supply Board (P800)

The regulated power supply has 6 aluminum e-caps C803, C804, C805, C808, C809, and C810. All of them were replaced with low-impedance and high-reliability Nichicon UPW caps. Those e-caps are designed for switching power supplies and can operate in the temperature range from -55 to +105 C. The original e-caps installed in vintage gears from the 70s have a maximum operating temperature of +85C.

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

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

C803: rated capacitance – 470uF, measured – 448uF, ESR – 0.29Ω, deviation: -5%

C804: rated capacitance – 470uF, measured – 306uF, ESR – 0.44Ω, deviation: -35%

C805: rated capacitance – 100uF, measured – 93uF, ESR – 1.68Ω, deviation: -7%

C808: rated capacitance – 3.3uF, measured – open

C809: rated capacitance – 470uF, measured – 519uF, ESR – 0.52Ω, deviation: +10%

C810: rated capacitance – 1000uF, measured – 1166uF, ESR – 1.52Ω, deviation: +17%

Both transistors (H805 & H806) and one rectifier diode H808 installed on this board were also replaced to improve the reliability of the power supply. The original transistor 2SD330 installed in position H805 was replaced with a new ON Semiconductor MJE15030G. Transistor 2SC945 installed in position H806 was replaced with a new Fairchild KSC945CYTA. The rectifier diode SIB-01-02 installed in position H808 was upgraded to a fast recovery rectifier UF4005.

The original trimming resistor R808 was replaced with a new Bourns potentiometer.

The DC voltage between pin J812 and ground was adjusted to +35V with the trimming resistor R808.

DC voltage between pin J812 and ground under no signal condition

Power supply board - before and after

Phono Amplifier Board (P400)

The phono amplifier board has two solid tantalum capacitors (C401, C402), two low leakage e-caps (C407, C408), and three aluminum electrolytic capacitors (C411, C412, C421). The solid tantalum capacitors installed in the signal path were replaced with modern low-leakage Nichicon UKL caps. The original low-leakage capacitors were also 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 phono amplifier board:

C401: rated capacitance – 2.2uF, measured – 2.2uF, ESR – 6.8Ω, deviation: 0%

C402: rated capacitance – 2.2uF, measured – 2.2uF, ESR – 6.4Ω, deviation: 0%

C407: rated capacitance – 22uF, measured – 22uF, ESR – 0.71Ω, deviation: 0%

C408: rated capacitance – 22uF, measured – 21uF, ESR – 0.88Ω, deviation: -5%

C411: rated capacitance – 47uF, measured – 56uF, ESR – 1.61Ω, deviation: +19%

C412: rated capacitance – 47uF, measured – 55uF, ESR – 1.14Ω, deviation: +17%

C421: rated capacitance – 100uF, measured – 102uF, ESR – 1.05Ω, deviation: +2%

Phono amplifier board - before and after

Tone Amplifier Board (PE01)

The tone amplifier board has six low leakage e-caps (CE05, CE06, CE19, CE20, CE21, CE22), two bi-polar capacitors (CE23, CE24), and three aluminum e-caps (CE03, CE04, CE25). The original low-leakage e-caps CE19 and CE20 were replaced with film polyester WIMA caps. The other low leakage e-caps with higher rated capacitance were replaced with modern low leakage Nichicon UKL caps. Two bi-polar e-caps were replaced with film polyester WIMA caps. And, the remaining aluminum e-caps were replaced with low-impedance Nichicon UPW caps.

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

CE03: rated capacitance – 10uF, measured – 11uF, ESR – 1.61Ω, deviation: +10%

CE04: rated capacitance – 10uF, measured – 9uF, ESR – 1.44Ω, deviation: -10%

CE05: rated capacitance – 4.7uF, measured – 4.4uF, ESR – 2.6Ω, deviation: -6%

CE06: rated capacitance – 4.7uF, measured – 4.7uF, ESR – 2.8Ω, deviation: 0%

CE19: rated capacitance – 1uF, measured – 1uF, ESR – 4.2Ω, deviation: 0%

CE20: rated capacitance – 1uF, measured – 1uF, ESR – 4.4Ω, deviation: 0%

CE21: rated capacitance – 3.3uF, measured – 2.9uF, ESR – 2.8Ω, deviation: -12%

CE22: rated capacitance – 3.3uF, measured – 3.1uF, ESR – 3.2Ω, deviation: -6%

CE23: rated capacitance – 1uF, measured – 0.8uF, ESR – 3.3Ω, deviation: -20%

CE24: rated capacitance – 1uF, measured – 0.8uF, ESR – 3.8Ω, deviation: -20%

CE25: rated capacitance – 220uF, measured – 181uF, ESR – 0.43Ω, deviation: -18%

Tone amplifier board - before and after

Main Amplifier Board (P700)

The main amplifier board has 4 low-leakage capacitors (C701, C702, C705, C706) and 4 aluminum electrolytic capacitors (C709, C710, C719, C720). I replaced the original low-leakage e-caps with modern low-leakage Nichicon UKL caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW caps.

