Accuphase C-200II: Introduction

Over the time I had only two preamplifiers. A SONY TA-E77ESD and an Accuphase C-200II. While I very much liked and enjoyed the SONY unit, I sold it in the end and redirected the income to the next acquisition which is also the subject of this article.

An Accuphase C-200 preamplifier is a quality machine that sound very transparent. The signal passes through it seamlessly. The construction is rugged and reliable. There are only two bipolar electrolytic capacitors in the signal path. Serviceability is very good due to the modular construction. However it has some drawbacks as well: soldering on these boards is a bit tricky and axial electrolytic capacitors are hard to find. Other than that, there is almost no issue with using or servicing one of these.

Mine has a problem related to the phono pick-up preamplifier. In about half an hour of usage it develops an annoying low frequency hum over the audio signal. There is something that heats up and generates this hum. When it's cold, the sound is great. Time to fix it. While here, I will also exchange the old electrolytic capacitors with new ones. It is known that these units run very hot inside. There are some resistors that are prone to failures. I will exchange them to new ones providing some wattage derating as well.

Let's see how hard can it be working on these old single layer ELNA boards with through hole copper electroplating -- argh!

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Accuphase C-200II: Technical Data

This preamplifier has the following technical characteristics.

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Accuphase C-200II: Parts List

I have assembled a parts list for this preamplifier. My restoration targets mainly the electrolytic capacitors but also some of the power resistors. Because I am aiming for maximum reliability and low maintenance, some of the electrolytic capacitors were replaced with film counterparts. Below you will find lists consisting of the various parts in this preamplifier.

The schematic value corresponds to what normally can be found in the electrical schematics. The recommended value is what I replaced the former part with. The BP inscription signifies a bipolar capacitor.

Descriptions and Parts Listings

Chassis

There are a few parts scattered around the steel chassis mounted to various connections points. I list them all here.

The Equalizer Amplifier Assemblies consist of two identical printed circuit boards (PCBs) that occupy positions 6 and 7 counting from the first board on the left. In older versions of this preamplifier I have seen differently branded PCBs. I am talking about Kensonic instead of the more recent Accuphase one. The name doesn't really matter that much. Mine has the newer revision boards branded Accuphase. The layout is a bit different and I am sure there are some improvements as well. The most noticeable one is that the regulator power transistors now are mounted on heatsinks.

The parts from the table below need to be ordered twice.

The Tone Control Assembly consists of one printed circuit board that occupies position 5 counting from the first board on the left.

The Filter/Output Assemblies consist of two identical printed circuit boards that occupy positions 3 and 4 counting from the first board on the left.

The parts from the table below need to be ordered twice.

The Headphone Amplifier Assembly consists of one printed circuit board that occupies position 2 counting from the first board on the left.

The Power Supply Assembly consists of one printed circuit board that occupies position 1 counting from the first board on the left.

The Fuse Circuit Assembly is located under the steel chassis in a topmost center location.

There is only a handful of electrolytic capacitors to be replaced. In my unit none of the small-signal transistors was defective. However as you already saw in the parts list, some of the resistors were replaced with higher power ones.

Do not hurry, take your time and do the job once. And do it well.

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Accuphase C-200II: Restoration

Servicing a C-200II unit is fairly simple because of the few parts involved in the restoration and the full modular construction. However your soldering tools and skills will need to pass the exam of their life. The factory flow solder looks very bad and brittle but ensures a good electrical contact. But the solder joints that have been exposed to massive heat -- think power resistors and power transistors -- are brittle and will crack quickly when you touch them with the iron tip. Using a quality solder sucker will clean perfectly the solder pads. Then you need to use flux paste and quality eutectic solder in order to re-tin the pads. I re-tinned every solder joint on every board of this preamplifier unit.

General Considerations

I should begin by saying that working on this preamplifier presents a very big health hazard. There are lethal voltages inside. Not knowing what you are doing might result in severe accidents and possibly death by electrocution. I am very skilled in electronics repair and I have been doing such repairs for almost 20 years. This qualifies me to work in this field. But if you do not have experience, please take this information just as a knowledge base. Do not attempt to repair something that you cannot handle as there is a big probability to severe it further while also suffering accidents.

