Yamaha CR-440 Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Yamaha

Model: CR-440

SN: 213167

Today I'm showcasing a Yamaha CR-440 receiver that I bought a few months ago from the original owner. The unit was in faulty condition. According to the owner, one day it just stopped working. Well, I know what it means when the owner says "it just stopped working"... Anyway, the price was reasonable, the cosmetic condition was great and we made a deal.

The Yamaha CR-440 Natural Sound receiver was manufactured from 1979 to 1980. It produces 30 watts per channel into 8 ohms with a very low total harmonic distortion of 0.02%. The front panel of CR-440 is made of brushed aluminum and illuminated with a warm yellow-green light. It also has a matte finish look to all knobs and switches. With a wooden cabinet, the CR-440 looks very clean and bright.

Initial Evaluation and Troubleshooting

So, I used my Dim Bulb Tester (DBT) to initially power up this unit since the reason for the malfunction was unknown. The light bulb flashed for a second on bright and then dimmed out almost completely. The dial scale and both meters were lit but there was no sound from the headphones. I power cycled it again and noticed that the protection relay didn't engage. I checked the DC voltage across speaker terminals and it was close to zero volts as expected. Well, it's time to look inside.

The Yamaha CR-440 uses the IG02990 power amplifier packs instead of discrete power transistors. These packs were my major suspects. I measured the operating voltages on all pins of both IG02990 power amplifier packs and compared them to each other. The service manual has no information about a reference voltage on each pin but one can see that the measured voltage on pin 7 of IC301 (left channel) is ~32.2V. Such a high voltage is not expected on pin 7 since this pin is an output of IG02990. The typical voltage should be in the tens of millivolts. The measured voltage on pin 7 of IC302 (right channel) is ~21mV and it looks normal. The abnormal high voltage on pin 7 of IC301 is detected by the protection circuit. As a result, the relay is not engaging thereby protecting the speaker system.

Test results on IG022990 power amplifier packs (IC301 & IC302) - before restoration:

pin 1: left channel: 229mV, right channel: 126mV

pin 2: left channel: 0V, right channel: 0V

pin 3: left channel: 11.6V, right channel: 129mV

pin 4: left channel: -34.2V, right channel: -35V

pin 5: left channel: -32.2V, right channel: -1.19V

pin 6: left channel: -32.2V, right channel: -32.3V

pin 7: left channel: 32.2V, right channel: 21mV

pin 8: left channel: 32.2V, right channel: 32.4V

pin 9: left channel: 31.3V, right channel: 1.29V

pin 10: left channel: 30.4V, right channel: 30.3V

I unsoldered the left channel IG02990 power amplifier pack, removed it from the board, and powered up the unit. This time the relay clicked and I heard a clear sound from the right channel. Well, the power amplifier pack from the left channel is definitely toasted. I replaced this pack with another IG02990 which I bought a long time ago from the old stock. After installation, I powered up the unit and checked the operating voltages on all pins of both IG02990 packs again. The measured voltage on each pin was very similar between the two packs. The sound from both channels was clear without any distortion. The protection relay also worked as it should. Now it's time to move on with routine servicing.

Test results on IG02990 power amplifier packs (IC301 & IC302) - after restoration:

pin 1: left channel: 476mV, right channel: 129mV

pin 2: left channel: 0V, right channel: 0V

pin 3: left channel: 476mV, right channel: 132mV

pin 4: left channel: -35V, right channel: -35V

pin 5: left channel: -1.21V, right channel: -1.20V

pin 6: left channel: -32.6V, right channel: -32.6V

pin 7: left channel: 26mV, right channel: 22mV

pin 8: left channel: 32.6V, right channel: 32.6V

pin 9: left channel: 1.28V, right channel: 1.30V

pin 10: left channel: 30.2V, right channel: 30.2V

Original and new IG02990 power amplifier pack from the left channel:

Main Circuit Board

The main circuit board contains the voltage regulator/relay drive circuit, tone control circuit, and power amplifier circuit.

The voltage regulator/relay drive circuit has nine aluminum electrolytic capacitors C401 thru C404 and C409 thru C413. One of them (C402) is a bi-polar e-cap. I replaced it with a new bi-polar Nichicon UES cap. Note that the measured capacitance on the original e-cap C402 is only 41uF which is lower by almost 60% from the rated capacitance! The e-cap C412 (2200uF/25V) was not replaced since its ESR is zero and the measured capacitance is still very close to the rated one (only 2% deviation). The remaining seven aluminum e-caps were replaced with low impedance and high-reliability Nichicon UPW/UPM caps.

Test results on original capacitors removed from main circuit board (voltage regulator/relay drive circuit):

C401: rated capacitance – 33uF, measured – 36uF, ESR – 0.72Ω, deviation: +9%

C402: rated capacitance – 100uF, measured – 41uF, ESR – 0.64Ω, deviation: -59%

C403: rated capacitance – 470uF, measured – 454uF, ESR – 0.04Ω, deviation: -3%

C404: rated capacitance – 47uF, measured – 51uF, ESR – 0.18Ω, deviation: +9%

C409: rated capacitance – 22uF, measured – 26uF, ESR – 1.48Ω, deviation: +18%

C410: rated capacitance – 1000uF, measured – 1010uF, ESR – 0.02Ω, deviation: +1%

C411: rated capacitance – 100uF, measured – 105uF, ESR – 0.24Ω, deviation: +5%

C412: rated capacitance – 2200uF, measured – 2252uF, ESR – 0Ω, deviation: +2%

C413: rated capacitance – 4.7uF, measured – 5.3uF, ESR – 1.21Ω, deviation: +13%

The tone control circuit has ten aluminum e-caps: C301, C302, C305 thru C310, C321, and C322. Four of them (C301, C302, C321, C322) are installed in the signal path. I replaced them with high-quality film polyester capacitors to improve the signal-to-noise ratio: C301/C302 were replaced with Kemet caps, and C321/C322 were replaced with WIMA MKS2 caps. The remaining six aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from main circuit board (tone control circuit):

