Article #4 | 07:00 PM Monday 21/01/2019
Restoration
Servicing a C-200II unit is a fairly simple job. Mostly because there are only a few parts that need to be replaced. In addition, the fully modular construction makes disassembly a breeze. However, your soldering tools and skills will need to pass a hard exam. While the factory flow solder job looks very bad and brittle, it still ensures good electrical contact. But the solder joints that have been exposed to massive heat -- think power resistors and power transistors -- are brittle and will quickly crack when you touch them with the hot iron tip. Using a quality solder sucker will perfectly clean the solder pads. But then it's mandatory to use flux paste and quality eutectic solder in order to re-tin the pads. I have re-tinned every solder joint on every board of this preamplifier unit. It was a tedious job, but it paid off.
General Considerations
Working on this unit exposes you to electrical hazards. There are lethal voltages inside.
Severe accidents and possibly death by electrocution might occur. I am qualified and skilled at electronics and I have been doing audio gear repairs for over 20 years. If you lack experience, please take these articles as just a knowledge base. Do not attempt to repair something that you cannot handle as there is a high chance of doing further damage while also possibly suffering accidents.
Good tools are a must for a quality restoration. I use eutectic soldering alloy and a temperature-controlled soldering station equipped with various tip shapes. I have both standard and precision desoldering pumps and desoldering wicks of various widths. To clean the flux, I use isopropyl alcohol and high-purity acetone.
Empirically, I found that soldering at a temperature of exactly 300 °C is safe for these vintage printed circuit boards. I have never lifted any pads and I never wait more than a couple of seconds with the hot tip on any pad. While working on the chassis, I use between 360 and 440 °C. Flux fumes are extremely toxic and should be avoided at all costs.
Every replacement part is brand new, from a reputable manufacturer, ordered from the U.S.A., Japan, or Germany. In addition, I only use parts that are suitable for specific circuit sections, after inspecting and comprehending the original schematic diagrams. Last but not least, I have years of experience backing up my choices and actions.
Sometimes, I like to take unnecessary actions, such as replacing perfectly working components for futureproofing, or completely stripping down PCBs of parts for a better cleaning. While tedious, I have fun while doing so, and I also learn a thing or two in the process.
Chassis Restoration
Underneath the steel chassis there are four electrolytic capacitors to change soldered directly onto the equalizer board wire(wrap) 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 electrolytic capacitors.
And their film replacements.
All of them soldered in place. Their leads are covered in heat shrink tube.
Detailed view. Since I was out of transparent heat shrink tube, I resorted to using a black tube. The original construction involved transparent tubes. Oh, well...
The 68 uF / 16 V bipolar electrolytic capacitors.
Equalizer Amplifier Assembly Restoration
These two boards contained the defect I was talking about in the introductory section of this article. Let me reiterate the problem: after some warm-up time, say 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.
You'd think that the SONY-branded part, flanked by two styroflex capacitors in the lower right section, is an integrated circuit. But it's actually two MOS transistors within the same package, a solution chosen for temperature compensation and, since it's the same silicon, better matching of transistor characteristics.
Brittle solder joints.
I decided to use new capacitors from the Nichicon BT series as replacements. These are rated for a maximum temperature of +125 °C. They are a perfect fit for this circuit section, as the temperature between those medium-power SONY transistors rises quickly to an uncomfortable threshold.
Glass beads are used as spacers in order to provide some minor airflow underneath the capacitors.
Quality solder and good skills will produce quality joints. See the C6 and C7 pads, compared to the rest of the solder joints.
The PCB assembly looks nice overall, very original.
I was thinking about finding larger heat sinks for those transistors, but I had a hard time locating such hardware.
There is enough clearance for at least twice the height of the original heat sinks. We can see that even the transistor standoffs are tanned from the heat.
The old capacitors are visibly heat-stressed. Upon measuring them, one does not register, 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. The screws are now well embedded in solder alloy.
They surely used the best components available at the time. Silver mica capacitors are considered very high quality even these days.
Up next is the PCB for the other audio channel. Compared to the previous PCB, this one shows less of a heat discoloration around Q8. But there is no point in assuming it runs less hot.
But the same crappy solder joints are omnipresent.
The new Nichicon BT series capacitors and their "mounting hardware".
I kind of like the blue color of the BT series capacitors. It's very retro.
It's funny to see the complex heat sink for the power transistors on the lower left section of the PCB assembly. Most probably they realized the initial U-shaped heat sink was insufficient. Thus, a smaller U-shaped heat sink was bolted on top of the main heat sink, effectively increasing the heat dissipation area. But the complexity of this part easily increased the overall production cost. Marvelous.
The solder joints now look nice and shiny.
The solder mask has an unusual matte-reflective finish.
Tone Control Assembly Restoration
On this board things look cooler, andt here is 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.
