Yamaha A-760 with "X Power supply" - Help!

[Gigapod]

Hi,
My first post, asking for help from some of the amp gurus here.

I bought a "burned, sold as-is" Yamaha 1980's amplifier on eBay. This is a MOTL (middle-of-the-line) Natural Sound A760 conservatively-rated 2x80W RMS model.

The "burned" part was quite obvious upon removing the cover. I have taken a few pictures, two of which are shown below:


And I have also here the relevant circuit from the schematics:


I removed the remains of the capacitor, cleaned up the spilled oil, changed a burned lamp for a white LED + resistor, and after a few tests, fired it up, and it's working!

However, I would like some help concerning the following:
1) I read this amplifier uses a variable power supply, a concept that Yamaha seems to have copied from Carver (?). Is the blown capacitor part of the variable supply circuit and am I risking something by using the amplifier without it?
2) Can I replace the capacitor by an equivalent type and which one would you recommend? I don't want something that will blow again!
3) Anything special I should do/check about this amp, or just sit back and enjoy the sound ? BTW I found a copy of the service manual on the web.

Thanks for your help and reading this far.

[PMik]

There is no harm running the amp wo the cap., other than it can be more sencible to noise.

It is rated in 250VAC which is eqv. to 400VDC, so you can replace it with a 0.47µF/400V- capacitor from WIMA/RIFA/ERO or other known relieble brands

[AKN]

Hi Gigapod,

That cap will shunt HF nise on powerline in to amp and out from amplifier. Make shure you replace with a X rated cap with the same voltage and capacitanse.
X rated caps are allowed to be connected across power line, Y rated caps from line to ground.
More on this here:
http://72.14.253.104/search?q=cache:...s&ct=clnk&cd=2

[PMik]

And we here in Europe are used to very unrelieble powersupply ?

X rating is pure overkill and in reality only of interst to prevent a vendo in a worst case situation,
beeing dragged into a civil law suit.
So no need to replace with a X rated cap ..., if you have to be more curtiuos replace for a 0.47µF/630V-

[AKN]

Hi PMik,

A 0.47uF X cap is below $2 and are very common as they are used almost everywhere, why not stick to original specs?

[PMik]

Lazyness i guess ..., for instance a RIFA 0.47µF/400V- will easy cope with an AC peak voltage above 350 Volts, that is in my pov. more than sufficient for the purpose needed in this occation.

[AKN]

Hi PMik,

There is another more important view of this, especially when replacing components on mains.

If we recommend any other here to replace a component and say that any compomponent will be fine as the basic properties are ok and neglecting classifications etc, we are indirect/direct reponsible for what happens if something goes wrong. It may not go wrong at all if the right component is chosen but suppose someone goes out and by a very poor cap and something blows. If You and I does something out of "lazyness" for our own sake that is one thing, but to teach that to others is wrong in my point of view.

[PMik]

You must be very unsecure regarding what safety limits MP capacitors are produced with, this kind of malfunction shown in this tread i have personal only come by mayby a dusin times or a few more over an periode of 30 years with HiFi ..., so get real! curse the worst case scenario you expect is infact a very rare one

[AKN]

PMik,

I am real thank you.
I have about the same years in business and have apparently
drawn a different conclusion, others may conclude what's right.
Let us now have a good start into Cristmas day.

Cheers!

[AudioFreak]

Guys,

What you do with your own equipment is one thing but when handing out advice, please keep it legal. X rated caps for across mains and Y rated caps for mains to earth. Killing yourself is one thing ... killing someone else thru poor advice is another. Failures may be rare but when dealing with something that can and does kill people don't take risks with someone else's life.