Hi guys,
Can somebody help to repair my amplifier?
It is an Yamaha A760II. The power transformator have shorted inside and I do not know what voltage I need for a new transformator.
The amplifier is rated at 100W/8ohm and the filtering capacitors are Elna for Audio 15000u/63V.
The power supply is stabilised on primary side with thirystor and optocupler (Yamaha Xpower I think).
A schematic will be verry good for servicing (I do not know the reasone of shorted tranformator).
I have the schematic for Yamaha A760 but it is very different.
Thank you in advance,
Bogdan
Can somebody help to repair my amplifier?
It is an Yamaha A760II. The power transformator have shorted inside and I do not know what voltage I need for a new transformator.
The amplifier is rated at 100W/8ohm and the filtering capacitors are Elna for Audio 15000u/63V.
The power supply is stabilised on primary side with thirystor and optocupler (Yamaha Xpower I think).
A schematic will be verry good for servicing (I do not know the reasone of shorted tranformator).
I have the schematic for Yamaha A760 but it is very different.
Thank you in advance,
Bogdan
Eservice has parts one and three of it. Don't know what's missing.
Yamaha A-760 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics (part one)
Yamaha A-760 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics (part one)
I have that schematic and is not the right schematic.
The internal layout of the amplifier is diferent.
For example the input of the final amplifier at A760 is clasical - single ended and the input of final amplifier in A760II is diferential simetric,
A760 have 4 capacitors and A760II have 2 bigger capacitors.
You can see some diference between this two models.
Bogdan
The internal layout of the amplifier is diferent.
For example the input of the final amplifier at A760 is clasical - single ended and the input of final amplifier in A760II is diferential simetric,
A760 have 4 capacitors and A760II have 2 bigger capacitors.
You can see some diference between this two models.
Bogdan
Attachments
Are you sure the transformer is shorted and not the rectifiers or the output transistors ??, it would be better to remove the transformer to be sure.
Hi,
With output of transformer disconected from amplifier I measure ~20VAC and ~43VAC on output winding, the input was conected to original triac circuit.
The output is duble so the voltage must to be the same.
With output of transformer disconected from amplifier I measure ~20VAC and ~43VAC on output winding, the input was conected to original triac circuit.
The output is duble so the voltage must to be the same.
Well there you have the answer, the transformer secondary should have +- 43VAC although it seems a little on the high side in view of 63v caps. For 100 Watt stereo you should look at least at 500VA rated one but I know many commercial manufacturers use lesser to reduce costs and for protection.
Before installing new one make sure that other circuitry was not the cause for the failure of the transformer, there might be a shortcircuit somewhere.
Before installing new one make sure that other circuitry was not the cause for the failure of the transformer, there might be a shortcircuit somewhere.
I'd check the transformer with direct mains drive, not through triac. 86V center tapped would give you about +/- 60VDC rails. 88 would be closer with diode drops. I'd suspect the triac circuit before the transformer.
Doc
Doc
Thank you for replay's but,
In a good transformer, if I load one of the secondary to generate a drop in voltage from 45-60AC to aroud 20VAC, on the second secondary output I expect to have a big drop of voltage.
My ideea is that the voltage should be much high that I measured.
Another big problem is that the original power supply is made to work from 100VAC (Japonia). My adapter transformer is at 1/2 result that I power the input with ~115 -120VAC.
The first adapter (for 100VAC out) was broken in the same time with the transformer.
Bogdan
In a good transformer, if I load one of the secondary to generate a drop in voltage from 45-60AC to aroud 20VAC, on the second secondary output I expect to have a big drop of voltage.
My ideea is that the voltage should be much high that I measured.
Another big problem is that the original power supply is made to work from 100VAC (Japonia). My adapter transformer is at 1/2 result that I power the input with ~115 -120VAC.
The first adapter (for 100VAC out) was broken in the same time with the transformer.
Bogdan
THE ...A760 schematic as seen in the picture with 4 capacitors is available .... email me to have it ....
( took a quick look at it but i didn't understand what exactly the control board does .... i presume that something has to do with regulating the input of the trafo or so )
( took a quick look at it but i didn't understand what exactly the control board does .... i presume that something has to do with regulating the input of the trafo or so )
Thank you Sakis but I need schematics for version with 2 big capacitors.
For version with 4 capacitor I already have.
