Onkyo TX-2500 MKII Receiver Restoration

Unit: AM/FM Stereo Receiver

Manufacturer: Onkyo

Model: TX-2500 MKII

SN: 88107956 

Look what I have on my workbench today - a magnificent Onkyo TX-2500 MKII receiver! This model was manufactured from 1979 to 1980. It produces 40 watts per channel into 8 ohms with no more than 0.1% total harmonic distortion. The damping factor at 8 ohms is 40.

For some reason, Onkyo receivers tend to be less popular among vintage audio collectors and are often priced significantly lower than comparable Marantz, Sansui, or Pioneer models from the 1970s. Personally, however, I am a huge fan of the Onkyo MKII series. There is something almost magical about them: their distinctive aesthetic and characteristic sound possess a unique charm that truly draws me in. Currently, my personal collection includes two models from this lineup: the TX-1500 MKII and the TX-2500 MKII. Both are in excellent cosmetic condition. I hope that, one day, I will manage to acquire the remaining three models from this series as well.

Power Supply Board (NCPS-473)

The power supply board has 5 aluminum electrolytic capacitors C905, C910, C911, C914, and C917.

All original e-caps were replaced with low-impedance Nichicon UPW/UPM/UHE caps. 

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:

C905: rated capacitance – 220uF, measured – 261uF, ESR – 1.69Ω, deviation: +19%

C910: rated capacitance – 220uF, measured – 219uF, ESR – 3.6Ω, deviation: -1%

C911: rated capacitance – 220uF, measured – 221uF, ESR – 2.2Ω, deviation: +1%

C914: rated capacitance – 470uF, measured – 479uF, ESR – 1.61Ω, deviation: +2%

C917: rated capacitance – 220uF, measured – 295uF, ESR – 2.4Ω, deviation: +34%

The original Zener diode D912 was replaced with a new ON Semiconductor Zener diode to improve the reliability of the power supply circuit.

Power supply board - before and after

Tone Amplifier Board (NAAF-471)

This board is the most difficult to service due to the abundance of wires. I attempted to release it from the chassis, but doing so without removing the front chassis panel seems impossible. Nevertheless, it is still possible to service this board without removing it.

The tone amplifier board has 4 low-leakage capacitors (C353, C359, C453, C459) installed in the signal path, and 8 ordinary aluminum electrolytic capacitors (C365, C366, C369, C912, C465, C466, C470, C913).

The original low-leakage capacitors C353 and C453 were replaced with modern low-leakage Nichicon UKL capacitors. The other two original low-leakage capacitors, C359 and C459, as well as ordinary e-caps C366 and C466, were replaced with film polyester WIMA capacitors. The ordinary e-caps C365 and C465 were replaced with modern low-leakage Nichicon UKL capacitors to reduce noise in the circuit. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPM capacitors.

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

C353: rated capacitance – 2.2uF, measured – 2.3uF, ESR – 3.5Ω, deviation: +5%

C359: rated capacitance – 1uF, measured – 1uF, ESR – 3.4Ω, deviation: 0%

C365: rated capacitance – 22uF, measured – 24uF, ESR – 2.3Ω, deviation: +9%

C366: rated capacitance – 1uF, measured – 1.5uF, ESR – 3.1Ω, deviation: +50%

C369: rated capacitance – 220uF, measured – 265uF, ESR – 0.76Ω, deviation: +21%

C370: rated capacitance – 220uF, measured – 268uF, ESR – 1.02Ω, deviation: +22%

C453: rated capacitance – 2.2uF, measured – 2.3uF, ESR – 3.3Ω, deviation: +5%

C459: rated capacitance – 1uF, measured – 1uF, ESR – 3.2Ω, deviation: 0%

C465: rated capacitance – 22uF, measured – 24uF, ESR – 2.3Ω, deviation: +9%

C466: rated capacitance – 1uF, measured – 1.4uF, ESR – 3.2Ω, deviation: +40%

C912: rated capacitance – 470uF, measured – 533uF, ESR – 0.79Ω, deviation: +13%

C913: rated capacitance – 470uF, measured – 567uF, ESR – 0.86Ω, deviation: +21%

Tone amplifier board - before and after

Main Amplifier Board (NCDA-472)

The main amplifier board has 15 aluminum electrolytic capacitors C501, C504, C508, C511, C512, C513, C601, C604, C608, C612, C613, C703, C704, C915, C916.

The ordinary e-caps installed in the input signal path (C501 and C601) were replaced with modern low-leakage Nichicon UKL capacitors to reduce noise in the circuit. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW/UPM/UHE capacitors.

