Hi All,
So I'm gonna get this out of the way now, I'm new to this forum, electronics in general (I'm in engineering and have a basic understanding of circuits, but zero experience actually working with them. Just theoretical knowledge) and to this amplifier. So my questions may or may not be redundant/common knowledge. Additionally, my apologies for the length of this post.
I purchased an Akai AA-920 amplifier from my father around 6 months ago, brought it home and just started using it. It ran fine, he hadn't used it more than twice in the last 25 years but I'm more than happy to. I use it for my phonograph, video game console and music system. It runs pretty well, but... there are a couple issues, and as I bought it from my father (his one stipulation was that I never sell it as he bought it brand spankin' new in the 70's for over 500$) I want to be able to take good care of it.. you don't see a lot of them around anymore.
So, as i mentioned earlier, it works, but there ARE a couple issues and I'd love to diagnose them before taking it... somewhere... to get looked at. The issues are:
-One of the lamps in the front face is out (no idea where to purchase or how to install)
-general buzzing depending on volume (lower volumes give more buzz, also the left speaker cuts in and out with "out" leaving about 10% volume and 20% clarity)
-an EXTREMELY dusty interior (apart from a can of compressed air, how am I to clean the inside of this without damaging any internal workings?)
-2/3 of the speaker ports in the rear of the amplifier no longer work (I have no idea how to fix them)
-there may be other issues, I just haven't honestly explored it too much. I bought it, plugged what I was using it for into it, and went to town.
My apologies for any perceived neediness, like I said I'm new to this side of electronics and I REALLY don't want to mess something up in the process of trying to bring this thing back to it's former glory. If anyone needs, I can gladly post pictures of it as well.
Thanks in advance,
Justin
P.S. I'm located in Saskatchewan, Canada, so as far as I've found there's nowhere I can purchase parts/talk with someone who knows this amp in town. Any help is greatly appreciated.
So I'm gonna get this out of the way now, I'm new to this forum, electronics in general (I'm in engineering and have a basic understanding of circuits, but zero experience actually working with them. Just theoretical knowledge) and to this amplifier. So my questions may or may not be redundant/common knowledge. Additionally, my apologies for the length of this post.
I purchased an Akai AA-920 amplifier from my father around 6 months ago, brought it home and just started using it. It ran fine, he hadn't used it more than twice in the last 25 years but I'm more than happy to. I use it for my phonograph, video game console and music system. It runs pretty well, but... there are a couple issues, and as I bought it from my father (his one stipulation was that I never sell it as he bought it brand spankin' new in the 70's for over 500$) I want to be able to take good care of it.. you don't see a lot of them around anymore.
So, as i mentioned earlier, it works, but there ARE a couple issues and I'd love to diagnose them before taking it... somewhere... to get looked at. The issues are:
-One of the lamps in the front face is out (no idea where to purchase or how to install)
-general buzzing depending on volume (lower volumes give more buzz, also the left speaker cuts in and out with "out" leaving about 10% volume and 20% clarity)
-an EXTREMELY dusty interior (apart from a can of compressed air, how am I to clean the inside of this without damaging any internal workings?)
-2/3 of the speaker ports in the rear of the amplifier no longer work (I have no idea how to fix them)
-there may be other issues, I just haven't honestly explored it too much. I bought it, plugged what I was using it for into it, and went to town.
My apologies for any perceived neediness, like I said I'm new to this side of electronics and I REALLY don't want to mess something up in the process of trying to bring this thing back to it's former glory. If anyone needs, I can gladly post pictures of it as well.
Thanks in advance,
Justin
P.S. I'm located in Saskatchewan, Canada, so as far as I've found there's nowhere I can purchase parts/talk with someone who knows this amp in town. Any help is greatly appreciated.
This thread clearly belongs on another "board". Everything about the AA-920 "schematic" indicates solid state (SS). This "board" is for vacuum tube stuff, not "sand".
In any event, electrolytic capacitors literally dry out, over time. Tubes or SS, when dealing with something that old, the 1st order of business is replacement of all electrolytic capacitors. Dried out 'lytics can easily cause the bad sound you hear.
With unit unplugged, blow all loose crud out. Then use moistened paper towels to attack stubborn unpleasantness. Make absolutely sure things have dried out, before attempting power on.
In any event, electrolytic capacitors literally dry out, over time. Tubes or SS, when dealing with something that old, the 1st order of business is replacement of all electrolytic capacitors. Dried out 'lytics can easily cause the bad sound you hear.
With unit unplugged, blow all loose crud out. Then use moistened paper towels to attack stubborn unpleasantness. Make absolutely sure things have dried out, before attempting power on.
Attachments
What you have is not an amplifier but a receiver.
The Akai AA-920 is a combination of an AM/FM-tuner and an amplifier.
The 920 is the smallest in the series AA-920, AA-930 & AA-940.
One servicemanual covers all and it's available free from here:
Akai AA-920 - Manual - Stereo Receiver - HiFi Engine
You need to signup to download but it's free.
The output amplifier in the 920 is very much different from the other, bigger models and the 920 doesn't have a speaker protection circuit/relay that may have otherwise presented problems like the ones you're experiencing.
2/3 of the speaker ports not working..?
Well, it's a stereoamplifier so you have 2 channels to begin with, not 6.
The 2 channels are just split into 6 outputs enabling the use of sets of speakers selected individually or combined by use of the speaker selection switch.
