Akai AA-1150 problem

[Chico_13]

I just bought an Akai AA -1150 receiver and initially it was near perfect.. however, after a few days of playing it, the protection circuit cut out the speakers (in stereo mode) at 20% volume.. I switched it to Mono and both speakers worked fine at any volume.. I tested the DC offset voltages and they were very low at 9MV.. and that was great. I disconnected each speaker (one at a time) and tested it - the protection circuit didn't cut out the speakers at any volume .. I am stumped at what is the cause. I guess I will just have to remove the power amp board to check the protection circuit components - it will be a big job as the Amp is tucked between the Power supply and the Heat sink and I will have to find a wire wrapping/ unwrapping tool first of course. Any suggestions? thanks
Paul

 

[shrtrnd]

My first suggestion is that if you bought it new from a store, take it back under warranty.
My second suggestion is to check your speaker specifications.
It sounds to me like maybe your speakers are not rated to handle the output of your receiver's amplifier.

 

[Chico_13]

No I didn't buy it new..My speaker connections are fine and I use Paradigm Mid-size Speakers 7SE that are rated for 100 Watts.. The Akai puts out 50 watts/c. I am almost certain that the Protection circuit components are at fault. I have many years in the electronic field but this problem stumps me. I have five other high end receivers that I use the speakers with without any problems.

 

[shrtrnd]

I suppose your guesstimate might be right, but it doesn't make sense to me that individually (one speaker at a time) speaker prrotection does not kick-in. But when both speakers are used, protection engages.
My first thought is that perhaps you have your polarity at odds between the two speaker connections. Check that and see if one speaker connection is wired backwards from the other.
Frankly, I'd check both speaker connections very closely. I have some Acoustic Research speakers that geve me a problem once with a loose connection at the speaker housing.
I am of the opinion that this is a load problem at the speaker output. It may be a electronic problem with your internal speaker protection circuit as you suspect, but I'd thoroughly check my speaker/load set-up,
before I went for a circuit problem. Are you SURE one of those speakers isn't bad?
If you convince yourself the problem is internally within the receiver amplifier, don't forget to check the power output transistors as they are most likely to 'leak'/fail due to high stress.

 

[Chico_13]

I tried connecting just one input (AUX from a CD Player) at a time and the protection circuit kicked in (in Stereo mode) at 20% volume.. each channel was the same. When I switched to Mono I could turn the volume up to more than 50% with out it cutting off the speakers ???? The speakers themselves seem to be good as I don't have this problem with other Amplifiers. I have checked the ground connections on the amp and they are good.. I tested the DC offset voltages and they were very low at 9MV which I believe are good - they say 25 MV or less is good.

I can't figure out how to post a photo that is from my computer?? I wanted to show the power amp location????
Your help is appreciated shrtrnd

Paul

 

[shrtrnd]

I think the next step is to Google your model number and see if you can find a free schematic for your receiver.
Looking at a picture is often helpful, but a schematic is like gold when troubleshooting.

 

[Chico_13]

Thank you shrtrand I have now found the problem.. it turns out there were bad connections on a speaker selection box I am using.. I decided to wire the speakers directly to the Akai amp and Voila !
your help was greatly appreciated.
The sound that the Akai produces is equal if not better than the Pioneer SX-780 and Marantz 2230 that I have.

Many thanks and regards for helping me resolve this.

Regards,

Paul

I do have the schematic and the service manual for future use of course.. ha ha.

 

[shrtrnd]

Glad you found the problem.
If we'd known you were using an independent speaker selection box, that probably would have been high on the 'things to check first' list.
The symptom seemed unusual for a reciever/amplifier internal issue.
I know it took a lot of work and frustration to isolate the problem, but we appreciate people who don't easily give-up.
It's rewarding to hear that you took the time and effort necessary to effect this repair.
Hope you get a lot of years of enjoyment from your system.

 

[Chico_13]

I really should have used the old adage "Simple to Complex" as I have done for 42 years in the Electronics Industry..But when one is 77 , one does forget things at times..
Thanks again for your help and hope that I may help someone else in the future..
Take care shrtrnd

Paul

 

[shrtrnd]

We can use all the insight we can get. Some of us like to think we know everything sometimes, but occasionally we get a question that stumps us.
We can use some of those years of experience here. You'll probably find if you check here once in a while, that you know
something we can only speculate about. There are some pretty knowledgable people on this site, and we all like to help people asking questions when we can.
Hope to see you back here with advice and information when you can spare the time.
Dennis