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

C501: rated capacitance – 2.2uF, measured – 2.3uF, ESR – 3.1Ω, deviation: +5%

C504: rated capacitance – 47uF, measured – 48uF, ESR – 2.6Ω, deviation: +2%

C508: rated capacitance – 47uF, measured – 54uF, ESR – 1.2Ω, deviation: +15%

C511: rated capacitance – 470uF, measured – 456uF, ESR – 1.3Ω, deviation: -3%

C512: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 3.3Ω, deviation: +9%

C513: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 3.2Ω, deviation: +9%

C601: rated capacitance – 2.2uF, measured – 2.0uF, ESR – 4.1Ω, deviation: -10%

C604: rated capacitance – 47uF, measured – 46uF, ESR – 2.3Ω, deviation: -2%

C608: rated capacitance – 47uF, measured – 55uF, ESR – 1.2Ω, deviation: +17%

C612: rated capacitance – 4.7uF, measured – 5.0uF, ESR – 3.1Ω, deviation: +6%

C613: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 3.4Ω, deviation: +9%

C703: rated capacitance – 220uF, measured – 265uF, ESR – 2.2Ω, deviation: +20%

C704: rated capacitance – 220uF, measured – 238uF, ESR – 0.9Ω, deviation: +8%

C915: rated capacitance – 47uF, measured – 33uF, ESR – 1.7Ω, deviation: -30%

C916: rated capacitance – 220uF, measured – 247uF, ESR – 2.1Ω, deviation: +12%

The original trimming resistors R515 and R615 were replaced with new Bourns potentiometers.

Main amplifier board - before and after

AM/FM Tuner and Equalizer Amplifier Board (NCRFE-470)

Equalizer Amplifier Circuit

The equalizer amplifier circuit has 2 low-leakage capacitors (C301 and C401) installed in the input signal path, and 6 aluminum electrolytic capacitors (C305, C309, C311, C312, C405, C409).

The original low-leakage capacitors were replaced with modern low-leakage Nichicon UKL capacitors. The ordinary aluminum e-caps (C309 and C409) installed in the output signal path were replaced with film polyester WIMA capacitors. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW capacitors.

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

C301: rated capacitance – 2.2uF, measured – 2.3uF, ESR – 3.7Ω, deviation: +5%

C305: rated capacitance – 47uF, measured – 45uF, ESR – 2.1Ω, deviation: -4%

C309: rated capacitance – 0.47uF, measured – 0.56uF, ESR – N/A, deviation: +19%

C311: rated capacitance – 3.3uF, measured – 3.6uF, ESR – 4.1Ω, deviation: +9%

C312: rated capacitance – 3.3uF, measured – 3.7uF, ESR – 3.4Ω, deviation: +12%

C401: rated capacitance – 2.2uF, measured – 2.4uF, ESR – 4.4Ω, deviation: +9%

C405: rated capacitance – 47uF, measured – 49uF, ESR – 2.4Ω, deviation: +4%

C409: rated capacitance – 0.47uF, measured – 0.59uF, ESR – N/A, deviation: +26%

AM/FM Tuner Circuit

The tuner circuit has 5 low-leakage capacitors (C118, C119 C122, C123, C124), and 15 aluminum electrolytic capacitors (C106, C108, C109, C113, C116, C127, C130, C131, C132, C134, C168, C169, C172, C173, C175).

The original low-leakage capacitors were replaced with film polyester WIMA and Kemet capacitors. Two ordinary aluminum e-caps (C109 and C172) were replaced with film polyester WIMA caps. The remaining aluminum e-caps were replaced with low-impedance Nichicon UPW/UPM capacitors.

Test results on original capacitors removed from the tuner circuit:

C106: rated capacitance – 4.7uF, measured – 5.1uF, ESR – 2.8Ω, deviation: +9%

C108: rated capacitance – 10uF, measured – 15uF, ESR – 2.8Ω, deviation: +50%

C109: rated capacitance – 0.47uF, measured – 0.62uF, ESR – N/A, deviation: +32%

C113: rated capacitance – 47uF, measured – 61uF, ESR – 1.3Ω, deviation: +30%

C116: rated capacitance – 470uF, measured – 656uF, ESR – 0.8Ω, deviation: +40%

C118: rated capacitance – 0.1uF, measured – 0.1uF, ESR – N/A, deviation: 0%

C119: rated capacitance – 0.1uF, measured – 0.1uF, ESR – N/A, deviation: 0%

C122: rated capacitance – 0.33uF, measured – 0.34uF, ESR – N/A, deviation: +3%

C123: rated capacitance – 0.47uF, measured – 0.44uF, ESR – N/A, deviation: -6%

C124: rated capacitance – 0.22uF, measured – 0.21uF, ESR – N/A, deviation: -5%

C127: rated capacitance – 3.3uF, measured – 3.6uF, ESR – 2.9Ω, deviation: +9%

C130: rated capacitance – 10uF, measured – 11uF, ESR – 2.7Ω, deviation: +10%

C131: rated capacitance – 10uF, measured – 12uF, ESR – 2.3Ω, deviation: +20%

C132: rated capacitance – 100uF, measured – 95uF, ESR – 1.1Ω, deviation: -5%

C134: rated capacitance – 100uF, measured – 106uF, ESR – 2.2Ω, deviation: +6%

C168: rated capacitance – 10uF, measured – 13uF, ESR – 2.4Ω, deviation: +30%

C169: rated capacitance – 220uF, measured – 332uF, ESR – 1.7Ω, deviation: +51%

C172: rated capacitance – 1uF, measured – 1.4uF, ESR – 2.9Ω, deviation: +40%

C173: rated capacitance – 3.3uF, measured – 3.8uF, ESR – 2.6Ω, deviation: +15%

C175: rated capacitance – 100uF, measured – 95uF, ESR – 0.8Ω, deviation: -5%

The failure-prone VD1212 dual diode installed in position D102 was replaced with a pair of 1N4148 diodes in series.

AM/FM Tuner and equalizer amplifier board - before and after

Filter Capacitors

The original filter capacitors (8,200uF/50V) were upgraded with new Kemet ALT22 series capacitors (10,000uF/63V). The new filter capacitor has the same diameter as the original.

New Kemet filter capacitors

Dial, Meter and Function Lamps

This receiver is equipped with two axial dial illumination lamps, positioned at the edges. I replaced them with warm white LED lamps.

Two meter and three indicator bulbs were replaced with new incandescent lamps. I recommend replacing the indicator bulbs from the front bracket side. The original rubber caps on the bulbs often degrade and become brittle over time. So, be careful not to damage them during the replacement process.

Dial lamps - original and warm white LED

Two meter lamps

Three indicator lamps

Bias Adjustment

The bias on each channel is measured between ID and CT terminals. The voltage should be adjusted to ~20mV with the trimming resistor R513 (left channel) and R613 (right channel).

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 19.14 VRMS (left channel) and 19.09 VRMS (right channel). It corresponds to the output power of 45.8W on the left channel and 45.6W on the right channel.

Output power test

I usually gently clean the faceplate in warm water with dish soap. But this is not the case for this receiver (as with any other Onkyo receiver from this series)! The lettering, silk screened onto the front aluminum faceplate can be easily flake off by improper cleaning. I had a very bad experience many years ago with an Onkyo TX-4500 MKII and I learned my lesson. The safest method is to gently, and I emphasize VERY gently, wipe the panel several times with a damp cloth. Be careful: do not ruin this magnificent receiver by using an unsuitable cleaning method.

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.

Onkyo TX-2500 MKII - after restoration

Demo video after repair & restoration

Onkyo TA-630D Cassette Deck Restoration

Unit: Stereo Cassette Tape Deck

Manufacturer: Onkyo

Model: TA-630D

SN: 10062943

I bought this cassette tape deck about two years ago from the original owner for just $25. The deck is in excellent cosmetic condition and there are only two almost invisible minor scratches on the faceplate. The owner told me that the last time he played the music on this deck was at least ten years ago. We met in a public place and I was not able to check whether it is working or not. But it was still a great deal since he wanted just $25 for it! I usually don't buy or restore vintage tape recorders because they often have problems with the transport mechanism, which I am not an expert in. But this tape deck was cheap, almost in perfect cosmetic condition, and most importantly for me, it has two large black VU meters! I am in love with vintage gears having VU meters. So, I bought it hoping to restore and keep it in my personal collection.

The Onkyo TA-630D is a stereo cassette deck with Dolby B noise reduction. It has 2 heads, belt-driven single-capstan transport, manual tape type selection handling normal, chrome and ferro-chrome tapes with additional manual equalization selection, and two large analog needle meters. The frequency response is from 30Hz to 18kHz on ferro-chrome tape and the signal to noise ratio is 68dB. It was manufactured from 1978 to 1980 with a list price of $350.

Belt Replacement

When I removed the top cover to check this unit inside I immediately noticed that we have a big problem here. The flat belt (Motor-Flywheel) and square-cut belt (Motor-pulley) have degraded so badly over time that both turned into sticky mush. Well, it looks like it wouldn't be an easy project. I checked online to get some guidance on how to replace these belts on this unit but with no success. There are just a few videos posted on YouTube about servicing Onkyo TA-630D but without good instructions for belt replacement. The service manual is also not very helpful for the belt replacement process. So, I decided to replace both belts based on my knowledge and experience with other cassette decks I restored before.

