Yamaha CA-1000 Stereo Integrated Amplifier Restoration

Unit: Stereo Integrated Amplifier

Manufacturer: Yamaha

Model: CA-1000

SN: 23974

Today I'm showing a beautiful Yamaha CA-1000 stereo integrated amplifier that came in for restoration. This amplifier was manufactured from 1974 to 1976. It produces 70 watts (Class B) or 15 watts (Class A) per channel into 8 ohms. The total harmonic distortion is 0.1%. The damping factor at 8 ohms is 70. This amplifier is relatively small but heavy due to two large heat sinks, a massive transformer, and two large filter capacitors (18000uF/63V).

Servicing the Yamaha CA-1000 can be tricky for those without experience and/or the right tools, so think twice before attempting this project (many boards are inaccessible without disassembling the front panel chassis).

Power Supply Board (NA-06332)

The power supply board has 2 bi-polar capacitors (C711, C713) and 8 aluminum electrolytic capacitors (C705, C706, C707, C708, C709, C710, C714, C715).

The original bi-polar capacitor C711 with a nominal capacitance of 1uF was replaced with a WIMA film polyester cap. Another bi-polar cap C713 was replaced with a modern Nichicon UEP bi-polar cap. The e-cap C715 was replaced with a modern low-leakage Nichicon UKL cap. The remaining aluminum e-caps were replaced with Nichicon UPW/UPM low-impedance capacitors.

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:

C705: rated capacitance – 220uF, measured – 247uF, ESR – 0.34Ω, deviation: +12%

C706: rated capacitance – 220uF, measured – 238uF, ESR – 0.26Ω, deviation: +8%

C707: rated capacitance – 220uF, measured – 242uF, ESR – 0.36Ω, deviation: +10%

C708: rated capacitance – 220uF, measured – 240uF, ESR – 0.46Ω, deviation: +9%

C709: rated capacitance – 100uF, measured – 114uF, ESR – 0.66Ω, deviation: +14%

C710: rated capacitance – 100uF, measured – 132uF, ESR – 0.52Ω, deviation: +32%

C711: rated capacitance – 1uF, measured – 0.9uF, ESR – 4.2Ω, deviation: -10%

C713: rated capacitance – 100uF, measured – 107uF, ESR – 1.39Ω, deviation: +7%

C714: rated capacitance – 220uF, measured – 259uF, ESR – 0.46Ω, deviation: +18%

C715: rated capacitance – 47uF, measured – 45uF, ESR – 0.49Ω, deviation: -4%

The original Hitachi 2SC458 transistor installed in positions TR705, TR707, and TR709 is on my list of prone-to-failure transistors. I replaced all original 2SC458s with new Fairchild KSC1845 transistors. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

The three fusible resistors (FR701, FR702, FR705) were replaced with new Stackpole Electronics carbon film resistors. The other fusible resistor (FR703) was replaced with new Vishay fusible metal film resistors.

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

Power supply board - before and after

Microphone Amplifier Board (NA-06584)

The microphone amplifier board has 6 solid tantalum capacitors (C461, C462, C471, C472, C475, C476) installed in the signal path, and 6 aluminum electrolytic capacitors (C463, C464, C465, C466, C473, C474).

All original tantalum capacitors were replaced with modern low-leakage Nichicon UKL caps. The remaining aluminum e-caps were replaced with Nichicon UPW low-impedance capacitors.

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

C461: rated capacitance – 220uF, measured – 233uF, ESR – 0.51Ω, deviation: +6%

C462: rated capacitance – 220uF, measured – 228uF, ESR – 0.43Ω, deviation: +4%

C463: rated capacitance – 47uF, measured – 57uF, ESR – 0.88Ω, deviation: +21%

C464: rated capacitance – 47uF, measured – 54uF, ESR – 0.82Ω, deviation: +15%

C465: rated capacitance – 220uF, measured – 268uF, ESR – 0.91Ω, deviation: +22%

C466: rated capacitance – 220uF, measured – 262uF, ESR – 0.64Ω, deviation: +19%

C471: rated capacitance – 4.7uF, measured – 5.6uF, ESR – 0.72Ω, deviation: +19%

C472: rated capacitance – 4.7uF, measured – 5.4uF, ESR – 0.71Ω, deviation: +15%

C473: rated capacitance – 47uF, measured – 50uF, ESR – 1.43Ω, deviation: +6%

C474: rated capacitance – 47uF, measured – 52uF, ESR – 1.16Ω, deviation: +11%

C475: rated capacitance – 4.7uF, measured – 4.7uF, ESR – 1.68Ω, deviation: 0%

C476: rated capacitance – 4.7uF, measured – 5.0uF, ESR – 2.8Ω, deviation: +6%

Four NPN transistors (TR461, TR462, TR463, TR464) installed on this board are Hitachi 2SC1345. This transistor is on my list of transistors that are prone to failure. I replaced all original 2SC1345s with new Fairchild KSC1845 transistors. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

Microphone amplifier board - before and after

Function Board (NA-06583)

The serial number of the function board (NA-06583) installed in this amplifier differs from the serial number in the service manual (NA-06335).

