Marantz 4230 Receiver Restoration

Unit: AM/FM Stereo 2 + Quadradial 4 Receiver

Manufacturer: Marantz

Model: 4230

SN: 14880

Today I'm showcasing a Marantz 4230 vintage receiver that came in for restoration. The Marantz 4230 is a 4-channel quadraphonic receiver. It was introduced in 1973 and was on the market until 1978. It produces 30 watts per channel in stereo mode or 12 watts per channel in quadraphonic mode. The total harmonic distortion is less than 0.9%. The list price in 1974 was $499.95. The optional walnut veneer cabinet for this model is WC-22 and it was available for $29.95 (Ref. TEAM Electronics catalog, page 15).

The Power Mode switch on the rear panel switches the receiver from 4-channel mode to 2-channel mode. Be aware not to use 4Ω speakers in 2-channel mode! The 4Ω speakers can be only used in 4-channel mode. Use only 8Ω speakers (or higher) in 2-channel mode. Also, be sure to never cycle the rear panel Power Mode switch with the unit turned on.

According to the factory stamp on the chassis, this unit was manufactured in December 1973.

Power Supply Board (P800)

The regulated power supply board provides +35V DC to all of the amplifiers (except main power amplifiers), and +14V DC to the tuner section. 

This board has 5 aluminum electrolytic capacitors: C801, C802, C803, C804, and C805. I replaced them with high reliability, low impedance Nichicon UPW/UPM caps.

The original e-caps were tested with an Atlas ESR70 capacitance meter, and the results are below. Note, that one capacitor C801 failed the test (open circuit/low capacitance).

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

C801: rated capacitance – 3.3uF, measured – open circuit/low capacitance

C802: rated capacitance – 470uF, measured – 553uF, ESR – 0.11Ω, deviation: +18%

C803: rated capacitance – 330uF, measured – 405uF, ESR – 0.16Ω, deviation: +23%

C804: rated capacitance – 330uF, measured – 353uF, ESR – 0.06Ω, deviation: +7%

C805: rated capacitance – 470uF, measured – 498uF, ESR – 0.11Ω, deviation: +6%

I also replaced two original 2SC945 transistors installed in positions H802 and H803 with new Fairchild KSC945s.

After the servicing, the voltage between pin J801 and J811 (ground) was adjusted to +35.0V DC with trimming resistor R801.

Power supply board - voltage regulator adjustment

Power supply board - before and after

Power Amplifier Board (P700 x 2)

Marantz 4230 has two power amplifier boards: front (left & right channels) and rear (left & right channels). Each board has 2 low leakage e-caps (C703, C704), 11 aluminum electrolytic capacitors (C702, C707, C708, C712, C713, C716, C717, C718, C719, C720, C721), and 2 coupling capacitors (C726, C727). The original low leakage e-caps were replaced with high-quality film polyester WIMA caps. The original coupling capacitors were replaced with Nichicon LKG caps (type II, Gold Tune).  The new coupling capacitors are designed for high grade audio equipment, giving priority to high-fidelity sound quality. They have the same diameter and lead spacing but are shorter than the original ones. The remaining aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Note, that one capacitor C712 installed in the front board (left channel) failed the test (open circuit/low capacitance).

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

Front (left & right channels):

C702: rated capacitance – 47uF, measured – 54uF, ESR – 0.19Ω, deviation: +15%

C703: rated capacitance – 1uF, measured – 0.9uF, ESR – 4.5Ω, deviation: -10%

C704: rated capacitance – 1uF, measured – 1uF, ESR – 3.1Ω, deviation: 0%

C707: rated capacitance – 47uF, measured – 56uF, ESR – 0.11Ω, deviation: +19%

C708: rated capacitance – 47uF, measured – 56uF, ESR – 0.15Ω, deviation: +19%

C712: rated capacitance – 10uF, measured – open circuit/low capacitance

C713: rated capacitance – 10uF, measured – 11uF, ESR – 2.9Ω, deviation: +10%

C716: rated capacitance – 100uF, measured – 132uF, ESR – 0.32Ω, deviation: +32%

C717: rated capacitance – 100uF, measured – 128uF, ESR – 0.37Ω, deviation: +28%

C718: rated capacitance – 47uF, measured – 53uF, ESR – 1.88Ω, deviation: +13%

C719: rated capacitance – 47uF, measured – 54uF, ESR – 0.16Ω, deviation: +15%

C720: rated capacitance – 22uF, measured – 25uF, ESR – 0.38Ω, deviation: +14%

C721: rated capacitance – 22uF, measured – 25uF, ESR – 0.26Ω, deviation: +14%

C726: rated capacitance – 3300uF, measured – 3932uF, ESR – 0.03Ω, deviation: +19%