These NTK-branded film capacitors are made by Nitsuko and are of very good quality.
Again, brittle solder joints.
Vishay +125 °C electrolytic capacitors and Illinois Capacitor film parts.
All done, the PCB looks good.
The replacement film capacitors are larger in diameter, but they still fit.
The axial electrolytic capacitors are bulkier than the original parts. I installed them slightly off the perpendicular axis, so that they fit. The initial components, while slimmer, were installed in a similar manner.
The 10 uF film capacitors are effectively resting on two resistors, there is one on each side of the capacitor.
On the solder side, I have corrected all brittle solder joints.
There is some discoloration on the tinned edge connector pads. While I don't think it's caused by heat, it might be some sort of corrosion, or interference caused by the different metal in the edge connector receptacle. However, I couldn't chemically remove it.
Filter/Output Assembly Restoration
There are only two electrolytic capacitors to replace on each of the two filter/output assemblies.
The solder job looks better on the back-side. But still junk.
The restored assembly.
Detailed view.
I have repaired all brittle solder joints.
The improvements and circuit correction on the solder side, looks very Sansui-esque. These kinds of revisions give a very human touch to electronics. While I initially hated seeing these mods, now I've grown to like them. Before I started restoring vintage audio gear, I figured that my brain was constantly poisoned by the cold perfection of the machine-assembled electronics of modern days.
The other channel follows next.
The situation is similar on the solder side.
These PCBs are branded Kensonic. From a history point of view, Accuphase was founded in 1972 by Jiro Kasuga, initially as Kensonic Laboratory, Inc. in Yokohama. He was a former Kenwood engineer.
The attention to details in those days was amazing for consumer-class audio gear.
And finally, I renewed the solder joints.
Headphone Amplifier Assembly Restoration
This printed circuit board appears crowded. But the design symmetry is clearly visible. There are four electrolytic capacitors to change and four power resistors. Straightforward.
Baked solder joints around the power resistors easily crack when exposed to the soldering iron tip. They even emit popping noises.
New Vishay electrolytic capacitors Panasonic power resistors. I went with Panasonic parts because they look like the original resistors. And they even have the same physical dimensions, albeit a higher power rating. I have replaced the old 1 W resistors with 2 W resistors. Derating will help a bit with heat dissipation.
While installing the new parts, I used some miniature glass tubes and glass beads as spacers. By raising the mounting height of the resistors, airflow is improved, and heat dissipation is better.
These black and red contraptions look interesting and highly unusual. I would've used only glass tubes if I had them in the optimal length. But I only had them in 5 mm length. Since I wanted at least 7 mm clearance, I went with this approach.
Accuphase originally used green glass beads. I didn't have green at the moment, but red did the trick.
Keen observation reveals the capacitive bypassing of the D1 and D2 diodes. By the way, these diodes are not individual, but there are actually three diodes per package. The schematic diagram specifies a 330 pF decoupling capacitor. But the PCB assembly diagram does not show C13 and C14 anywhere, although they are specified in the parts list. I suspect this is just another revision of an initial design.
I have re-worked all solder joints.
Power Supply Assembly Restoration
The least crowded of the plug-in printed circuit boards. This PCB holds six power resistors and six medium-power transistors that generate a fair amount of heat. In my unit there were no heat sinks mounted on top of the transistors. In other revisions of this preamplifier I have seen that all transistors on this board have heat sinks. So I ordered some TO-5 heat sinks.
Crappy solder joints.
Tubular glass beads, new Panasonic (Matsushita) power resistors, and new aluminum TO-5 heat sinks.
As I don't have a tool for pressing heat sinks on TO-5 case transistors, I have improvised as follows. A small vise was used to apply even pressure to the heat sink 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.
I used the smallest drill bit I had available, one that I had for at least 25 years, from a period when I etched my PCBs at home.
All transistors have their own heat sink now. Higher wattage resistors are in place.
The new heat sinks are a bit thinner than the original ones they used. But that's what I could find readily available. Anyway, a thinner heat sink is better than none.
Looking good already. I reused the tall glass beads of the original resistor marked as R11.
The new resistors look very retro. I initially wanted to use Dale resistors, but after a bit of research, I changed my mind.
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.
Details of the axial capacitor. I used tubular glass beads as insulators. I also made sure the capacitor is mounted 5 mm high above the PCB so that the eventual radiated heat is reduced by the time it reaches the capacitor. This should help prolong its lifespan.
Fuse Circuit Assembly Restoration
Only three capacitors to replace 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 operating voltage increase.
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 for a ​change in the near future.
It's clearly visible that there is enough space between the cards for taller TO-5 heat sinks. Maybe I will revisit this idea later on.
Aftermath
Old parts that have been removed from this preamplifier.
Heated capacitors.
This is all the work I did so far.