So, I would say you have one channel down or an extremely corroded speaker selection switch. Both are equally possible.
Eli Duttman is of course right about re-capping this mid 70'ies set. Most of the electrolytic capacitors are likely long gone, causing all kinds of instability and bad sound quality in general. You either decide to replace all, which I kind of favour, or you get hold of an ESR-meter to measure what's still working and what's not. Use of this kind of meter relays somewhat on experience to determine what's actually defective and what's not imho. Since you don't have that experience I recommend the brute force attack.
Then there's the problem with D1 / STV-3H bias stabilizing triple-diode in the output amplifier. Famous for being really unstable causing output transistor failure.
Needless to say all switches and potentiometer should be cleaned.
Caig DeoxIT is preferred for this by many.
The Akai AA-920 is a combination of an AM/FM-tuner and an amplifier.
The 920 is the smallest in the series AA-920, AA-930 & AA-940.
One servicemanual covers all and it's available free from here:
Akai AA-920 - Manual - Stereo Receiver - HiFi Engine
You need to signup to download but it's free.
The output amplifier in the 920 is very much different from the other, bigger models and the 920 doesn't have a speaker protection circuit/relay that may have otherwise presented problems like the ones you're experiencing.
2/3 of the speaker ports not working..?
Well, it's a stereoamplifier so you have 2 channels to begin with, not 6.
The 2 channels are just split into 6 outputs enabling the use of sets of speakers selected individually or combined by use of the speaker selection switch.
So, I would say you have one channel down or an extremely corroded speaker selection switch. Both are equally possible.
Eli Duttman is of course right about re-capping this mid 70'ies set. Most of the electrolytic capacitors are likely long gone, causing all kinds of instability and bad sound quality in general. You either decide to replace all, which I kind of favour, or you get hold of an ESR-meter to measure what's still working and what's not. Use of this kind of meter relays somewhat on experience to determine what's actually defective and what's not imho. Since you don't have that experience I recommend the brute force attack.
Then there's the problem with D1 / STV-3H bias stabilizing triple-diode in the output amplifier. Famous for being really unstable causing output transistor failure.
Needless to say all switches and potentiometer should be cleaned.
Caig DeoxIT is preferred for this by many.
Moved to Solid State
Hi Justin,
I'm familiar with working on these, and from your comments I would suggest that you take it into a good audio repair shop for repair. Not a store for new product, and not a TV service place. The repair tech you want will likely be in his 50's or older and may work from home.
Do not let someone who "recaps" equipment. These folks are typically laymen who buy capacitor kits, or from stores. They don't know what they are doing in all honesty. I hate cleaning up after one of these geniuses after they've done their work. Note that this is a labour intensive process and will cost a lot.
Get your receiver repaired and the good tech will change capacitors as required. After you live with the set for a time you can elect to have this done. Wait for it to have another issue first.
So, take it easy and one step at a time. Do some research on local repair shops. Is Commercial Electronics near you? They were pretty good as I recall. I met them on a course on Nakamichi. If your tech or shop was authorized warranty for high end brands of equipment (and still might be), they would be a good choice. Keep in mind that there are many horrible shops and technicians out there.
If you see their work area, expect to see a good stock of parts, like all commonly available resistors and capacitors. Look for semi-modern test equipment and a controlled temperature soldering station. If you see a collection of replacement semiconductors (ECG, NTE, etc) run away! Someone who cares about their work will probably have a Tektronix or HP/Agilent/Keysight oscilloscope, and other equipment. Fluke meters are popular, so add them to the above list.
Best, Chris
I'm familiar with working on these, and from your comments I would suggest that you take it into a good audio repair shop for repair. Not a store for new product, and not a TV service place. The repair tech you want will likely be in his 50's or older and may work from home.
The bias sensing diode is not unreliable at all. It is prone to being damaged by those technicians you shouldn't use. These temperature sensing diodes were used by many manufacturers through that time period and are commonly found in many amplifiers. The most common failure is that the lead breaks off right at the body and shouldn't be a concern unless someone has been "playing" inside. This is why a professional should work on it instead of a friend or guy who "knows electronics".
Do not let someone who "recaps" equipment. These folks are typically laymen who buy capacitor kits, or from stores. They don't know what they are doing in all honesty. I hate cleaning up after one of these geniuses after they've done their work. Note that this is a labour intensive process and will cost a lot.
Get your receiver repaired and the good tech will change capacitors as required. After you live with the set for a time you can elect to have this done. Wait for it to have another issue first.
So, take it easy and one step at a time. Do some research on local repair shops. Is Commercial Electronics near you? They were pretty good as I recall. I met them on a course on Nakamichi. If your tech or shop was authorized warranty for high end brands of equipment (and still might be), they would be a good choice. Keep in mind that there are many horrible shops and technicians out there.
If you see their work area, expect to see a good stock of parts, like all commonly available resistors and capacitors. Look for semi-modern test equipment and a controlled temperature soldering station. If you see a collection of replacement semiconductors (ECG, NTE, etc) run away! Someone who cares about their work will probably have a Tektronix or HP/Agilent/Keysight oscilloscope, and other equipment. Fluke meters are popular, so add them to the above list.
Best, Chris
About this we disagree. I have come across this device in other brands as well and in my experience they DO break down from other problems than physical abuse.
If they were the initial cause of problems or they got slammed in the process is of course hard to say.
Other than that I'm all with Chris.
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