C727: rated capacitance – 3300uF, measured – 3886uF, ESR – 0.02Ω, deviation: +18%

Rear (left & right channels):

C702: rated capacitance – 47uF, measured – 53uF, ESR – 0.34Ω, deviation: +13%

C703: rated capacitance – 1uF, measured – 0.9uF, ESR – 3.9Ω, deviation: -10%

C704: rated capacitance – 1uF, measured – 0.9uF, ESR – 4.1Ω, deviation: -10%

C707: rated capacitance – 47uF, measured – 54uF, ESR – 0.15Ω, deviation: +15%

C708: rated capacitance – 47uF, measured – 56uF, ESR – 0.18Ω, deviation: +19%

C712: rated capacitance – 10uF, measured – 12uF, ESR – 2.1Ω, deviation: +20%

C713: rated capacitance – 10uF, measured – 11uF, ESR – 2.2Ω, deviation: +10%

C716: rated capacitance – 100uF, measured – 94uF, ESR – 0.66Ω, deviation: -6%

C717: rated capacitance – 100uF, measured – 123uF, ESR – 0.46Ω, deviation: +23%

C718: rated capacitance – 47uF, measured – 54uF, ESR – 1.11Ω, deviation: +15%

C719: rated capacitance – 47uF, measured – 46uF, ESR – 0.15Ω, deviation: -2%

C720: rated capacitance – 22uF, measured – 25uF, ESR – 1.91Ω, deviation: +14%

C721: rated capacitance – 22uF, measured – 25uF, ESR – 0.58Ω, deviation: +14%

C726: rated capacitance – 3300uF, measured – 3880uF, ESR – 0.04Ω, deviation: +18%

C727: rated capacitance – 3300uF, measured – 3826uF, ESR – 0.06Ω, deviation: +16%

Two driver transistors (H704 and H705) installed on the power amplifier board are Panasonic 2SC1318. This transistor is on my list of transistors that are prone to failure. I replaced each 2SC1318 with a modern Fairchild KSC2383. Note, that the original 2SC1318 transistor installed in position H705 (rear board, right channel) was toasted. It is still functional, but the measured current gain is only ~66, below the minimum value for this rank (rank Q, hfe = 85~170).

Toasted transistor 2SC1318 installed in position H705 (rear board, right channel)

Power amplifier board (front) - before and after

Power amplifier board (rear) - before and after

Power Transistors

According to the owner, this unit was serviced at a local repair shop around 1986-88. They replaced four of the original eight power transistors. The original power transistors installed in this unit are 2SC789 (package type TO-220) and the new transistors are 2SD315 (package type TO-66). Both transistors have similar parameters and are designed for use in audio frequency power amplifiers. In addition, the 2SD315 was officially recommended by Marantz as a replacement for the 2SC789 transistor (see Marantz Service Bulletin M-4230-3, August 19, 1975). So there are no questions here. However, using the same power transistors in both channels makes sense to ensure the same performance. So, I decided to replace all power transistors (H001 thru H004) with new OnSemi TIP41C transistors. The TIP41C transistor is designed for use in general-purpose amplifiers and has superior performance over the 2SC789 and 2SD315.

Power transistors (front) - before and after

Power transistors (rear) - before and after

Tone Amplifier Board (PE01)

The tone amplifier board has 20 low leakage e-caps (CE01, CE02, CE03, CE04, CE05, CE06, CE07, CE08, CE09, CE10, CE11, CE12, CE17, CE18, CE19, CE20, CE25, CE26, CE27, CE28) installed in the signal path and 5 aluminum electrolytic capacitors (CE13, CE14, CE15, CE16, CE29). The original low leakage e-caps with a rated capacitance of 1uF and lower were replaced with film polyester WIMA caps. The other 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 amplifier board:

CE01: rated capacitance – 4.7uF, measured – 4.6uF, ESR – 2.1Ω, deviation: -2%

CE02: rated capacitance – 4.7uF, measured – 4.7uF, ESR – 1.86Ω, deviation: 0%

CE03: rated capacitance – 4.7uF, measured – 4.6uF, ESR – 2.1Ω, deviation: -2%

CE04: rated capacitance – 4.7uF, measured – 4.5uF, ESR – 1.77Ω, deviation: -4%

CE05: rated capacitance – 0.47uF, measured – 0.42uF, ESR – N/A, deviation: -11%

CE06: rated capacitance – 0.47uF, measured – 0.43uF, ESR – N/A, deviation: -9%

CE07: rated capacitance – 0.47uF, measured – 0.43uF, ESR – N/A, deviation: -9%

CE08: rated capacitance – 0.47uF, measured – 0.46uF, ESR – N/A, deviation: -2%

CE09: rated capacitance – 1uF, measured – 1.1uF, ESR – 3.6Ω, deviation: +10%

CE10: rated capacitance – 1uF, measured – 1.1uF, ESR – 3.1Ω, deviation: +10%

CE11: rated capacitance – 1uF, measured – 1.1uF, ESR – 2.7Ω, deviation: +10%

CE12: rated capacitance – 1uF, measured – 1.0uF, ESR – 2.7Ω, deviation: 0%

CE13: rated capacitance – 10uF, measured – 13uF, ESR – 0.58Ω, deviation: +30%

CE14: rated capacitance – 10uF, measured – 13uF, ESR – 0.62Ω, deviation: +30%

CE15: rated capacitance – 10uF, measured – 13uF, ESR – 0.73Ω, deviation: +30%

CE16: rated capacitance – 10uF, measured – 13uF, ESR – 0.59Ω, deviation: +30%

CE17: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 1.73Ω, deviation: 0%

CE18: rated capacitance – 3.3uF, measured – 3.2uF, ESR – 1.26Ω, deviation: -3%

CE19: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 1.63Ω, deviation: 0%

CE20: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 1.67Ω, deviation: 0%

CE25: rated capacitance – 1uF, measured – 1.0uF, ESR – 3.8Ω, deviation: 0%

CE26: rated capacitance – 1uF, measured – 1.1uF, ESR – 2.8Ω, deviation: +10%

CE27: rated capacitance – 1uF, measured – 1.1uF, ESR – 2.6Ω, deviation: +10%

CE28: rated capacitance – 1uF, measured – 1.1uF, ESR – 2.8Ω, deviation: +10%

CE29: rated capacitance – 100uF, measured – 113uF, ESR – 0.08Ω, deviation: +13%

Tone amplifier board - before and after

Vari-Matrix Unit (P500)

The vari-matrix unit has 10 low leakage e-caps (C501, C502, C503, C504, C505, C506, C511, C512, C515, C516) installed in the signal path and 3 aluminum electrolytic capacitors (C513, C514, C521). The original low leakage e-caps with a rated capacitance of 0.47uF were replaced with film polyester WIMA caps. The other 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 vari-matrix unit:

C501: rated capacitance – 0.47uF, measured – 0.41uF, ESR – N/A, deviation: -13%

C502: rated capacitance – 0.47uF, measured – 0.44uF, ESR – N/A, deviation: -6%

C503: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 1.31Ω, deviation: 0%

C504: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 1.18Ω, deviation: 0%

C505: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 2.1Ω, deviation: 0%

C506: rated capacitance – 3.3uF, measured – 3.2uF, ESR – 1.22Ω, deviation: -3%

C511: rated capacitance – 3.3uF, measured – 3.3uF, ESR – 3.7Ω, deviation: 0%

C512: rated capacitance – 3.3uF, measured – 3.4uF, ESR – 1.87Ω, deviation: +3%

C513: rated capacitance – 100uF, measured – 181uF, ESR – 0.21Ω, deviation: +81%

C514: rated capacitance – 100uF, measured – 168uF, ESR – 0.22Ω, deviation: +68%

C515: rated capacitance – 3.3uF, measured – 3.2uF, ESR – 1.18Ω, deviation: -3%

C516: rated capacitance – 3.3uF, measured – 3.4uF, ESR – 1.32Ω, deviation: +3%

C521: rated capacitance – 100uF, measured – 93uF, ESR – 0.13Ω, deviation: -7%

Vari-matrix unit - before and after

Buffer Amplifier Board (PD01)

The buffer amplifier has 8 low leakage e-caps (CD01, CD02, CD03, CD04, CD05, CD06, CD07, CD08) and one aluminum electrolytic capacitor CD09. The original low leakage e-caps were replaced with modern low leakage Nichicon UKL caps. The aluminum e-cap CD09 was replaced with a low impedance Nichicon UPW cap.

I noticed some inconsistencies between the schematic and what was installed on this board. According to the diagram and parts list in the service manual, the 4 low leakage capacitors CD01 to CD04 should be 1uF/50V. However, the capacitors installed in these positions are rated at 4.7uF/25V. This board has not been previously serviced and everything looks original and pristine. So, I replaced them with Nichicon UKL low leakage 4.7uF/50V capacitors. Service manuals from that era are notorious for a lot of errors. I believe this was a minor modification during the production of this model and was not well documented.