Good working condition tools are also necessary for this restoration. I am using a quality temperature regulated soldering station with multiple tips for every situation that I could possibly encounter. Also I am using a good solder pump and quality desoldering wick in two sizes. Isopropyl alcohol is handy to decontaminate boards of old flux and other residues. I also use eutectic formulation quality solder. Every replacement part is brand new, from a reputable manufacturer, ordered from U.S.A., Japan, or Germany. Also I only use parts that are suitable as replacements in various sections of the preamplifier, after inspecting and comprehending the original schematic. Last but not least I have the years of experience backing up every action that I take while working on this unit.

I have found out that working with a temperature of exactly 300 degrees Celsius is sane for these Accuphase - ELNA vintage printed circuit boards. I have never lifted a pad with this temperature. But it is also true that I never wait more than three seconds with the soldering tip on a pad. While working on the chassis, I am pumping up between 360 and 440 degrees Celsius in the soldering iron.

Flux fumes are extremely toxic and should be avoided at all costs. Especially toxic are the fumes released while working on these old Japanese electronic boards.

Chassis Restoration

Underneath the steel chassis there are four electrolytic capacitors to change soldered directly on the equalizer board wire connection posts. Additionally there are two bipolar electrolytic capacitors in the back of the unit. On top of the steel chassis there are six clamped large can electrolytic capacitors used for power supply filtering purposes.

The four 1 uF / 80 V capacitors.

Their replacements.

All of them soldered in place. Leads are covered in thermo tube.

Detailed view.

The 68 uF / 16 V bipolar electrolytic capacitors.

And their replacements.

Equalizer Amplifier Assembly Restoration

These two boards contained the defect I was talking about in the first place in this article. Let me reiterate the problem: after some warm-up time -- half an hour or so -- an annoying hum will be present over the audio signal when using the DISC-1, DISC-2, or MIC inputs. That noise makes the preamplifier totally unusable.

Immediate candidates are the two electrolytic capacitors rated 47 uF / 25 V. These are located next to two very hot transistors. The ambient temperature will reach over 60 degrees Celsius in there.

Brittle solder joints.

I am using new capacitors from Nichicon BT series. These will work fine in an environment where the temperature can reach up to +125 °C while still delivering the factory specifications.

Glass beads are used as spacers in order to provide a minor airflow underneath the capacitors.

Quality solder and good skills will produce quality joints.

Looks nice overall.

The old capacitors are heat stressed. I have measured them and one is not registering and the other one appears as a 40 pF capacitor with massive internal leakage.

I have touched all solder joints and they look good now.

Even those belonging to the power transistors.

Next up is the other channel. The operations are identical so I will just put pictures.

I kind of like the blue color of the BT series capacitors.

Solder joints look nice and shiny.

Tone Control Assembly Restoration

On this board things look cooler -- no more heat discoloration of the PCB material. There are four electrolytic capacitors to change and two bipolar electrolytic capacitors that will be replaced with film counterparts.

Brittle solder joints again.

Vishay +125 °C electrolytic capacitors and Illinois Capacitor film parts.

Looks good.

A little bit oversized but they still fit the space.

On the tracks side I have corrected the brittle solder joints.

Filter/Output Assembly Restoration

Only two electrolytic capacitors to change on each of the two filter/output assemblies.

Solder looks better on the back-side. But still junk.

Restored.

Detailed view.

I have repaired all brittle solder joints.

The other channel follows soon.

Headphone Amplifier Assembly Restoration

This printed circuit board appears crowded. There are four electrolytic capacitors to change and four power resistors. Straightforward.

Brittle solder joints which crack very easily around the power resistors.

New Vishay electrolytic capacitors and new Panasonic power resistors. I chose to go with Panasonic parts because they look like the original ones. And they even have the same physical dimensions even though they have higher power specifications. In My case I have replaced the old 1 W resistors with new 2 W resistors. Derating will help with heat dissipation.

All new parts went in already. I have used new miniature glass tubes mounted on glass beads as spacers. These will aid to better heat dissipation.

I have re-worked all solder joints.

Power Supply Assembly Restoration

The least crowded of the plug-in printed circuit boards. This is home to six power resistors and six medium power transistors. In my unit there were no heatsinks mounted on top of the transistors. In other revisions of this preamplifier I have seen that all transistors on this board have heatsinks. So I ordered some TO-5 heatsinks.

Crappy solder joints.

Tubular glass beads, new Panasonic power resistors, and new aluminum TO-5 heatsinks.

