Yamaha CR-620 Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Yamaha

Model: CR-620

SN: 509018

A classic '70s receiver recently arrived on my bench for a complete restoration. The Yamaha CR-620 Natural Sound AM/FM receiver is a mid-range model from the renowned Yamaha CR-XX20 series, which includes the CR-220, CR-420, CR-620, CR-820, CR-1020, CR-2020, and CR-3020. This model was manufactured from 1977 to 1980. It produces 35 watts per channel into 8 ohms with no more than 0.05% total harmonic distortion. The damping factor at 8 ohms is 40. 

Main C. Board - 1, Amplifier (NA-06922-1)

The power supply & protection circuit has 18 aluminum electrolytic capacitors (C802, C803, CC804, C805, C806, C807, C808, C809, C810, C811, C812, C813, C814, C815, C816, C820, C825, C826). The two main filter capacitors (C823 and C824) are also installed on this board.

All original electrolytic capacitors (except the filter capacitors) were replaced with Nichicon UPW/UPM low-impedance capacitors. The original filter capacitors (C823 and C824) were replaced with Nichicon LKG caps. The LKG series was developed for high-quality audio equipment and is, in my opinion, the best replacement for original filter capacitors on the market.

The original e-caps were tested using an Atlas ESR70 capacitance meter, and the results are shown below. Note that many capacitors exhibit high ESR and/or capacitance values that fall outside factory specifications.

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

C802: rated capacitance – 1000uF, measured – 824uF, ESR – 0.72Ω, deviation: -18%

C803: rated capacitance – 100uF, measured – 110uF, ESR – 1.04Ω, deviation: +10%

C804: rated capacitance – 47uF, measured – 54uF, ESR – 2.3Ω, deviation: +15%

C805: rated capacitance – 470uF, measured – 538uF, ESR – 0.86Ω, deviation: +14%

C806: rated capacitance – 47uF, measured – 55uF, ESR – 1.12Ω, deviation: +17%

C807: rated capacitance – 47uF, measured – 57uF, ESR – 1.16Ω, deviation: +21%

C808: rated capacitance – 220uF, measured – 262uF, ESR – 1.06Ω, deviation: +19%

C809: rated capacitance – 100uF, measured – 98uF, ESR – 1.28Ω, deviation: -2%

C810: rated capacitance – 100uF, measured – 109uF, ESR – 0.96Ω, deviation: +9%

C811: rated capacitance – 100uF, measured – 96uF, ESR – 0.74Ω, deviation: -4%

C812: rated capacitance – 100uF, measured – 98uF, ESR – 0.68Ω, deviation: -2%

C813: rated capacitance – 22uF, measured – 23uF, ESR – 2.1Ω, deviation: +5%

C814: rated capacitance – 22uF, measured – 24uF, ESR – 2.1Ω, deviation: +9%

C815: rated capacitance – 4.7uF, measured – 4.4uF, ESR – 14.3Ω, deviation: -6%

C816: rated capacitance – 33uF, measured – 8uF, ESR – 6.4Ω, deviation: -76%

C820: rated capacitance – 47uF, measured – 62uF, ESR – 3.4Ω, deviation: +32%

C825: rated capacitance – 10uF, measured – 12uF, ESR – 8.6Ω, deviation: +20%

C826: rated capacitance – 10uF, measured – 11uF, ESR – 14.3Ω, deviation: +10%

Test results on the original filter capacitors:

C823: rated capacitance – 6800uF, measured – 3365uF, ESR – 1.89Ω, deviation: -51%

C824: rated capacitance – 6800uF, measured – 3374uF, ESR – 1.56Ω, deviation: -50%

All original transistors installed in the power supply & protection circuit were replaced to improve the reliability of the power supply. Below is a list of original and replacement parts that I have used.

