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-   -   Yamaha A-760 (http://www.diyaudio.com/forums/solid-state/90149-yamaha-760-a.html)

widman 11th November 2006 11:34 PM

Yamaha A-760
 
I pulled my old A-760 amplifier out of the closet and decided to refurbish it. It ended up in the closet because one channel had a hum and the lights no longer worked.

I opened the chassis and noticed that the big caps had leaked on the main circuit board. I assume that this is the cause of the hum and found replacements at Digikey, but I'm concerned that the electrolytic fluid may have damaged other components on the board. Is this something I should be worried about?

I located the service manual online and figured out that the various lights on the front panel are wired in series. Testing the bulbs for continuity, I found that only the main power bulb was gone and this prevented the other lights from working. I have removed the power bulb, but cannot figure out what I need to replace it. The bulb is ~ 4 mm x lg. with two leads. With the power on I measure 48.8V at the leads. It also has a yellow sheath (condom) that fits snugly on the bulb, providing a baleful amber glow when the power is on. I cannot find a suitable replacement bulb and Im not even sure what I need to be looking for. Is this a neon lamp? Any suggestion would be welcomed.

Thanks.
pete

djk 11th November 2006 11:54 PM

It's a regular lightbulb.

On the A960 the amp will not even turn on if the bulb is open. IIRC it is just a wire lead bulb 12V~14V around 20mA. A hobby shop might have something. Be carefull you don't get too low of a current rating, this would cause over-voltage in the bulb. Too high of a current rating will cause over-voltage in the rest of the series string.

anatech 12th November 2006 12:09 AM

Hi Pete,
Djk is exactly right. I think they were 14V at 40 to 60 mA though. They would prevent the amp from running if blown. A Yamaha favorite thing to do. Buy a spare if you figure out the exact lamp. Call Yamaha first.

Do clean off all the electrolyte. It will cause problems if it's left on there.

-Chris

widman 12th November 2006 01:16 AM

Thanks for the quick replies.

The amp does work without the lights, but only the power light is blown. The other two bulbs still shown continuity.

I emailed Yamaha, but I don't expect to get much information on a 25 year-old amp. I have the main number and will try calling on Monday. Do you guys have any experience in penetrating the corporate shield? Someone at Yamaha can help me, I just need to figure out how to get to the right phone.

I pulled the caps and have cleaned off the electrolytic crust. I also need to clean the pots and blow out the dust. It is actually pretty clean inside, considering its age. Is there anything else I should look at replacing while the amp is in pieces?

Thanks again,
pete

anatech 12th November 2006 01:24 AM

Hi Pete,
Call the service department. If you can get in touch with an older technician, they may help you out. Failing that, an old warranty station that's been servicing these for a long, long time. Still a current warranty depot would be nice.

-Chris

djk 12th November 2006 01:50 AM

I have used lower current bulbs by adding a 12V 1W zener in parallel with the bulb. The zener keeps the lower current bulb from seeing over-voltage, and feeds the right amount of current to the others in the string.

anatech 12th November 2006 02:04 AM

Hi djk,
Neat idea. I haven't tried it.

-Chris

XEAGLEKEEPER 12th November 2006 02:09 AM

Light bulb source
http://www.kenselectronics.com/lists/lites.htm
p/n
RYW-14VF RobynYellowWhiteWire 14V Frosted 80Ma 5.5x14MM 10" leads

anatech 12th November 2006 02:24 AM

Hi XEAGLEKEEPER,
Do you know for sure this is the correct lamp for the A-960? It is part of the protection circuit.

I was pretty sure it was less than 80mA.

Neat site otherwise.

-Chris

widman 12th November 2006 03:17 AM

Quote:

Originally posted by XEAGLEKEEPER
Light bulb source
http://www.kenselectronics.com/lists/lites.htm
p/n
RYW-14VF RobynYellowWhiteWire 14V Frosted 80Ma 5.5x14MM 10" leads

Thanks for the link. The bulb you listed is dimensionally bigger than the bulb I need to replace. Also, my bulb is clear not frosted. I'm sure it could be made to fit, I just want to verify that it has the proper specs.


Quote:

Originally posted by anatech
Hi XEAGLEKEEPER,
Do you know for sure this is the correct lamp for the A-960? It is part of the protection circuit.

I was pretty sure it was less than 80mA.

Neat site otherwise.

-Chris

Just to be clear, my amp is an A-760, although it probably uses the same part as the A-960.

pete


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