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am2800 noise

T

Thunderknob

New Member
Just joined Audiokarma today I effort to fix my amp. My am2800 hasn't been used for years. I set it up again recently, but it has developed issues.
Everything was operating fine until it started pegging the right side meter with intermittent full volume static. Even with the volume turned off, every ten seconds, or so, it makes extremely loud crackling and the right side meter flickers and pegs momentarily. I took the cover off and I can see and hear the relay with the points flicking and clicking.
I had trouble with the on/off button sticking, last year. I took it apart and freed the stickiness and resurfaced the contacts. I saw a video about how a bad switch was causing the red light to come on, but not power up completely. My switch is fine now, I am sure. I've rebuild plenty of switches. Also, I noticed the meter light is burned out.
The amp has never been cleaned or serviced. It's not dirty. Nothing gets warm. I don't know what's wrong. Hopefully someone out there has seen this specific problem, the intermittent full volume crackling and the flickering of the right side meter. I have access to a volt meter that will read millivolts, but I haven't checked the adjustments shown on Uribe yet. I haven't used that spray cleaner yet either. Everything was operating correctly, until this major noise issue. It's not a tuning problem, I pretty sure. Something has failed. I'm not an electronic geek, but I'm ok at soldering. Help!
 
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Thunderknob said:
Just joined Audiokarma today I effort to fix my amp. My am2800 hasn't been used for years. I set it up again recently, but it has developed issues.
Everything was operating fine until it started pegging the right side meter with intermittent full volume static. Even with the volume turned off, every ten seconds, or so, it makes extremely loud crackling and the right side meter flickers and pegs momentarily. I took the cover off and I can see and hear the relay with the points flicking and clicking.
I had trouble with the on/off button sticking, last year. I took it apart and freed the stickiness and resurfaced the contacts. I saw a video about how a bad switch was causing the red light to come on, but not power up completely. My switch is fine now, I am sure. I've rebuild plenty of switches. Also, I noticed the meter light is burned out.
The amp has never been cleaned or serviced. It's not dirty. Nothing gets warm. I don't know what's wrong. Hopefully someone out there has seen this specific problem, the intermittent full volume crackling and the flickering of the right side meter. I have access to a volt meter that will read millivolts, but I haven't checked the adjustments shown on Uribe yet. I haven't used that spray cleaner yet either. Everything was operating correctly, until this major noise issue. It's not a tuning problem, I pretty sure. Something has failed. I'm not an electronic geek, but I'm ok at soldering. Help!
Click to expand...
A few obvious spell check things, sorry.
 
Welcome aboard! What brand is the amp? It sounds like you possibly have a noisy transistor or two. Or, it could be a poor solder connection.
 
UncleAng said:
Since it's almost 50 years old you may need a new relay.
Click to expand...
Akai am2800. No way to really see inside relay without removing it. I can't even get the cover off to clean it. Probably no way to test it. Surely someone has see this problem, specific to am2800, without taking a guess. The relay looks like a real bother to replace for an amateur.
 
redk9258 said:
Welcome aboard! What brand is the amp? It sounds like you possibly have a noisy transistor or two. Or, it could be a poor solder connection.
Click to expand...
Akai am2800. Pretty famous amp, evidently. Surely someone has seen this exact problem before, in an am2800 and can tell me how to test something to be sure. True, I haven't looked at any manuals yet. Just utube.
 
I believe the relay is dropping in and out because of excessive DC voltage on the outputs. Try measuring DC offset on the faulty channel. Pegging the power meter and crackling through the speakers sounds more like a transistor issue to me than relay, but I'll let others more educated chime in on that one
 
If you feel comfortable opening the unit up and trying to find the issue. I'd suggest either diagnostic freeze spray or a can of compressed air (flipped upside down) will do the same thing. You spray the transistors on the amp board one by one and if any trigger the problem that's likely your culprit. Personally, I would use a pair of headphones I didn't care about for this.
 
Dan13105 said:
I believe the relay is dropping in and out because of excessive DC voltage on the outputs. Try measuring DC offset on the faulty channel. Pegging the power meter and crackling through the speakers sounds more like a transistor issue to me than relay, but I'll let others more educated chime in on that one
Click to expand...
By the sound it makes, I'd say there is excessive voltage somewhere. I gotta borrow a good volt meter and do that 30 millivolt tests and the output tests. I hope that leads in the right direction.
 
alowe0110 said:
If you feel comfortable opening the unit up and trying to find the issue. I'd suggest either diagnostic freeze spray or a can of compressed air (flipped upside down) will do the same thing. You spray the transistors on the amp board one by one and if any trigger the problem that's likely your culprit. Personally, I would use a pair of headphones I didn't care about for this.
Click to expand...
Diagnostic freeze spray? I never heard if it. That's why I'm on this site; to learn something. I would like to understand what the function of each part is. I need to find a service manual, if there is one. To clarify, there were days when it worked perfectly all day, and the next day, it would blast intermitent full volume scratching. And then later it would be fine again. Now, all it does is jump up and down on the right gauge and make intermittent full volume noise that is unaffected by any knob, except the speaker choise, and the volume knob has no effect. It's unusable. I gotta borrow that good volt meter soon. I'm not afraid to tackle it. I just don't want to spend much money on it, even though it could be potentially valuable.
 