I tried my best to identify each electronic component correctly, but some errors may still exist due to the lack of the correct circuit diagram.

The function board has 12 solid tantalum capacitors and 9 aluminum electrolytic caps.

All original tantalum capacitors with a nominal capacitance of 1uF or less were replaced with high-quality WIMA film polyester caps. The other 4 tantalum capacitors with a nominal capacitance of 4.7uF were replaced with low-leakage Nichicon UKL caps. The remaining aluminum e-caps were replaced with Nichicon UPW/UPM low-impedance capacitors.

Test results on original capacitors removed from the function board:

C417: rated capacitance – 1uF, measured – 1.1uF, ESR – 14.7Ω, deviation: +10%

C418: rated capacitance – 1uF, measured – 1.1uF, ESR – 14.5Ω, deviation: +10%

C423: rated capacitance – 10uF, measured – 12uF, ESR – 1.34Ω, deviation: +20%

C424: rated capacitance – 10uF, measured – 11uF, ESR – 1.84Ω, deviation: +10%

C427: rated capacitance – 0.47uF, measured – 0.45uF, ESR – N/A, deviation: -4%

C428: rated capacitance – 0.47uF, measured – 0.44uF, ESR – N/A, deviation: -6%

C429: rated capacitance – 100uF, measured – 123uF, ESR – 0.84Ω, deviation: +23%

C430: rated capacitance – 100uF, measured – 126uF, ESR – 0.79Ω, deviation: +26%

C443: rated capacitance – 220uF, measured – 225uF, ESR – 0.72Ω, deviation: +2%

C444: rated capacitance – 100uF, measured – 114uF, ESR – 0.92Ω, deviation: +14%

C445: rated capacitance – 4.7uF, measured – 5.5uF, ESR – 0.68Ω, deviation: +17%

C446: rated capacitance – 4.7uF, measured – 4.9uF, ESR – 1.05Ω, deviation: +4%

C449: rated capacitance – 4.7uF, measured – leaky/low capacitance

C450: rated capacitance – 4.7uF, measured – 4.9uF, ESR – 1.85Ω, deviation: +4%

C451: rated capacitance – 47uF, measured – 50uF, ESR – 1.35Ω, deviation: +6%

C4xx: rated capacitance – 33uF, measured – 34uF, ESR – 1.91Ω, deviation: +3%

C4xx: rated capacitance – 33uF, measured – 36uF, ESR – 1.77Ω, deviation: +9%

C4xx: rated capacitance – 0.68uF, measured – 0.66uF, ESR – N/A, deviation: -3%

C4xx: rated capacitance – 0.68uF, measured – 0.65uF, ESR – N/A, deviation: -4%

C4xx: rated capacitance – 1uF, measured – 1.0uF, ESR – 2.9Ω, deviation: 0%

C4xx: rated capacitance – 1uF, measured – 1.0uF, ESR – 3.8Ω, deviation: 0%

The six prone-to-failure Hitachi 2SC1345 transistors installed on this board were replaced with Fairchild KSC1845 transistors. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

The two fusible resistors FR401 and FR402 were replaced with new Vishay fusible metal film resistors.

Function board - before and after

Main Amplifier Board (NA-06588)

The serial number of the main amplifier board (NA-06588) installed in this amplifier differs from the serial number in the service manual (NA-06331).

I tried my best to identify each electronic component correctly, but some errors may still exist due to the lack of the correct circuit diagram.

Yamaha CA-1000 has two main amplifier boars. Each board is mounted directly on the heatsink with two power transistors. 

Each main amplifier board has 2 bi-polar capacitors (C601, C603) and one aluminum electrolytic capacitor C609.

The original bi-polar capacitor (C601, 2.2uF/25V) installed in the input signal path was replaced with a WIMA film polyester cap. Another bi-polar capacitor (C603, 47uF/50V) was replaced with a new bi-polar Nichicon UES cap. The remaining aluminum e-cap C609 was replaced with a Nichicon UPW low-impedance capacitor.