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

CD01: rated capacitance – 4.7uF, measured – 4.7uF, ESR – 1.78Ω, deviation: 0%

CD02: rated capacitance – 4.7uF, measured – 5.3uF, ESR – 1.56Ω, deviation: +13%

CD03: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 1.11Ω, deviation: +9%

CD04: rated capacitance – 4.7uF, measured – 5.2uF, ESR – 0.93Ω, deviation: +11%

CD05: rated capacitance – 10uF, measured – 11uF, ESR – 0.74Ω, deviation: +10%

CD06: rated capacitance – 10uF, measured – 10uF, ESR – 0.93Ω, deviation: 0%

CD07: rated capacitance – 10uF, measured – 10uF, ESR – 1.31Ω, deviation: 0%

CD08: rated capacitance – 10uF, measured – 10uF, ESR – 0.76Ω, deviation: 0%

CD09: rated capacitance – 100uF, measured – 113uF, ESR – 0.21Ω, deviation: +13%

Buffer amplifier board - before and after

Phono Amplifier Board (P400)

The phono amplifier board has 4 low leakage e-caps (C401, C402, C411, C412) installed in the signal path and 3 aluminum electrolytic capacitors (C409, C410, C413). The original low leakage e-caps with a rated capacitance of 1uF were replaced with film polyester WIMA caps. The other 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 phono amplifier board:

C401: rated capacitance – 4.7uF, measured – 4.7uF, ESR – 1.35Ω, deviation: 0%

C402: rated capacitance – 4.7uF, measured – 4.3uF, ESR – 1.55Ω, deviation: -9%

C409: rated capacitance – 220uF, measured – 242uF, ESR – 0.14Ω, deviation: +10%

C410: rated capacitance – 220uF, measured – 249uF, ESR – 0.15Ω, deviation: +13%

C411: rated capacitance – 1uF, measured – 1.3uF, ESR – 1.9Ω, deviation: +30%

C412: rated capacitance – 1uF, measured – 1.3uF, ESR – 2.2Ω, deviation: +30%

C413: rated capacitance – 100uF, measured – 116uF, ESR – 0.38Ω, deviation: +16%

Phono amplifier board - before and after

400 Hz Oscillator & Meter Driver Board (PL01)

This board has 8 aluminum electrolytic capacitors: CL05, CL06, CL07, CL10, CL11, CL12, CL13, CL14. They have all been replaced with low impedance Nichicon UPW caps. Note that the e-cap CL14 is soldered on the back (foil) side of the PCB. Also, pay attention to the polarity of this cap. The schematic shows the correct polarity (the negative lead of CL14 is soldered to the ground) but the PCB layout in the service manual shows the wrong polarity.

Test results on original capacitors removed from the 400 Hz oscillator & meter driver board:

CL05: rated capacitance – 10uF, measured – 16uF, ESR – 4.3Ω, deviation: +60%

CL06: rated capacitance – 10uF, measured – 15uF, ESR – 2.8Ω, deviation: +50%

CL07: rated capacitance – 10uF, measured – 15uF, ESR – 3.1Ω, deviation: +50%

CL10: rated capacitance – 10uF, measured – 13uF, ESR – 5.4Ω, deviation: +30%

CL11: rated capacitance – 10uF, measured – 14uF, ESR – 4.8Ω, deviation: +40%

CL12: rated capacitance – 10uF, measured – 12uF, ESR – 5.6Ω, deviation: +20%

CL13: rated capacitance – 10uF, measured – 12uF, ESR – 5.4Ω, deviation: +20%

CL14: rated capacitance – 33uF, measured – 42uF, ESR – 0.23Ω, deviation: +27%

400 Hz oscillator & meter driver board - before and after

Dolby Unit (P600)

The Dolby unit has 2 low leakage e-caps (C601, C602) and 17 aluminum electrolytic capacitors (C607, C608, C609, C610, C611, C612, C613, C614, C623, C624, C627, C628, C631, C632, C635, C636, C641). The original 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 Dolby unit:

C601: rated capacitance – 3.3uF, measured – 3.2uF, ESR – 2.9Ω, deviation: -3%

C602: rated capacitance – 3.3uF, measured – 3.0uF, ESR – 2.8Ω, deviation: -9%

C607: rated capacitance – 10uF, measured – 12uF, ESR – 5.1Ω, deviation: +20%

C608: rated capacitance – 10uF, measured – 12uF, ESR – 4.5Ω, deviation: +20%

C609: rated capacitance – 10uF, measured – 15uF, ESR – 3.2Ω, deviation: +50%

C610: rated capacitance – 10uF, measured – 15uF, ESR – 3.8Ω, deviation: +50%

C611: rated capacitance – 10uF, measured – 15uF, ESR – 5.1Ω, deviation: +50%

C612: rated capacitance – 10uF, measured – 13uF, ESR – 3.5Ω, deviation: +30%

C613: rated capacitance – 10uF, measured – 14uF, ESR – 5.0Ω, deviation: +40%

C614: rated capacitance – 10uF, measured – 15uF, ESR – 4.0Ω, deviation: +50%

C623: rated capacitance – 10uF, measured – 15uF, ESR – 4.2Ω, deviation: +50%

C624: rated capacitance – 10uF, measured – 13uF, ESR – 4.8Ω, deviation: +30%

C627: rated capacitance – 47uF, measured – 56uF, ESR – 0.57Ω, deviation: +19%

C628: rated capacitance – 47uF, measured – 54uF, ESR – 0.48Ω, deviation: +15%

C631: rated capacitance – 10uF, measured – 14uF, ESR – 4.6Ω, deviation: +40%

C632: rated capacitance – 10uF, measured – 13uF, ESR – 5.2Ω, deviation: +30%

C635: rated capacitance – 10uF, measured – 13uF, ESR – 5.0Ω, deviation: +30%

C636: rated capacitance – 10uF, measured – 15uF, ESR – 4.2Ω, deviation: +50%

C641: rated capacitance – 220uF, measured – 291uF, ESR – 0.09Ω, deviation: +32%

Dolby unit board - before and after

Dial and Meter Lamps

The old incandescent lamps were replaced with warm white LED lamps to maintain the original look and decrease heat. The original incandescent lamps behind two meters were also replaced with warm white LED lamps. The old yellowish vellum behind the dial scale was replaced with new heavyweight vellum paper.

Dial scale removed - original incandescent dial lamps

Dial scale removed - warm white LED lamps

Additional Troubleshooting

Upon completion of the restoration, I ran into an additional problem. I was not able to adjust the bias in the right channel of the rear power amplifier board. The DC voltage between pins J718 and J712 was ~0.4V regardless of the position of trimming resistor R738. The trimming resistor R738 is shunted by diode H719. I tested both the trimming resistor and the diode, and the diode H719 was short. I replaced the original diode M8513A installed in position H719 with a new OnSemi 1N4448 but was still not able to adjust the bias. Further diagnostics showed that one of the two current-limiting transistors was faulty (H707, open base-emitter junction). I replaced both current-limiting transistors H707 and H709 with new OnSemi KSC945 and KSA992, respectively. Also, the original resistor R758 was toasted and replaced in the past, but a new resistor with the wrong resistance rating was installed (330Ω instead of 39Ω). I replaced this resistor with a new KOA Speer metal film resistor. After all these replacements, I was able to adjust the bias to ~15mV in this channel (see the next "Audio Adjustments" section). Yes, restoring a quadraphonic receiver can be a difficult task.

Audio Adjustments 

To adjust a bias, connect the multimeter between pins J717 and J711, and adjust the trimming resistor R737 until the multimeter reads ~15mV DC. For the other channel, connect the multimeter between J718 and J712, and adjust the trimming resistor R738 for the same reading.

To adjust a clipping level, I connected my oscilloscope across the speaker terminals and applied a sine-wave signal of 1 kHz to the CD-4/AUX jacks. The trimming resistor R727 was adjusted for equal and symmetrical clipping. For the other channel, the trimming resistor R728 was adjusted.

Bias on the left and right channels after restoration (front board)

Bias on the left and right channels after restoration (rear board)

Output Power Test

The final output power test was performed at the end of my restoration. The Power Mode switch on the rear panel was switched to the 4-channel mode. 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 (front and rear speaker terminals) with no clipping up to: 9.62 VRMS (front speakers, left channel), 9.75 VRMS (front speakers, right channel), 9.93 VRMS (rear speakers, left channel), and 9.84 VRMS (rear speakers, right channel). It corresponds to the output power of 11.6W (front speakers, left channel), 11.9W (front speakers, right channel), 12.3W (rear speakers, left channel), and 12.1W (rear speakers, right channel).

Output power test (front speakers)

Output power test (rear speakers)

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. This unit looks great and sounds wonderful. Please watch a short demo video at the end of this post. Thank you for reading.

Marantz 4230 - after restoration

Demo video after repair & restoration