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Thunderknob said:
Diagnostic freeze spray? I never heard if it. That's why I'm on this site; to learn something. I would like to understand what the function of each part is. I need to find a service manual, if there is one. To clarify, there were days when it worked perfectly all day, and the next day, it would blast intermitent full volume scratching. And then later it would be fine again. Now, all it does is jump up and down on the right gauge and make intermittent full volume noise that is unaffected by any knob, except the speaker choise, and the volume knob has no effect. It's unusable. I gotta borrow that good volt meter soon. I'm not afraid to tackle it. I just don't want to spend much money on it, even though it could be potentially valuable.
Click to expand...
the unit uses 2sc1312 transistors. they get noisy. they need replaced.

i've never worked on an am2800, only my am2600 and it is a nice amp.

i really wouldn't recommend using it as a first unit to work on. you know it could be valuable, one sold last month for $850+shipping last month.

the pcbs have no silk screening on them so you must know how to translate the boardview in the service manual to the pcb in reverse to locate parts. much attention must be paid and taking alot of pics are required for reference.

there is another thread going on right now on the am2800 in this section. go follow along.

but if you insist on doing it,

here's the service manual:

Elektrotanya for electronics experts

Electronics forum for electronics experts to repair defective appliance.
elektrotanya.com elektrotanya.com

you need to build a dim bulb before you get into it. there are plenty of threads on that, just use the search feature.

there are 3 2sc1312 per channel after the volume control, in the tone section. read up on freeze spray and how to use it and spray each one while it's acting up. if it stops acting up, you've found the culprit.



i suggest to buy something cheap to learn on. acquire some tools and experience first.
 
If one of the experts disagrees with me, take their advice over mine. In my opinion that definitely sounds like a noisy transistor. The freeze spray I use is "Techspray 1672-10S" you can find it on Amazon, among many other sites. Normally I'd send you over to HIFI-Engine for service manuals, but they're closed to new member registrations. If you do a Google search for "Elektrotanya Akai AM-2800 service manual" you'll find yours.
 
It's fixed! I borrowed a fluke 29 meter, and did the checks. The idle current was way off. One high, one low. While I was adjusting it, (it responded well), the relay stopped the chattering. I connected everything back up and, voila, it's working perfectly, except the meter light is burnt out. Easy fix. I can't believe a simple adjustment was all it took to fix that ear shattering crackle. Hope it stays fixed!
 
I've had this am 2800 for decades. Only use it during summer. Sometimes it will work excellent. Sometimes it cuts out and blasts scratchy static at full volume that no knob can control. This summer when turning it on, it played music for a few seconds, then went to intermittent high volume static.
I don't know much about it. The big clear plastic box with four sets of points in it keeps sparking on and off intermittently, sometimes with a really big spark! When the amp is turned on, the points open after a second, then the noise begins. It is steady low static with frequent blasts of full volume static. The right side meter pegs when doing this. The points will close for a few seconds of silence, then spark open again bringing noise. This problem has been coming and going for years, now it won't go away. Last year I borrowed a multi meter and set the tune up adjustments. That cured it's problem last year. This year they have no effect. It's probably beyond my ability, but I would give it a shot if I had a clue.
 
Thunderknob said:
I've had this am 2800 for decades. Only use it during summer. Sometimes it will work excellent. Sometimes it cuts out and blasts scratchy static at full volume that no knob can control. This summer when turning it on, it played music for a few seconds, then went to intermittent high volume static.
I don't know much about it. The big clear plastic box with four sets of points in it keeps sparking on and off intermittently, sometimes with a really big spark! When the amp is turned on, the points open after a second, then the noise begins. It is steady low static with frequent blasts of full volume static. The right side meter pegs when doing this. The points will close for a few seconds of silence, then spark open again bringing noise. This problem has been coming and going for years, now it won't go away. Last year I borrowed a multi meter and set the tune up adjustments. That cured it's problem last year. This year they have no effect. It's probably beyond my ability, but I would give it a shot if I had a clue.
Click to expand...
Check the power switch. Sometimes they will arc and produce that noise. One would think the points, contacts would soon completely burn and either weld together or completely quit conducting but sometimes they will arc for some time. I've seen it but might not be the case here. Just that I've seen it and more than once, other models and brands.
 
Merged 2 threads on the same radio into a common thread.
 
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