Bogdan
For version with 4 capacitor I already have.
Bogdan
Maybe, without schematic I can put a transformer and to make it to work but I want to repair completely not only to make to work.
I want to have fully functionally, together with main voltage stabilizer.
Sakis thank you for interest and I wait for news.
Bogdan
I want to have fully functionally, together with main voltage stabilizer.
Sakis thank you for interest and I wait for news.
Bogdan
Guys I have a schematic for the A760II, let me know how to get it to you. I am also looking for help understanding it so I can replace the bulbs in my burnt out A760II here...maybe we can help each other?!
Hi Agvo,
I have now the schematic. Thank you!
All bulbs are powered from a current source. You can use a bulb that work at the same current and fit in place of old bulbs.
I hope to have time, in some days, to change the bulbs with LED's because the current source use a lot of power, and to change some capacitors from signal path.
I have now the schematic. Thank you!
All bulbs are powered from a current source. You can use a bulb that work at the same current and fit in place of old bulbs.
I hope to have time, in some days, to change the bulbs with LED's because the current source use a lot of power, and to change some capacitors from signal path.
Please replace the RIFA cap at Power Supply!
Hi,
It's STRONGLY suggested by Yamaha to replace the X-rated 0,47uF 250V RFI capacitor at power supply section with a X2-rated 0,47uF 275V.
This is valid for BOTH versions, the A-760 and the A-760II.
Restoration of a Yamaha A-760 vintage integrated amplifier
Hi,
It's STRONGLY suggested by Yamaha to replace the X-rated 0,47uF 250V RFI capacitor at power supply section with a X2-rated 0,47uF 275V.
This is valid for BOTH versions, the A-760 and the A-760II.
Restoration of a Yamaha A-760 vintage integrated amplifier
Hi Karl,
I do not use anymore the X-Power module, so these capacitors are not present anymore.
Anyhow the amplifier it is Yamaha A-6a not A760II. On internet I find a information that these two models are the same, A-6a made for Japonia and A760II made for Europa, but I compare the specification of these two models and are diferent, the Europa model has less power (-~20W)
I do not use anymore the X-Power module, so these capacitors are not present anymore.
Anyhow the amplifier it is Yamaha A-6a not A760II. On internet I find a information that these two models are the same, A-6a made for Japonia and A760II made for Europa, but I compare the specification of these two models and are diferent, the Europa model has less power (-~20W)
Hi,
I change only the transformer with one custom made, 2 x 43-44Vac, ~56Vdc on capacitors without signal, 350W toroidal.
According to people from here, for 2 x 100W/8Ω I will need over 500W transformer BUT after 7-8h of almost maximal power, the transformer remains cold, so no need more powerful transformer, maybe even 300W it is enough.
For preamps I used another (small <10W) transformer and standard regulators (7815 & 7915) and I modified the schematic to power low signal amplifier from these regulators.
I ordered polyester capacitors to change all (polarized) capacitors from signal path but not arrive yet.
I forgot to mention, my amplifier it is Japanese model, so the more powerful model.
I change only the transformer with one custom made, 2 x 43-44Vac, ~56Vdc on capacitors without signal, 350W toroidal.
According to people from here, for 2 x 100W/8Ω I will need over 500W transformer BUT after 7-8h of almost maximal power, the transformer remains cold, so no need more powerful transformer, maybe even 300W it is enough.
For preamps I used another (small <10W) transformer and standard regulators (7815 & 7915) and I modified the schematic to power low signal amplifier from these regulators.
I ordered polyester capacitors to change all (polarized) capacitors from signal path but not arrive yet.
I forgot to mention, my amplifier it is Japanese model, so the more powerful model.
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Very interesting. Maybe there's an A-760II on the way to me as well.
Would be interesting if you, when putting new components again in it, taking a few pictures from internals of your mods . 🙂
Thanks
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On what you are interested?
It will be difficult to see the modification from photos. If I will know exact what you are interested, I can explain exactly what to change.
By the way, do you know that these models work in class A variable and contain a special circuit named ZDR, circuit that it is supposed to reduce the distortion generated by output power transistors?!
It will be difficult to see the modification from photos. If I will know exact what you are interested, I can explain exactly what to change.
By the way, do you know that these models work in class A variable and contain a special circuit named ZDR, circuit that it is supposed to reduce the distortion generated by output power transistors?!
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