Further investigation revealed that this is definitely not a service-friendly cassette deck. I didn't find a way to replace two belts without disassembling and removing the metal bracket holding the motor and flywheel. Therefore, I initially removed the motor to clean its pulley from the sticky mush. This was an easy step but took some time to thoroughly clean the motor pulley from this messy stuff.

Sticky mush on the motor pulley from the old belt

Then, I tried to remove the sticky mush from the flywheel as much as possible before removing the metal bracket. I used a lot of Q-tips and isopropyl alcohol for that job.

Eventually, I unscrew four small screws, removed the metal bracket, and pulled out the flywheel. I recommend paying attention to this step and taking a lot of pictures. Don't lose the poly washer and tension spring from the flywheel!

Metal bracket holding the motor and flywheel

Metal bracket and flywheel removed

I removed the residue of the old belt from all pulleys and cleaned them with isopropyl alcohol. The old lithium grease on most metal levers was mostly dried out. I removed this grease from all parts as much as I could and applied a new white lithium grease. The FF key on this unit was stuck but eventually came free with a little extra effort. I exercised all keys to make sure that the new grease penetrated between each lever and everything works smoothly.

The new flat belt (Motor-Flywheel) was installed in two steps. First of all, I installed a flywheel back and put a new flat belt on it. Then I installed the metal bracket trying not to damage a new flat belt and secured it with four screws. This step is the most critical one because the working space is really very limited here and a new belt tends to come off from the flywheel. So, take your time and don't rush at this step. When the metal bracket was successfully installed I mounted the motor on it and secured it with two screws. Then, using a pair of tweezers I was able to hang the belt to the motor pin.

A new flat belt (Motor-Flywheel) installed

A new square cut belt (Motor-pulley) is fairly easy to install now since everything is mostly assembled. Double check the service manual to figure out how this belt should be installed. I used a pair of tweezers and with some patience was able to hang this belt as well.

A new square cut belt (Motor-pulley) installed

Cassette chassis assembled - back side

The last belt to replace is a counter belt. To access this belt one should remove the cassette door, cassette case, and cassette case plate. I didn't have any trouble removing these parts since the design is rather simple and it was intuitively clear what to do at each step.

Cassette door, case, and plate removed

Surprisingly but this belt survived and was still in pretty good condition. I vacuumed the deck chassis, cleaned the capstan, pinch roller, and both heads with isopropyl alcohol. Then applied a new white lithium grease to the rubbing metal parts and installed a new counter belt.

Clean chassis with new counter belt installed

For reference, I used the following belts in Onkyo TA-630D (Russell Industries, Inc. Cross-reference manual):

Flat belt (Motor-Flywheel) - FRZ7.5

Square cut belt (Motor-pulley) - SCQ8.2

Counter belt - SCY7.0

VU Meter Lamps

The lamp in the right channel VU meter has burned out and I decided to replace it with a new axial lamp. The meter is attached to the metal plate with double-sided tape. I used an X-ACTO #2 Knife to separate the meter from the metal plate. Pay attention to this step and don't apply too much force trying to separate it from the metal plate. Instead, try to carefully trim the double side tape with a proper knife/blade. The meter can be easily damaged due to extensive stress.

The lens is attached to the meter body with transparent tape which is not so easy to recognize at a first glance. I peeled off part of this transparent tape from the sides and carefully separated the lens from the meter body. According to the service manual, the original VU meter lamp is an axial 6.3V/100mA lamp. I replaced it with a new axial 6V/100mA lamp. The original lamp is a frosted bulb with a green tint whereas a new one is clear glass. I didn't find a suitable material to replicate the original green filter. The obvious option would be a green transparent tape wrapped around the lamp. But in that case, the tape would suffer from the extensive heat. So, I decided to leave it alone but also replace the original axial lamp from the left VU meter. At least both VU meters would match each other. Please leave a comment under this post if you have a better solution for a green filter.

VU Meters - the axial lamp in the right meter is burned out

Each VU meter is attached to the metal plate with a double-sided tape

Transparent tape on the sides of the VU meter lens

Right VU meter - burned axial lamp

Right VU meter - new axial lamp installed

VU meters with new axial lamps

I cleaned all the knobs and the faceplate in warm water with dish soap. All pots and switches 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 transport mechanism is working properly again, all levers move smoothly and I am enjoying how it looks and plays music. Thank you for reading.

Onkyo TA-630D - after restoration