The protection circuit is also assembled on this board and has 2 aluminum electrolytic capacitors C721 and C722. I replaced them with low-impedance Nichicon UPW caps.

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

C701: rated capacitance – 3.3uF, measured – 3.1uF, ESR – 6.1Ω, deviation: -6%

C702: rated capacitance – 3.3uF, measured – 3.1uF, ESR – 5.2Ω, deviation: -6%

C705: rated capacitance – 47uF, measured – 46uF, ESR – 1.04Ω, deviation: -2%

C706: rated capacitance – 47uF, measured – 46uF, ESR – 0.96Ω, deviation: -2%

C709: rated capacitance – 47uF, measured – 50uF, ESR – 0.98Ω, deviation: +6%

C710: rated capacitance – 47uF, measured – 53uF, ESR – 1.09Ω, deviation: +13%

C719: rated capacitance – 220uF, measured – 242uF, ESR – 0.91Ω, deviation: +10%

C720: rated capacitance – 10uF, measured – 11uF, ESR – 5.6Ω, deviation: +10%

C721: rated capacitance – 47uF, measured – 54uF, ESR – 1.08Ω, deviation: +15%

C722: rated capacitance – 220uF, measured – 245uF, ESR – 0.84Ω, deviation: +11%

The first stage of the main amplifier circuit is a differential amplifier consisting of two amplifying transistors with a common emitter: H701/H703 and H702/H704. The original PNP transistor installed in these positions is 2SA763. This transistor is not on my list of infamous transistors that are prone to failure. However, testing each pair of transistors installed in the differential amplifier always makes sense to ensure they are still well-matched. 

As can be seen from the test below, the mismatch of each pair of original transistors in the left and right channels is ~45% and ~13%, respectively. I prefer to keep the mismatch between the two transistors in a differential amplifier as small as possible since it is critical to the correct operation of this circuit. So, I replaced each pair of the original 2SA763s with a closely matched pair (within 1%) of modern Fairchild KSA992 low-noise transistors.

Test results on original 2SA763 transistors

H701 (left channel): hfe - 161, Vbe - 0.744V 

H703 (left channel): hfe - 234, Vbe - 0.754V

H702 (right channel): hfe - 202, Vbe - 0.748V 

H704 (right channel): hfe - 228, Vbe - 0.751V

Test results on new KSA992FBU transistors

H701 (left channel): hfe - 419, Vbe - 0.760V

H703 (left channel): hfe - 422, Vbe - 0.761V

H702 (right channel): hfe - 417, Vbe - 0.762V

H704 (right channel): hfe - 417, Vbe - 0.763V

The original relay driver transistor on this board is 2SC1318. It usually degrades over time and I replaced it with a new Fairchild KSC2383. The new transistor has the same pinout as the original one.

Each original MV-13 diode installed in positions H705 and H706 was replaced with two 1N4148 diodes connected in series.

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

Power amplifier board - before and after

Dolby FM Set (PC01)

The Dolby FM set has four 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 set:

CC01: rated capacitance – 1uF, measured – 1uF, ESR – 10.6Ω, deviation: 0%

CC02: rated capacitance – 1uF, measured – 1uF, ESR – 19.7Ω, deviation: 0%

CC03: rated capacitance – 1uF, measured – 1uF, ESR – 9.6Ω, deviation: 0%

CC04: rated capacitance – 1uF, measured – 1uF, ESR – 15.3Ω, deviation: 0%

Dolby FM set - before and after

FM IF Amplifier, Detector, Muting Control Board (P200)

The FM IF amplifier control board has 7 aluminum electrolytic capacitors: C218, C223, C224, C226, C231, C232, and C233. 

The original e-cap C231 was 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 control board:

C218: rated capacitance – 10uF, measured – 12uF, ESR – 2.8Ω, deviation: +20%

C223: rated capacitance – 10uF, measured – 11uF, ESR – 4.6Ω, deviation: +10%

C224: rated capacitance – 10uF, measured – 11uF, ESR – 4.1Ω, deviation: +10%

C226: rated capacitance – 100uF, measured – 116F, ESR – 1.28Ω, deviation: +16%

C231: rated capacitance – 1uF, measured – 1.1uF, ESR – 3.8Ω, deviation: +10%

C232: rated capacitance – 33uF, measured – 38uF, ESR – 1.22Ω, deviation: +15%

C233: rated capacitance – 10uF, measured – 9uF, ESR – 3.4Ω, deviation: -10%

The faulty coil L202 was replaced with a spare coil from another FM IF amplifier board.

