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More than just old caps

looxuser

Dec 28, 2015
107
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Dec 28, 2015
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107
Evening all, in my last posting I was asking about sourcing new Capacitors. I did replace them in an old Aiwa amp i'm trying to get going but still no sound output only a feint sound (volume controllable) through the earphone jack. They were pretty shot had blown and made a mess of the circuit board and surrounding area. Fair guess that these would have got the amp working again but sadly not.

So heres what i know from the attached circuit diagram from another aiwa amp, but its near enough the same.

So if you look to the bottom right of the diagram you'll see the top tapoff from the transformer, above that a Relay RY604 and two the left a bridge rectifier and to the left of that the two capacitors ive changed.

So Ive discovered that the relay RY604 is not moving and switching the 50volts to the Amp IC above. On one side of the contacts theres 23 volts positive and negative and on the other side 50 volts again pos & neg. I suspect therefore the amp is not getting power enough to drive speakers but enough to get a squeak from earphones.

So with that in mind I looked at the Relay Drive circuit based on IC 901 HD14001BP. Transistor Q611 to the left (trace the 12.5v) was in a nasty way due to cap leakage so i decided to replace it which seemed to result in 12volts at the relay coil, great but not activating. Im convinced i had not measured and voltage at the coil previously. I then put 12v through the coil with everything powered down and proved the relay works. So thats where ive stopped.

My next step TEST was the desolder the coil leads of the relay to isolate them from the board and to introduce 12v when amp powered up to see if the then throughput of power and from those caps pushes the amp IC to life.

I had thought that c955 100uf/10v in the relay driver circuit may be needed to operated the coil, and as it was so close to the dried out burst caps it may have lifed too. Ive not tested any pins of the IC901 to see whats going on there.

Anyone think of any problems with that TESTd10.jpg i propose or perhaps suggest a testing method for the relay driver circuit please? A walk through of what the driver circuit does and its operation would be most welcome. Many thanks.
 

Arouse1973

Adam
Dec 18, 2013
5,178
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Dec 18, 2013
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5,178
God what a messy circuit diagram. It looks like the main audio output is sampled by the NOR gate IC. When the audio from the main IC is high enough; C909 charges up through D909 this puts a logic high on pins 5 and 6 of IC901 which in turn triggers pins 1 and 2 low which makes pin 3 high and that turns on Q902 and activates the relay.

Thanks
Adam
 

73's de Edd

Aug 21, 2015
3,613
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Aug 21, 2015
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3,613
Model number please . . .you have at least 4 relay sets inolved on that page of circuitry.
 

looxuser

Dec 28, 2015
107
Joined
Dec 28, 2015
Messages
107
hi there 73's de Edd, hope you are doing fine. Yes the model is a MX-D10 although struggled for a circuit diagram and the one i've got looks pretty close.
 

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