Vintage Audio
this section covers some restoration work that I did on my vintage HI-FI gear
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Article #1 | 10:00 PM Sunday 03/01/2016

AKAI AA-5210 #1: Introduction

This is one of my two identical amplifiers that I use in my study.

The electrical characteristics of this small amplifier might look conservative at first. But I assure you, it is a true performer. Mine was playing music for almost seven years on a daily basis, at least eight hours per day. And it was great. Now I decided to restore it because I can smell a weird strong electrolyte odor from the venting grilles. This is not a good sign. It means that one or more capacitors have leaked and valuable transistors are at risk. Otherwise, it still sings music.

If you want to see its brother passing through the same restoration process, then check out its page: AKAI AA-5210 #2.

Article #2 | 11:00 PM Sunday 03/01/2016

AKAI AA-5210 #1: Technical Data

This amplifier has the following technical characteristics.

TECHNICAL PARAMETERS
ParameterValue
Continuous RMS power (both channels)15 W + 15 W (8 Ω at 1,000 Hz)
Total Harmonic Distortion<0.5% (at rated output)
IHF power bandwidth (each channel driven at 8 Ω)15 Hz - 80,000 Hz
Frequency Response (at normal listening level)20 Hz - 50,000 Hz
Load Impedance4 Ω - 16 Ω
SemiconductorsTransistors: 23 / Diodes: 8
Power Voltage100 V, 117 V, 220 V, 240 V, at 50/60 Hz
Power Consumption120 W (max)
Dimensions / Weight108 mm (H), 430 mm (W), 290 mm (D) / 7.2 kg

Article #3 | 12:10 PM Tuesday 05/01/2016

AKAI AA-5210 #1: Parts List

I have assembled a parts list for this amplifier. My restoration touches some of the original transistors. Normally the original transistors contribute to the authentic AKAI sound. But modern equivalents are better in any aspects. I am also interested in exchanging the electrolytic capacitors. So this is what you will find listed below.

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. Where I found appropriate, I have chosen a film capacitor replacement instead of an electrolytic. My reasons are reliability in time. Less electrolytic capacitors, less time-ticking bombs.

Descriptions and Parts Listings

The Power Amplifier Block is coded 96-5008 and is located in the bottom-right part of the steel chassis. You will recognize it by the power transistors which are mounted on an aluminum radiator.

Power Amplifier Block (96-5008)
IdentifierSchematicRecommended
1-C12.2 uF / 50 V
1-C1b2.2 uF / 50 V
1-C2100 uF / 50 V
1-C2b100 uF / 50 V
1-C52.2 uF / 80 V
1-C5b2.2 uF / 80 V
1-C7100 uF / 6.3 V100 uF / 16 V
1-C7b100 uF / 6.3 V100 uF / 16 V
1-C91000 uF / 25 V AUDIO
1-C9b1000 uF / 25 V AUDIO
1-C11220 uF / 35 V
1-C11b220 uF / 35 V

The Tone Control Block is coded A5-5029 and is located in the front-center region of the steel chassis, next to the tone shaping potentiometers. For an easy maintenance access, you need to extract this board. Or you could work your way through the bottom of the amplifier chassis after you remove the switches printed circuit board.

Tone Control Block (A5-5029)
IdentifierSchematicRecommended
2-C147 uF / 50 V
2-C1b47 uF / 50 V
2-C547 uF / 6.3 V47 uF / 25 V
2-C5b47 uF / 6.3 V47 uF / 25 V
2-C64.7 uF / 25 V4.7 uF / 50V
2-C6b4.7 uF / 25 V4.7 uF / 50V
2-C1010 uF / 25 V10 uF / 50 V
2-C10b10 uF / 25 V10 uF / 50 V
2-C12100 uF / 6.3 V100 uF / 25 V
2-C12b100 uF / 6.3 V100 uF / 25 V
2-C1347 uF / 50 V
2-C13b47 uF / 50 V
1-C142.2 uF / 25 V
1-C14b2.2 uF / 25 V

The Equalizer Block is coded A5-5028 and implements the Phono preamplifier and the RIAA correction curve. You can find it in the front-right part of the steel chassis, next to the Tone Control Block board. In order to operate changes, you need to extract this board too. Or you could work your way through the bottom of the amplifier chassis.

On this board the capacitors are listed for both channels.

Equalizer Block (A5-5028)
IdentifierSchematicRecommended
3-C1100 uF / 16 V100 uF / 25 V
3-C2100 uF / 16 V100 uF / 25 V
3-C31 uF / 25 V1 uF / 50 V FILM
3-C41 uF / 25 V1 uF / 50 V FILM
3-C52.2 uF / 25 V
3-C62.2 uF / 25 V
3-C710 uF / 25 V10 uF / 50 V
3-C810 uF / 25 V10 uF / 50 V
3-C91 uF / 50 V1 uF / 50 V FILM
3-C101 uF / 50 V1 uF / 50 V FILM

The Power Supply Block is coded A5-5026 and occupies the bottom-center of the steel chassis next to the power transformer. You recognize it by the four rectifier diodes.

For the electrolytic capacitors on this board, you need to order only once.

Power Supply Block (A5-5026)
IdentifierSchematicRecommended
5-C1100 uF / 63 V100 uF / 100 V
5-C2330 uF / 63 V470 uF / 100 V
5-C3330 uF / 63 V470 uF / 100 V
5-C447 uF / 50 V47 uF / 63 V

The construction of this amplifier is straightforward and poses no problems for the restoration.

As always, let me throw a piece of advice. Do not hurry, take your time and do the job once. And do it well.

Article #4 | 11:36 AM Monday 06/11/2017

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

I should begin by saying that working on this amplifier 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 amplifier, 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 323 degrees Celsius is sane for these 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.

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 moder 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.

Article #5 | 06:53 PM Thursday 09/11/2017

AKAI AA-5210 #1: Impressions

So how does it sound? Like an AKAI AA-5210, obvious. It doesn't resemble to anything else that I have listened so that I could make a comparison. On this unit however both low-end and high-end of the spectrum were rendered very poor. Now everything is as it should be. Loud and clear. Midrange frequencies were laid back and there is no change about this. I think this is the circuit topology. This is how it was designed. It is not bad at all. But different.

I don't know exactly what to do with this little amplifier. Where to position it and what service it will do. Until I find some way to put it to good use, it will rest in the corner. Previously it was my study amplifier making a nice duet with it's identical brother. In the meantime it was replaced by the Sansui AU-7500. So the AKAI pair is now having a rest.

Overall I declare the restoration a success. Until the next maintenance, this topic is closed.

Copyright © 1998- Alexandru Groza