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

left channel:

C601: rated capacitance – 2.2uF, measured – 2.1uF, ESR – 3.9Ω, deviation: -5%

C603: rated capacitance – 47uF, measured – 49uF, ESR – 1.1Ω, deviation: +4%

C609: rated capacitance – 220uF, measured – 223uF, ESR – 0.66Ω, deviation: +1%

right channel:

C601: rated capacitance – 2.2uF, measured – 2.0uF, ESR – 4.6Ω, deviation: %

C603: rated capacitance – 47uF, measured – 48uF, ESR – 0.76Ω, deviation: %

C609: rated capacitance – 220uF, measured – 216uF, ESR – 0.82Ω, deviation: %

The first stage of the power amplifier circuit is a differential amplifier consisting of two amplifying transistors with a common emitter: TR602/TR603. The original PNP transistor installed in these positions is 2SA841. 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 ~5% (left channel) and ~14% (right channel). The mismatch on the right channel is relatively high. 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 2SA841s with a closely matched pair (within 1%) of modern Fairchild KSA992 low-noise transistors. The new transistor has the same pinout as the original one.

Test results on original 2SA841 transistors

TR602 (left channel): hfe - 291, Vbe - 0.770V 

TR603 (left channel): hfe - 306, Vbe - 0.765V

TR602 (right channel): hfe - 346, Vbe - 0.763V 

TR603 (right channel): hfe - 304, Vbe - 0.760V

Test results on new KSA992FBU transistors

TR602 (right channel): hfe - 414, Vbe - 0.763V

TR603 (right channel): hfe - 413, Vbe - 0.762V

TR602 (right channel): hfe - 415, Vbe - 0.762V 

TR603 (right channel): hfe - 418, Vbe - 0.762V

All the original power transistors were removed, degreased, and tested with an Atlas DCA55 semiconductor analyzer. They all passed the test and I installed them back with new Mica pads and fresh thermal paste.

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

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

Tone Amplifier Board (NA-06586)

The serial number of the tone amplifier board (NA-06586) installed in this amplifier differs from the serial number in the service manual (NA-06337).

I tried my best to identify each electronic component correctly, but some errors may still exist due to the lack of the correct circuit diagram.

The tone amplifier board has 6 solid tantalum capacitors (C301, C302, C317, C318, C319, C320) installed in the signal path, and 5 aluminum electrolytic capacitors (C311, C312, C313, C314, C339).

The original tantalum capacitors (C301 and C302) with a nominal capacitance of 1uF were replaced with WIMA film polyester caps. The other 4 tantalum capacitors were replaced with low-leakage Nichicon UKL caps. The remaining e-caps were replaced with Nichicon UPW low-impedance capacitors.

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

C301: rated capacitance – 1uF, measured – 1.1uF, ESR – 8.2Ω, deviation: +10%

C302: rated capacitance – 1uF, measured – 1.0uF, ESR – 6.2Ω, deviation: 0%

C311: rated capacitance – 10uF, measured – 12uF, ESR – 1.36Ω, deviation: +20%

C312: rated capacitance – 10uF, measured – 12uF, ESR – 1.54Ω, deviation: +20%

C313: rated capacitance – 100uF, measured – 116uF, ESR – 0.71Ω, deviation: +16%

C314: rated capacitance – 100uF, measured – 120uF, ESR – 0.64Ω, deviation: +20%

C317: rated capacitance – 3.3uF, measured – 3.5uF, ESR – 3.1Ω, deviation: +6%

C318: rated capacitance – 3.3uF, measured – 3.5uF, ESR – 4.2Ω, deviation: +6%

C319: rated capacitance – 33uF, measured – 36uF, ESR – 0.74Ω, deviation: +9%

C320: rated capacitance – 33uF, measured – 34uF, ESR – 0.75Ω, deviation: +3%

C339: rated capacitance – 220uF, measured – 255uF, ESR – 0.42Ω, deviation: +16%

The six prone-to-failure Hitachi 2SC1345 transistors installed on this board were replaced with Fairchild KSC1845 transistors. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

The original fusible resistor FR301 was replaced with a new Vishay fusible metal film resistor.

Tone amplifier board - before and after

Filter Board (NA-06581)

The serial number of the tone amplifier board (NA-06581) installed in this amplifier differs from the serial number in the service manual (NA-06338).

I tried my best to identify each electronic component correctly, but some errors may still exist due to the lack of the correct circuit diagram.