C301: rated capacitance – 0.22uF, measured – 0.24uF, ESR – N/A, deviation: +9%

C302: rated capacitance – 0.22uF, measured – 0.23uF, ESR – N/A, deviation: +5%

C305: rated capacitance – 220uF, measured – 266uF, ESR – 0.18Ω, deviation: +21%

C306: rated capacitance – 220uF, measured – 268uF, ESR – 0.19Ω, deviation: +22%

C307: rated capacitance – 10uF, measured – 12uF, ESR – 0.97Ω, deviation: +20%

C308: rated capacitance – 10uF, measured – 12uF, ESR – 1.04Ω, deviation: +20%

C309: rated capacitance – 10uF, measured – 12uF, ESR – 1.68Ω, deviation: +20%

C310: rated capacitance – 10uF, measured – 12uF, ESR – 1.81Ω, deviation: +20%

C321: rated capacitance – 1uF, measured – 1.2uF, ESR – 1.83Ω, deviation: +20%

C322: rated capacitance – 1uF, measured – 1.2uF, ESR – 1.58Ω, deviation: +20%

The power amplifier circuit has only two aluminum e-caps C325 and C326. I also replaced them with low impedance Nichicon UPW caps.

Test results on original capacitors removed from the main circuit board (power amplifier circuit):

C325: rated capacitance – 100uF, measured – 112uF, ESR – 0.33Ω, deviation: +12%

C326: rated capacitance – 100uF, measured – 108uF, ESR – 0.28Ω, deviation: +8%

Main circuit board - before and after

Tuner Circuit Board

The phono amplifier circuit is a part of the tuner circuit board. It has eight aluminum e-caps C108, C201, C202, C213 thru C216, and C218. Four of them C201/C202 and C215/C216 are installed in the signal path. I replaced two e-caps C201/C202 with low leakage Nichicon UKL caps and the other two C215/C216 with film polyester WIMA MKS2 caps. The remaining four aluminum e-caps were replaced with low impedance Nichicon UPW caps.

Test results on original capacitors removed from tuner circuit board (phono amplifier circuit):

C108: rated capacitance – 4.7uF, measured – 6.1uF, ESR – 0.79Ω, deviation: +30%

C201: rated capacitance – 10uF, measured – 12uF, ESR – 1.43Ω, deviation: +20%

C202: rated capacitance – 10uF, measured – 12uF, ESR – 1.62Ω, deviation: +20%

C213: rated capacitance – 220uF, measured – 262uF, ESR – 0.23Ω, deviation: +19%

C214: rated capacitance – 220uF, measured – 264uF, ESR – 0.21Ω, deviation: +20%

C215: rated capacitance – 0.47uF, measured – 0.53uF, ESR – N/A, deviation: +13%

C216: rated capacitance – 0.47uF, measured – 0.52uF, ESR – N/A, deviation: +11%

C218: rated capacitance – 10uF, measured – 11uF, ESR – 0.82Ω, deviation: +10%

Phono amplifier circuit - before and after

The voltage regulator circuit has four aluminum e-caps C154, C155, C151, and C161. I replaced the e-caps C154 and C155 with film polyester WIMA MKS2 caps. And other two e-caps C151 and C160 were replaced with low impedance Nichicon UPW caps. The e-cap C131 installed across signal meter leads was replaced with a Nichicon UPW cap.

Two aluminum e-caps C129 and C130 installed in the signal path of the tuner circuit were replaced with film polyester WIMA MKS2 caps. No other electrolytic capacitors were replaced on the tuner board.

Test results on original capacitors removed from tuner circuit board:

C129: rated capacitance – 1uF, measured – 1.1uF, ESR – 1.75Ω, deviation: +10%

C130: rated capacitance – 1uF, measured – 1.2uF, ESR – 1.83Ω, deviation: +20%

C131: rated capacitance – 220uF, measured – 261uF, ESR – 0.21Ω, deviation: +19%

C151: rated capacitance – 10uF, measured – 12uF, ESR – 1.71Ω, deviation: +20%

C154: rated capacitance – 1uF, measured – 1.2uF, ESR – 1.94Ω, deviation: +20%

C155: rated capacitance – 1uF, measured – 1.2uF, ESR – 1.74Ω, deviation: +20%

C160: rated capacitance – 10uF, measured – 13uF, ESR – 1.46Ω, deviation: +30%

Tuner circuit board - before and after

Output Power Test

At the end of my restoration, I loaded this receiver with a low inductance 8Ω/100W dummy resistor for each channel, connected my oscilloscope across the speaker terminals, and applied a sine-wave signal of 1kHz to the AUX jacks. The output sine-wave signal was perfectly symmetrical on both channels with no clipping up to 16.21 VRMS (left channel) and 16.35 VRMS (right channel). So, one can calculate that the output power is (16.21 x 16.21)/8=32.9W (left channel) and (16.35 x 16.35)/8=33.4W (right channel).

Output power test - meets and even exceeds a factory specification!

As usual, all the knobs and the faceplate were gently cleaned in warm water with dish soap. All the pots and switches were also thoroughly cleaned with DeoxIT 5% contact cleaner and lubricated with DeoxIT FaderLube 5% spray.

The final result can be seen in the photos below. All issues with electronics have been solved and the receiver works perfectly again. The sound is smooth and fairly well-detailed. Please watch a short demo video at the end of this post. Thanks for reading.

Yamaha CR-440 - after restoration

Demo video after repair & restoration