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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 15th Oct 2018, 5:02 pm   #1
Alf Fisher
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Default Yamaha CA-1010 Stereo Amp

Hi folks,

I have been asked to look at this amp that exhibits the worst kind of problem - the intermittent one. Occasionally the left channel output will go extremely distorted like a total bias failure or a push-pull stage that has lost its push!

Whilst I have had it, it hasn't done its worst and the only thing I am suspecting at the moment is the few little blue bead tantalum caps on the preamp board. I know that in the 1970s tantalum caps were reckoned to be the best available and many military equipments used them but after 40 years they are causing trouble.

Has anyone else experienced this kind of problem and I'm wondering if replacing them all might be my best option.

Cheers, Alf
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Old 15th Oct 2018, 9:49 pm   #2
kevinaston1
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Default Re: Yamaha CA-1010 Stereo Amp

No.

Rather than replacing things you suspect, find the fault. With the amplifier playing nicely, probe around all the circuitry with a non-conductive stick (an old toothbrush is ideal); if the fault is a dry joint, this will show it up.

If nothing is found, it is probably temperature related. Gently heat the circuitry with a hair dryer. When the fault occurs, carefully give each component in that area a blast of freezer spray to locate the offender.

If you are unsure where the fault is after you have found a way to provoke it. On the back of the amplifier is a switch on the left marked coupler. Place this in the OFF position , and cross couple the adjacent phono sockets left out to right in, and vice versa. Now, if the fault was originally on the left, but it changes to the right, you have a fault on the left pre-amplifier section.

I was taught time and time again in training, when you have an intermittent fault; disturb the unit as little as possible, and trace the fault using your brain. If you start disturbing the unit, the intermittent fault will disappear for months; but it will eventually bounce back on you.


By carefully tracing the fault down, you will find the offending component.



Kevin
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Old 15th Oct 2018, 10:18 pm   #3
paulsherwin
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Default Re: Yamaha CA-1010 Stereo Amp

The first thing to do is to check for dry joints, particularly around the output protection relay and associated circuitry if present. I agree that randomly changing capacitors is unlikely to achieve anything. This is unlikely to be a capacitor fault.
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Old 15th Oct 2018, 10:20 pm   #4
PJL
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Default Re: Yamaha CA-1010 Stereo Amp

How confident are you that the fault was not in other parts of the audio setup?
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Old 16th Oct 2018, 1:04 pm   #5
Telegraph-Hill
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Default Re: Yamaha CA-1010 Stereo Amp

Hi there,
I do own the smaller brother CA810. My one had multiple problems like noisy pre Amp Transistors (2SC844), faulty diodes in the power amp module, old capacitors and many more. The first step is to look if this is a pre amp problem. Usually when there is a problem with the power amps the protection circuit will kick in. Maybe it is a good idea to check the pre amp boards with cooling spray or tapping the boards to see if the problem can be recreated. But it is all a look in the glass bowl, sorry, Oliver
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Old 16th Oct 2018, 2:16 pm   #6
FIXITNOW
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Default Re: Yamaha CA-1010 Stereo Amp

only see one sim model CA-1000 one channel was going off with distortion, fault was in the preamp. Replacing the transistors on the filter board behind the switches cured it.
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Old 16th Oct 2018, 2:43 pm   #7
paulsherwin
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Default Re: Yamaha CA-1010 Stereo Amp

If there is a known problem with these preamp transistors then it should be easy enough change them with general purpose types - 2N3904, 2N3906 etc. If that clears the problem then you can look at sourcing some specialist types if necessary.
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Old 16th Oct 2018, 5:51 pm   #8
Alf Fisher
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Default Re: Yamaha CA-1010 Stereo Amp

Thanks for all your suggestions guys. The trouble is the fault hasn't shown itself since I have had the amp. I've done the usual prodding in an attempt to find a dry joint but I suppose the fault could be in the tuner! I'll try the freezer spray to see if that will cause the fault to reveal itself.

Alf
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Old 16th Oct 2018, 6:17 pm   #9
bikerhifinut
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Default Re: Yamaha CA-1010 Stereo Amp

What springs to mind here is, did you hear the fault in the context of the owners system?
Just that since you have had it, you can't provoke or find a fault?
I'd be thinking of an interconnect fault either working loose or a dry joint inside an RCA plug or any other mechanical fault that could cause a noisy/high resistance connection? or maybe speaker wires becoming loose at the back or even at the loudspeaker?
And again, did this fault appear using all input sources or just the one? I'f on one source only then you have to suspect the source component or its connection to the amp.

Just my take on it. Intermittent faults are the worst to track down as we all know.

A.
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Old 17th Oct 2018, 12:31 pm   #10
micheal
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Default Re: Yamaha CA-1010 Stereo Amp

Check speaker relay contacts these are silver plated and over time tarnish,
had this three time now on Yamaha amps and tuner amps.

Regards Mike
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