AKAI AA-5210 #1: Restoration
When these amplifiers go defective, they smell like cat urine. It is no joke. Electrolyte in these vintage capacitors smells bad. Mine was also suffering from 2SC458 and 2SC1313 transistor plague. And this amplifier is full of them. To sum up there are 4 x 2SC1313 on the equalizer board, 2 x 2SA725 and 4 x 2SC458 on the tone controls board, 2 x 2SC458 on the power amplifier board. I have replaced 2SC1313 and 2SC458 with Fairchild KSC1845 and 2SA725 with Fairchild KSA992. Note that the modern transistors need to be mounted in reverse as they have mirrored terminal disposition in respect to the old parts.
This unit had a very annoying popping and cracking sound when idling or playing music. The sound was dropping on one of the channels and high-end of the spectrum was badly reproduced in audio programs. Nothing that I cannot fix. So let's get to work.
New parts.
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 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.
96-5008 Power Amplifier Board Restoration
The power amplifier board is very crowded. A lot of resistors mounted vertically. But servicing is straightforward as you can expect. One big problem is the glue that was used at the factory to secure the output capacitors to the PCB. I handled this with D509 thinner. Careful with this as it is highly flammable and also volatile. The fumes are toxic. So you need a very good ventilation in order to work with it. However the glue is dissolved enough in a couple of minutes that you can peel it off with minimal effort.
The board before restoration.
C1, C1b, C5, and C5b are rated 2.2 uF / 50 V and were replaced with the same rating Nichicon FG series modern capacitors. C2 and C2b provide some local filtering and are rated 100 uF / 50 V. I replaced them with Nichicon KZ MUSE series parts of the same rating. C7 and C7b provide emitter decoupling for transistors TR2 and TR2b. They are 100 uF / 6.3 V and were replaced with Nichicon FG series capacitors rated 100 uF / 16 V. C9 and C9b are the speaker coupling capacitors. These are very important as they block DC from the power amplifier to reach the audio speakers. So quality parts are required for this purpose. Pay very good attention to what you put here. I have chosen Nichicon KZ MUSE series parts of the same rating. They are able to handle the current that passes to the speakers. C11 and C11b are used for local filtering purposes and are rated 220 uF / 35 V. I have replaced these with the same rating Nichicon FG series parts.
And after the restoration.
The solder has been re-newed on all terminals on the printed tracks side.
A5-5029 Tone Control Board Restoration
This board has a lot of capacitors and transistors to replace. But the good news is that it is fairly easy to service. However access to it is impossible as there is absolutely no clearance for the hands or the soldering iron. My way of doing this is to remove the knobs, then the front plate. After that I have removed the switches printed circuit board by unfastening the four securing screws on the front side of the chassis. Then I get the board out in a perpendicular orientation relative to the tone control board. This gives me enough clearance to work on A5-5029.
This is the board before the service operation.
Capacitors C1, C1b, C13, and C13b are rated 47 uF / 50 V. They were replaced with the same rating Nichicon KZ MUSE series modern parts. C5 and C5b were originally rated 47 uF / 6.3 V and were replaced with Nichicon KZ MUSE parts rated 47 uF / 25 V. C6 and C6b were 4.7 uF / 25 V and were replaced with Nichicon FG series capacitors rated 4.7 uF / 50 V. C10 and C10b were originally 10 uF / 25 V. I have used Nichicon KZ MUSE parts rated 10 uF / 50 V. C12 and C12b, originally rated 100 uF / 6.3 V were replaced with Nichicon KZ MUSE parts rated 100 uF / 25 V. C14 and C14b, rated 2.2 uF / 25 V were replaced with Nichicon FG series capacitors rated 2.2 uF / 50 V.
And here it is after servicing.
You can see here the vintage Japanese styroflex (polystyrene) capacitor manufactured by Nissei that I used to replace the existing 100 pF squared VFM capacitor. There was absolutely no electrical problem with the VFM Hi-Q capacitor. However it was fairly bulky and there was no way I could fit the new capacitors with it in place. So I changed it for a tubular-radial design.
I have renewed the solder joints of the component terminals.
A5-5028 Equalizer Board Restoration
To access the solder side of this board you only need to remove the bottom steel plate. Which I did already. Exchanging the parts is straightforward. 2SC1313 transistors were replaced with KSC1845 modern parts.
Here is the board before the job.
C1 and C2 were originally rated 100 uF / 16 V. I have replaced these with Nichicon KZ MUSE series parts rated 100 uF / 25 V. C3, C4, C9, and C10 were 1 uF / 50 V electrolytic capacitors. I used Panasonic stacked film modern counterparts of the same rating. C5 and C6 were 2.2 uF / 50 V and were replaced with the same rating Nichicon FG series capacitors. As for C7 and C8, they were rated 10 uF / 25 V. I have used Nichicon KZ MUSE parts rated 10 uF / 100 V because I had a great stock of these at that time. They fit perfectly and the layout raster is similar.
And here is the board after working on it. Note the transistors mounted in reverse. This is due to the modern parts having mirrored terminal disposition.
A trained eye will spot that I had to replace the very high quality 470 pF VFM capacitors with new-old-stock Nissei styroflex parts. The main reason is that these were too big, disallowing me to mount the 1 uF / 50 V stacked film replacements. I am keeping the VFM parts for other projects.
Check this weird solder joint. I spotted this while working on the solder side. Apparently the solder mask compound escaped the pads mold and ended up allowing for a bad electrical connection between this resistor and the printed circuit track. I have cleaned the pad thoroughly and then scratched the solder mask with an utility knife. Then I made a correct solder joint for a perfect electrical contact.
I have renewed the solder joints of the component terminals.
A5-5026 Power Supply Board Restoration
This board can be serviced in place. There are only four capacitors to change.
Here is the board prior to restoration.
C1 is rated 100 uF / 63 V and was changed with a Nichicon KZ MUSE series 100 uF / 100 V modern capacitor. C2 and C3 were originally rated 330 uF / 63 V and were changed with Nichicon KZ MUSE series rated 330 uF / 100 V. C4 was a 47 uF / 50 V capacitor and was replaced with the same rating Nichicon KZ MUSE series modern part.
And after the job.
I have renewed the solder joints of the component terminals.
A5-5061 Switches Board Restoration
On this board there are no electrolytic capacitors and no transistors. So nothing to replace. But I decided to restore the solder joints for future proofing. I am pleased with the results.
Aftermath
Old parts.
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