The filter board has 6 solid tantalum capacitors (C511, C512, C531, C532, C540, C541) installed in the signal path, and 7 aluminum electrolytic capacitors (C509, C510, C521, C522, C529, C530, C539).

The original tantalum capacitors (C511 and C512) with a nominal capacitance of 1uF were replaced with WIMA film polyester caps. The other 4 tantalum capacitors were replaced with low-leakage Nichicon UKL caps. The remaining e-caps were replaced with Nichicon UPW low-impedance capacitors.

Test results on original capacitors removed from the filter board:

C509: rated capacitance – 10uF, measured – 12uF, ESR – 1.28Ω, deviation: +20%

C510: rated capacitance – 10uF, measured – 12uF, ESR – 1.76Ω, deviation: +20%

C511: rated capacitance – 1uF, measured – 1uF, ESR – 4.2Ω, deviation: 0%

C512: rated capacitance – 1uF, measured – 1uF, ESR – 4.1Ω, deviation: 0%

C521: rated capacitance – 10uF, measured – 13uF, ESR – 1.22Ω, deviation: +30%

C522: rated capacitance – 10uF, measured – 12uF, ESR – 1.24Ω, deviation: +20%

C529: rated capacitance – 100uF, measured – 128uF, ESR – 0.72Ω, deviation: +28%

C530: rated capacitance – 100uF, measured – 127uF, ESR – 0.82Ω, deviation: +27%

C531: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 0.93Ω, deviation: +9%

C532: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 1.04Ω, deviation: +9%

C539: rated capacitance – 220uF, measured – 246uF, ESR – 0.54Ω, deviation: +12%

C540: rated capacitance – 2.2uF, measured – 2.3uF, ESR – 3.6Ω, deviation: +5%

C541: rated capacitance – 2.2uF, measured – 2.2uF, ESR – 4.8Ω, deviation: 0%

The four prone-to-failure Hitachi 2SC1345 transistors installed on this board were replaced with Fairchild KSC1845 transistors. Watch the pinout on replacement transistors. The original transistor is BCE and the new one is ECB.

The original fusible resistor FR501 was replaced with a new Vishay fusible metal film resistor.

Filter board - before and after

Operation Board (NA-06590)

The two original snap-action microswitches have been replaced with new Omron ones. These switches change the voltage on the secondary winding of the transformer between class A and class B. These two snap-action contacts can be damaged/welded together when switching from Class A to Normal mode with power on. So this is more of a preventative maintenance.

Snap-action Omron microswitches - original and new

Operational board - after servicing

Primary Stage, DC offset and Bias Adjustments

Four adjustments should be done to each main amplifier board: (i) primary stage differential amplification circuit current, (ii) mid-point voltage (or DC offset), (iii) idling current (or Bias, Class B), and (iv) idling current (or Bias, Class A). All steps are clearly described in the service manual.

(i) Connect the DC voltmeter between terminals TP1 (-) and TP2 (+). Adjust the voltage to 15V +/- 1V with the trimming resistor VR602.

(ii) Connect the DC voltmeter between terminals SP Out and E. Adjust the voltage to 0V +/- 10mV with the trimming resistor VR601.

(iii) Set the Operation switch to Normal. Connect the DC voltmeter between terminals TP3 (+) and TP4 (-). Adjust the voltage to 47mV +/- 10mV with the trimming resistor VR603.

(iv) Set the Operation switch to Class A. Connect the DC voltmeter between terminals TP3 (+) and TP4 (-). Adjust the voltage to 940mV +/- 50mV with the trimming resistor VR604.

Primary stage differential amplification circuit current on the left and right channels after restoration

Mid-point voltage (or DC offset) on the left and right channels after restoration

Idling current (or Bias, Class B) on the left and right channels after restoration

Idling current (or Bias, Class A) 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 26.41 VRMS (left channel) and 26.97 VRMS (right channel) for Class B mode. It corresponds to the output power of 87.2W on the left channel and 90.9W on the right channel. For Class A mode, the maximum output sine-wave signal before clipping was 11.80 VRMS (left channel) and 11.92 VRMS (right channel). It corresponds to the output power of 17.4W on the left channel and 17.8W on the right channel.

Output power test (Class B)

Output power test (Class A)

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 wood case was treated with Howard's Restor-A-Finish.

The final result can be seen in the photos below. This amplifier looks and sounds truly amazing. Please watch a short demo video at the end of this post. Thank you for reading.

Yamaha CA-1000 - after restoration

Demo video after repair & restoration