FM IF amplifier, detector, muting control board - before and after

MPX Stereo Decoding Amplifier Board (P300)

The MPX Stereo decoding amplifier board has 3 bi-polar electrolytic capacitors (C305, C306, C307), 4 solid tantalum capacitors (C321, C322, C323, C324), and 3 aluminum electrolytic capacitors (C301, C308, C325).

All original bi-polar and solid tantalum capacitors were replaced with film polyester WIMA and Kemet caps. The remaining aluminum electrolytic capacitors were replaced with low-impedance Nichicon UPW caps. 

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

C301: rated capacitance – 10uF, measured – 12uF, ESR – 3.1Ω, deviation: +20%

C305: rated capacitance – 0.47uF, measured – 0.38uF, ESR – N/A, deviation: -19%

C306: rated capacitance – 0.22uF, measured – 0.16uF, ESR – N/A, deviation: -27%

C307: rated capacitance – 0.22uF, measured – 0.16uF, ESR – N/A, deviation: -27%

C308: rated capacitance – 220uF, measured – 270uF, ESR – 0.98Ω, deviation: +23%

C321: rated capacitance – 0.22uF, measured – 0.21uF, ESR – N/A, deviation: -5%

C322: rated capacitance – 0.22uF, measured – 0.22uF, ESR – N/A, deviation: 0%

C323: rated capacitance – 1uF, measured – 1uF, ESR – 5.6Ω, deviation: 0%

C324: rated capacitance – 1uF, measured – 1uF, ESR – 5.1Ω, deviation: 0%

C325: rated capacitance – 220uF, measured – 201uF, ESR – 0.56Ω, deviation: -9%

MPX Stereo decoding amplifier board - before and after

FM Front End & AM Tuner Board (P100)

The FM Front End & AM tuner board has one solid tantalum capacitor C141 and 5 aluminum electrolytic capacitors (C127, C135, C136, C140, C143).

The original solid tantalum capacitor was replaced with a film polyester Kemet cap. The other two capacitors with a nominal capacitance of 1uF were replaced with film polyester WIMA caps. The remaining aluminum electrolytic capacitors were replaced with low-impedance Nichicon UPW caps.

Test results on original capacitors removed from the FM Front End & AM tuner board:

C127: rated capacitance – 47uF, measured – 57uF, ESR – 0.74Ω, deviation: +21%

C135: rated capacitance – 10uF, measured – 13uF, ESR – 1.57Ω, deviation: +30%

C136: rated capacitance – 1uF, measured – 1.1uF, ESR – 1.75Ω, deviation: +10%

C140: rated capacitance – 100uF, measured – 109uF, ESR – 0.82Ω, deviation: +9%

C141: rated capacitance – 0.22uF, measured – 0.22uF, ESR – N/A, deviation: 0%

C143: rated capacitance – 1uF, measured – 0.9uF, ESR – 3.4Ω, deviation: -10%

FM Front End & AM tuner board after servicing (sorry, I forgot to take a picture before servicing)

Power Transistors

The original power transistors were removed, degreased, and tested with Atlas DCA55 semiconductor analyzer. According to the datasheet, the measured DC current gain on all transistors was in spec. 

However, it should be noted that the Atlas DCA55 semiconductor analyzer provides the accurate reading for DC current gain only on low-power transistors. A high-power transistor requires a much higher collector current and collector-emitter voltage to accurately measure its current gain. However, it is still a very useful device for comparing transistors of a similar type for the purposes of gain matching or fault-finding.

I applied fresh thermal paste and replaced the old thermal pads with new Mica ones, which is always a good idea when working with any vintage receiver. The old grease can frequently dry, causing the transistors to suffer from poor heat dissipation. This can lead to overheating and failure of the device.

Dial and Meter Lamps

The original dial and meter lamps in this unit were replaced with new warm white LED lamps.

DC offset and Bias Adjustments

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

The Bias on the left channel is measured across two emitter resistors R759 and R761. So, the voltmeter should be connected between J714 (+) and J716 (-). On the right channel, the bias is measured across two emitter resistors R760 and R762. So, the voltmeter should be connected between J715 (+) and J717 (-). The Bias should be adjusted to ~20mV on each channel with the trimming resistors R733 and R734.

The DC offset on the left channel is measured between J723 and J722 (ground). On the right channel, it is measured between J724 and J722 (ground). The DC offset should be adjusted as close to zero volts as possible with the trimming resistors R711 and R712.

Bias on the left and right channels after restoration

DC offset 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 13.71 VRMS (left channel) and 13.67 VRMS (right channel). It corresponds to the output power of 23.5W on the left channel and 23.4W 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 and sounds great again. Please watch a short demo video at the end of this post. Thank you for reading.

Marantz 2220B - after restoration

Demo video after repair & restoration