TR802: NPN, 2SD234 (original), replaced with a new Fairchild MJE15032G

TR803: NPN, 2SD400 (original), replaced with a new Fairchild KSC2690AYSTU

TR804: NPN, 2SD400 (original), replaced with a new Fairchild KSC2690AYSTU

TR805: NPN, 2SC1918 (original), replaced with a new Fairchild KSC1845FTA

TR806: NPN, 2SC1918 (original), replaced with a new Fairchild KSC1845FTA

TR807: PNP, 2SA844 (original), replaced with a new Fairchild KSA992FBTA

TR808: NPN, 2SC1918 (original), replaced with a new Fairchild KSC1845FTA

TR809: PNP, 2SB544 (original), replaced with a new Fairchild KSA1013YBU

The main amplifier circuit has two low-leakage capacitors (C701, C702) installed in the input signal path, two bi-polar capacitors (C743, C744), and 8 aluminum electrolytic capacitors (C705, C706, C715, C716, C721, C722, C735, C736).

The original low-leakage capacitors were replaced with modern low-leakage Nichicon UKL caps. Two bi-polar capacitors and 4 ordinary e-caps (C721, C722, C735, C736) with a nominal capacitance of 1uF were replaced with high-quality WIMA film polyester caps. The remaining aluminum e-caps were replaced with Nichicon UPW low-impedance capacitors.

Test results on the original capacitors removed from the main amplifier circuit:

C701: rated capacitance – 47uF, measured – 24uF, ESR – 1.92Ω, deviation: -49%

C702: rated capacitance – 47uF, measured – 26uF, ESR – 1.85Ω, deviation: -45%

C705: rated capacitance – 220uF, measured – 167uF, ESR – 1.49Ω, deviation: -24%

C706: rated capacitance – 220uF, measured – 175uF, ESR – 1.22Ω, deviation: -20%

C715: rated capacitance – 47uF, measured – 58uF, ESR – 3.1Ω, deviation: +23%

C716: rated capacitance – 47uF, measured – 61uF, ESR – 3.2Ω, deviation: +30%

C721: rated capacitance – 1uF, measured – 1.4uF, ESR – 6.3Ω, deviation: +40%

C722: rated capacitance – 1uF, measured – 1.5uF, ESR – 4.6Ω, deviation: +50%

C743: rated capacitance – 1uF, measured – 1.3uF, ESR – 5.1Ω, deviation: +30%

C744: rated capacitance – 1uF, measured – 1.2uF, ESR – 6.5Ω, deviation: +20%

C735: rated capacitance – 1uF, measured – 1.3uF, ESR – 8.6Ω, deviation: +30%

C736: rated capacitance – 1uF, measured – 1.3uF, ESR – 6.7Ω, deviation: +30%

The first stage of the power amplifier circuit is a differential amplifier composed of two amplifying transistors with a shared emitter: TR701/TR703 and TR702/TR704. The original transistors installed in these positions are PNP 2SA872s, which are not on my list of infamous transistors prone to failure. However, it is always prudent to test the transistors in the differential amplifier to confirm they remain well-matched.

Testing revealed that the mismatch between the original transistors in the left channel is relatively small (~6%). In contrast, the mismatch in the right channel is significantly higher (~19%). To enhance the reliability of the differential amplifier, I opted to replace the original 2SA872 transistors in each pair with closely matched (within 1%) modern Fairchild KSA992 low-noise transistors. The new transistors have the same pinout as the original ones.

Test results on original 2SA872 transistors

TR701 (left channel): hfe - 364, Vbe - 0.770V 

TR703 (left channel): hfe - 342, Vbe - 0.768V

TR702 (right channel): hfe - 361, Vbe - 0.780V 

TR704 (right channel): hfe - 304, Vbe - 0.777V

Test results on new KSA992 transistors

TR701 (left channel): hfe - 480, Vbe - 0.758V 

TR703 (left channel): hfe - 480, Vbe - 0.760V

TR702 (right channel): hfe - 486, Vbe - 0.758V 

TR704 (right channel): hfe - 487, Vbe - 0.759V

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

Main C. Board - 1, Amplifier - before and after

Main C. Board - 2, Tone Control (NA-06922-2)

The tone control board has 6 low-leakage capacitors (C601, C602, C611, C612, C613, C614) installed in the signal path, two low-impedance capacitors (C619, C620), and 3 ordinary aluminum electrolytic capacitors (C609, C610, C631).

All the original low-leakage capacitors, along with the two low-impedance capacitors, were replaced with modern Nichicon UKL low-leakage capacitors. The remaining aluminum electrolytic capacitors were upgraded to Nichicon UPW low-impedance capacitors.

