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Topic: Help needed repairing an Yamaha A760 Amp (Read 7291 times) previous topic - next topic
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Help needed repairing an Yamaha A760 Amp

Hello everyone, i just signed up here because i need help.. i like to apologize in advance that i wont be able to contribute in the future,
because i dont know much about hifi equipment at all, besides that i appreciate good sound.

I've got a quite old setup consisting of just a record player and an amp and speakers.
in case it interrests you, an Thorens TD 160 MkII with an akg p8e pickup, and an Yamaha A760, and quite average Magnat 8Ohm 100W 3way speakers.

Today, my amp gave me the "blue smoke"..
i've blown this cap http://i.imgur.com/PW1qGAl.jpg  and already ordered an "MKP-Funkentstör-Kondensator radial bedrahtet 470 nF 275 V 20 % 22.5 mm (L x B x H) 26.5 x 8,5 x 17 Kemet R46KN347000M1" as replacement, which should work well enough.. (according to that guy over here: http://gigapod.free.fr/Yamaha_A760.html )

but i noticed a corroded diode too.. http://i.imgur.com/yq55iY9.jpg
i'm completely lost. im quite sure its a zener.. looking at all resources i could finde online: http://i.imgur.com/K29BOnC.jpg i'm quite confident it's that one. but that does not help me much either..
i can't even find it on here http://i.imgur.com/nOIfAfq.jpg


many thanks in advance to anyone knowledgeable that i willing to spare a bit of his/her time to bring music back into my life..

edit: im currently using an L&G L-2600 as a temporary replacement, but this baby is so sensible to interference and em noise.. i have to crank it up to 8, to get nice background volume.. maybe it was not designed to power a MM pickup without a preamp.. or it is broken as well.. it hums and crackles even when the needle is in the air..

Help needed repairing an Yamaha A760 Amp

Reply #1 –
Quote from: valravn on
Hello everyone, i just signed up here because i need help.. i like to apologize in advance that i wont be able to contribute in the future,
because i dont know much about hifi equipment at all, besides that i appreciate good sound.

I've got a quite old setup consisting of just a record player and an amp and speakers.
in case it interrests you, an Thorens TD 160 MkII with an akg p8e pickup, and an Yamaha A760, and quite average Magnat 8Ohm 100W 3way speakers.

Today, my amp gave me the "blue smoke"..
i've blown this cap http://i.imgur.com/PW1qGAl.jpg  and already ordered an "MKP-Funkentstör-Kondensator radial bedrahtet 470 nF 275 V 20 % 22.5 mm (L x B x H) 26.5 x 8,5 x 17 Kemet R46KN347000M1" as replacement, which should work well enough.. (according to that guy over here: http://gigapod.free.fr/Yamaha_A760.html )

but i noticed a corroded diode too.. http://i.imgur.com/yq55iY9.jpg
i'm completely lost. im quite sure its a zener.. looking at all resources i could finde online: http://i.imgur.com/K29BOnC.jpg i'm quite confident it's that one. but that does not help me much either..
i can't even find it on here http://i.imgur.com/nOIfAfq.jpg


many thanks in advance to anyone knowledgeable that i willing to spare a bit of his/her time to bring music back into my life..

edit: im currently using an L&G L-2600 as a temporary replacement, but this baby is so sensible to interference and em noise.. i have to crank it up to 8, to get nice background volume.. maybe it was not designed to power a MM pickup without a preamp.. or it is broken as well.. it hums and crackles even when the needle is in the air..


When an amp is old enough to start losing film capacitors and diodes, it has probably only just started to cause you troubles.  Fix these problems and wait a few weeks or months for your next excitement!

The zener diodes in power amps like this are probably part of some kind of a protective circuit.  It is obviously a low powered part - a watt or less.

The question for the day is what its zener voltage is. There are several so one approach would be to pull out one of the others and measure its zener voltage. Then find a general replacement part with the right zener voltage and an equal or larger wattage. 

Here is an online article about how to do that:

http://www.learningaboutelectronics.com/Ar...t-a-zener-diode

The test with the 9 volt battery will only work for zener diodes with zener voltages up to 8-9 volts.  This one may have a higher zener voltage than this. 

You might have to use several batteries in series to get a representative reading.