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.
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 with 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 a standard and a precision desoldering pumps and desoldering wick in various widths. To clean the flux, I use isopropyl alcohol and high purity acetone.
Empirically, I found that working with 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 in 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.
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.
All of them soldered in place. Leads are covered in thermo tube.
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.
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.
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.
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.
Old parts that have been removed from this preamplifier.
This is all the work I did so far.