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

C601: rated capacitance – 10uF, measured – 9uF, ESR – 3.4Ω, deviation: -10%

C602: rated capacitance – 10uF, measured – 9uF, ESR – 2.2Ω, deviation: -10%

C609: rated capacitance – 47uF, measured – 59uF, ESR – 4.5Ω, deviation: +26%

C610: rated capacitance – 47uF, measured – 61uF, ESR – 3.2Ω, deviation: +30%

C611: rated capacitance – 47uF, measured – 24uF, ESR – 3.4Ω, deviation: -49%

C612: rated capacitance – 47uF, measured – 23uF, ESR – 4.2Ω, deviation: -51%

C613: rated capacitance – 100uF, measured – 33uF, ESR – 5.9Ω, deviation: -67%

C614: rated capacitance – 100uF, measured – 23uF, ESR – 6.2Ω, deviation: -77%

C619: rated capacitance – 100uF, measured – 28uF, ESR – 4.2Ω, deviation: -72%

C620: rated capacitance – 100uF, measured – 26uF, ESR – 2.8Ω, deviation: -74%

C631: rated capacitance – 10uF, measured – 11uF, ESR – 5.4Ω, deviation: +10%

Main C. Board - 2, Tone Control - before and after

Tuner C. Board - 1 (NA-06923-1)

Be aware, that replacing the original capacitors in the tuner section may require subsequent tuner alignment. I do not recommend servicing the tuner section of any vintage receiver unless you have all the necessary equipment and sufficient experience in tuner alignment.

The tuner circuit has 22 aluminum electrolytic capacitors: C112, C113, C114, C115, C202, C203, C204, C207, C208, C210, C211, C212, C223, C224, C302, C303, C306, C312, C313, C401, C402, C406.

All capacitors with a nominal capacitance of 0.22uF were replaced with Kemet film polyester caps, and the capacitors with nominal capacitances of 0.47uF and 1uF were replaced with WIMA film polyester caps. The remaining aluminum electrolytic capacitors were upgraded to Nichicon UPW low-impedance capacitors.

Test results on the original capacitors removed from the tuner circuit:

C112 rated capacitance – 1uF, measured – 1.4uF, ESR – 14.9Ω, deviation: +40%

C113: rated capacitance – 10uF, measured – 12uF, ESR – 8.2Ω, deviation: +20%

C114: rated capacitance – 47uF, measured – 61uF, ESR – 2.1Ω, deviation: +30%

C115: rated capacitance – 0.47uF, measured – 0.54uF, ESR – N/A, deviation: +15%

C202: rated capacitance – 100uF, measured – 128uF, ESR – 1.28Ω, deviation: +28%

C203: rated capacitance – 0.47uF, measured – 0.61uF, ESR – N/A, deviation: +30%

C204: rated capacitance – 10uF, measured – 10uF, ESR – 7.3Ω, deviation: 0%

C207: rated capacitance – 10uF, measured – 11uF, ESR – 11.6Ω, deviation: +10%

C208: rated capacitance – 0.22uF, measured – 0.21uF, ESR – N/A, deviation: -5%

C210: rated capacitance – 1uF, measured – 1.4uF, ESR – 8.4Ω, deviation: +40%

C211: rated capacitance – 220uF, measured – 256uF, ESR – 5.4Ω, deviation: +16%

C212: rated capacitance – 220uF, measured – 251uF, ESR – 4.5Ω, deviation: +14%

C223: rated capacitance – 0.47uF, measured – 0.61uF, ESR – N/A, deviation: +30%

C224: rated capacitance – 0.47uF, measured – 0.79uF, ESR – N/A, deviation: +68%

C302: rated capacitance – 1uF, measured – 1.6uF, ESR – 6.4Ω, deviation: +60%

C303: rated capacitance – 10uF, measured – 10uF, ESR – 15.3Ω, deviation: 0%

C306: rated capacitance – 1uF, measured – 1.5uF, ESR – 6.7Ω, deviation: +50%

C312: rated capacitance – 0.22uF, measured – 0.23uF, ESR – N/A, deviation: +5%

C313: rated capacitance – 3.3uF, measured – 3.4uF, ESR – 9.5Ω, deviation: +3%

C401: rated capacitance – 100uF, measured – 126uF, ESR – 2.8Ω, deviation: +26%

C402: rated capacitance – 10uF, measured – 9uF, ESR – 8.8Ω, deviation: -10%

C406: rated capacitance – 33uF, measured – 44uF, ESR – 1.87Ω, deviation: +33%

The phono amplifier is also located on this board. It has 4 low-leakage capacitors (C501, C502, C517, C518) installed in the signal path and 3 aluminum electrolytic capacitors (C515, C516, C520).

