On the basis that someone here will know where I should ask, I've a 20 year old hi-fi amplifier (Aiwa A60) that's playing up and I need some guidance on what might be wrong. I suspect electrolytic capacitors, but would really need access to a circuit diagram.
Is there someone here who is currently active in audio electronics and could point me towards the right forum please.
Thanks Rob
sci.electronics might be of use, but you could ask here as well. You probably won't get a cct. diagram, but you might not need one. What do you mean by 'playing up'?
J^n
If you give details of the fault you might get help here. Have you Googled for a circuit diagram? You might have to pay for one, of course. But unless it's something special it's usually possible to fix amps without.
Well not currently, but I used to design the buggers 20 years ago.
Wosup with it?
not nearly enough info to help. Re cct diags, they're usually not needed. If you want one, google's your friend.
NT
sci.electronics.repair may help (if you have already done the googling).
Well thanks for your offers, guys. I hang around here quite a bit and it always astounds me the range and depth of knowledge that can be tapped into. But having said that I was quite expecting to have to go elsewhere.
Anyway, here we go. Firstly I've been unable to track down a circuit diagram on the net. Secondly I'm a retired electronics engineer so in theory should be able to sort it myself, but I've only a dvm or two - no 'scope and that would be my tool of preference for this.
The amplifier and receiver are my workshop music. If I switch both off, the receiver loses the station tuning, and despite the lack of logic, if I switch the receiver off only, the station tuning is retained. A week ago I went into the workshop and the loudspeakers were giving a low volume sound like very low repetition rate motor boating - cycle time was remarkably near 1Hz. Nothing would change it so this was being generated after the pre-amp stage. When the receiver was switched on the output was quite heavily distorted but as time went on - 30 minutes at least, this distortion disappeared.
So the amplifier on it's own ' motor-boats', add an input and the output is initially distorted but is clear after about 30 minutes.
Bit odd - any ideas ?
Thanks Rob
Service Manual Aiwa SA-A60 Amplifier,ORIGINAL ebay item #360100377167
I don't do audio but it sounds like the power supply dustbin capacitors are f*****. Classic clue seems to be the initial distortion clearing after 30 minutes. Indicative of failing capacitors chemically reforming themselves.
failing electrolytic.
Strip it completely and replace the ruddy lot.
Is the tuning digital?
If its losing digital info, its probably a battery thats gone as well.
Motor boating means its unstable, oscillating, and that's usually caused by failing decoupling capacitors. To find out what's wrong just piggy back all the supply chain caps, one by one, until it clears up.
Distortion is often caused by instability. But if fixing that doesnt undistort it, you'll be looking at a bias voltage somewhere thats varying when it shouldnt be. A high reistance meter should track that down.
Re sillyscopes, I only rarely used them, a multimeter is plenty for most jobs. You can generally get a good idea of where things are going wrong by applying a finger or a signal to various points to see where its coming through clean & where its not. You can also use a little high R input amp to test various points to see where it distorts. I doubt you'll need a scope or a diagram - though no guarantees.
Is it misbehaving the same on both channels or just one? That's a major clue.
NT
Thanks everyone. I've just looked at Ebay - only 10 hours after you posted Adrian, and there's nothing there ? But thanks for that tip as I hadn't thought of looking on Ebay.
Sounds like I'd better start with the 'dump' capacitors as 'JJ Designs' suggests. I hadn't thought of the chemical reformation with time.
Thanks Rob
Sorry Adrian - found it after all - thanks Rob
Bit odd as you say. Unless you've a particular interest in tracking down the problem, the simplest solution (for workshop music) is to buy a replacement receiver on eBay. Some outstandingly good twentieth century kit can be had for remarkably little. And for even less if you can collect.
The loss of tuning on tuners of this era normally mean that the the supercap has failed. These are usually about 0.5 or 1 Farad capacitors. I is just possible that it uses a battery but my money is on supercaps.
RS sell them. i've just checked and see they do them up to 50F!! now.
Bob
Like you say, no logic there, but are these seperates, or integrated in some way? Do they have independant mains supplies?
MBQ
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