As I don't have a tool for pressing heatsinks on the transistors, I have improvised as follows. A small vise was used to apply even pressure to the heatsink over the metal can transistor in a controlled manner. I have used two pine wood parts that I previously drilled so that transistor leads can safely enter the wood.

All transistors have their own heatsink now. Higher wattage resistors are in place.

Looking good already.

C7 is mounted on the solder side and is rated 33 uF / 25 V. I replaced it with a 33 uF / 100 V axial capacitor because that is what I had around.

Detail on the axial capacitor. I used tubular glass beads as insulators. I also made sure the capacitor is mounted 0.5 cm higher above the PCB so that eventual radiated heat diminishes until it reaches the capacitor. This should help prolonging its lifespan.

Fuse Circuit Assembly Restoration

Only three capacitors to change here. Two of them were rated 470 uF / 35 V and the other one was rated 220 uF / 25 V. I have replaced all of them with Vishay parts with an increase of operating voltage.

Before the restoration.

After the restoration.

I have used glass tubing to space the capacitors from the PCB assembly.

Overview

Here are the printed circuit boards all socketed in their corresponding place. The middle metallic cages and the rear metallic shield are removed for display purposes. Once I cleaned them of all the accumulated dust, I mounted them back.

Notice the bent fixture of the filtering capacitors on the left side. Either these were factory mounted as such or somebody before me messed with them. However they are due to change in the close future.

Aftermath

Old parts that have been removed from this preamplifier.

Heated capacitors.

This is all the work I did so far.

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Accuphase C-200II: Impressions

So how does it sound now? Same as before but without the annoying hum. Listening to vinyl discs is again a great audio experience.

I should add that working on this unit reminded me of the work I did on the Sansui AU-9500 amplifier. Construction quality is similar and socketed boards are a nice feature in terms of serviceability.

This restoration was a success. Until the next maintenance, this topic is closed.

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Accuphase C-200II: Further Impressions

An interesting thing is that the unit runs cooler after the restoration. I have recorded some cassette tapes and used the preamplifier extensively for an entire weekend. I was surprised to check an incredibly lower temperature than ever before. Compared to the previous times when after an hour or so the entire metal case was boiling, heck even the INPUT and TAPE MONITOR knobs were hot, now the case is at a nice 35-40 degrees Celsius.

Interesting. I reckon high ESR of the old capacitors was contributing to the regulator transistor heat build-up. It is just a wild supposition. I have not conducted scientific experiments to back-up what I am saying.

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Accuphase C-200II: Equalizer Amplifier Fault

Yesterday I wanted to listen to a Cesaria Evora vinyl disc and I fired up the audio installation. To my surprise, only the right channel worked. Total silence in the left speaker. I did all I could do to test the bad channel without opening up the unit but to no success. I listened to the disc as mono while thinking what could be the problem.

Today I opened the thing up and inverted the two individual equalizer printed circuit boards. Now the left channel was working. I pulled out the damaged board and started measuring the usual suspects: transistors, both small and medium signal. Thus I found out a shot Sony 2SC805A transistor in the top of the PCB assembly. Off to eBay and I ordered four transistors. Now I am waiting for them.

Ah the joy of using vintage HI-FI units...

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Accuphase C-200II: Fixing the Equalizer Amplifier

The genuine Sony 2SC805A transistors have arrived today.

Time to extract the shot transistor from the left channel equalizer amplifier PCB. The B-E junction is interrupted, reading infinity on the ohmmeter.

While extracting the transistor is a very simple operation, removing its heatsink is a difficult one without the right tools. I don't know how a right tool for this operation looks like but I have improvised. Thus I manufactured my own tool using a vise and some wooden blocks.

Putting the heatsink on the new transistor is equally easy with the vise and the wooden blocks.

New versus old.

The repaired printed circuit board is pictured below. A trained eye will spot the new Sony transistor is of group M23 while the old one is of group H23 -- whatever this means.

I loaded the PCB back in its slot inside the preamplifier and put a disc on the turntable. Both channels are loud and clear. I cannot spot any differences whatsoever either while listening to speakers or to headphones. Sometimes during a cold winter evening I might put this preamplifier to test with the signal generator, frequency counter, and the oscilloscope. But for the moment that's about it. I'm going to listen to a disc now.

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Please note that all the work presented herein this site is non-commercial. This is my hobby and I am doing this in my spare time. Through this page I freely share my knowledge with you. But if you like my work, please consider helping me buy a transistor or a capacitor for my projects.

Thank you!

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