The original low-leakage capacitors were replaced with modern Nichicon UKL low-leakage capacitors, and the remaining aluminum electrolytic capacitors were upgraded to Nichicon UPW low-impedance capacitors.

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

C501 rated capacitance – 10uF, measured – 11uF, ESR – 3.8Ω, deviation: +10%

C502 rated capacitance – 10uF, measured – 10uF, ESR – 3.1Ω, deviation: 0%

C515 rated capacitance – 470uF, measured – 564uF, ESR – 1.33Ω, deviation: +20%

C516 rated capacitance – 470uF, measured – 546uF, ESR – 1.12Ω, deviation: +16%

C517 rated capacitance – 2.2uF, measured – 2.1uF, ESR – 4.2Ω, deviation: -5%

C518 rated capacitance – 2.2uF, measured – 2.1uF, ESR – 4.6Ω, deviation: -5%

C520 rated capacitance – 47uF, measured – 61uF, ESR – 1.31Ω, deviation: +30%

This board also houses four low-leakage capacitors (C671, C672, C677, C678) from the tone control circuit. All of them were replaced with modern Nichicon UKL low-leakage capacitors.

Test results on the original capacitors removed from the rest of the tone control circuit:

C671 rated capacitance – 10uF, measured – 10uF, ESR – 2.3Ω, deviation: 0%

C672 rated capacitance – 10uF, measured – 11uF, ESR – 1.9Ω, deviation: +10%

C677 rated capacitance – 2.2uF, measured – 2.1uF, ESR – 3.8Ω, deviation: -5%

C678 rated capacitance – 2.2uF, measured – 2.2uF, ESR – 3.7Ω, deviation: 0%

Tuner C. Board - 1 (NA-06923-1) - before and after

Power Transistors

The original PNP power transistor in the left channel was open, while the NPN power transistor in the right channel exhibited a relatively low current gain of 29. To address these issues, I replaced all the original transistors with new Onsemi MJ21193G (PNP) and MJ21194G (NPN) transistors. These modern transistors are optimized for high-power audio applications and offer excellent gain linearity. A fresh thermal compound and new Mica pads were applied between each power transistor and the heat sink.

left channel:

TR723 (2SD371, NPN), hfe - 84, Vbe - 0.626V

TR725 (2SB531, PNP), open collector-base

right channel:

TR724 (2SD371, NPN), hfe - 29, Vbe - 0.629V

TR726 (2SB531, PNP), hfe - 110 Vbe - 0.635V

Original and new power transistors

Dial and Meter Lamps

Two meters in the CR-620 are illuminated with three incandescent lamps. One of them was burned out. I replaced all of them with new incandescent lamps.

There is no backlit to the dial scale in CR-620 but the dial pointer is illuminated. This design makes it relatively easy to replace the burned pointer bulb. One just needs to unscrew two small screws on the top of the dial pointer unit and the lamp will be released.

Meter lamps - old and new

Dial pointer lamp - original and new

Bias Adjustment

The bias for the left channel is measured between TP1 (-) and TP2 (+), while the bias for the right channel is measured between TP3 (-) and TP4 (+). It should be adjusted to 8mV using the trimming resistors VR701 and VR702.

Bias on the left and right channels after restoration

Output Power Test

The final output power test was performed at the end of my restoration. The amplifier was loaded with a low inductance 8Ω/100W dummy resistor for each channel. The oscilloscope was connected across the speaker terminals and a sine-wave signal of 1kHz was applied to the AUX jacks. The output sine-wave signal was perfectly symmetrical on both channels with no clipping up to 18.51 VRMS (left channel) and 18.75 VRMS (right channel). It corresponds to the output power of 42.8W on the left channel and 43.9W on the right channel.

Output power test

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

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

Yamaha CR-620 - after restoration

Demo video after repair & restoration