Yamaha A-760

[widman]

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 Ø x ½ “ 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 I’m not even sure what I need to be looking for. Is this a neon lamp? Any suggestion would be welcomed.

Thanks.
pete

 

[djk]

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]

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]

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]

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]

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]

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

-Chris

 

[XEAGLEKEEPER]

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

 

[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

 

[widman]

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.

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

 

[XEAGLEKEEPER]

I have used this bulb in several Yamaha units. A T-1 tuner required a 14.5vdc @ 80ma. As far as the A-960,A-760 not 100% sure if you have doubts, that same website has others to choose from . It just worked fine for me. Yamaha (japan) uses weird oddball bulbs that are no longer available so you got to do what ya got to do,give it a go. As for the A-760 what have you got to lose besides $1.20 it will either work,be to dim or burn out quickly.

 

[widman]

That is more or less what I had in mind. I'll get a handful of sizes and see what works best.

pete

 

[widman]

I heard back from Yamaha and the A-760 uses the same bulb (14.5V, 80 mA). Thanks for the help.

pete

 

[XEAGLEKEEPER]

I figured that there was a good chance it was. That part # I sent you will fit inside that rubber boot. Happy thanksgiving day.

Later Dave

 

[anatech]

Hi widman,
Cool!
I didn't think they were that high in current. I am glad you checked with Yamaha. Never guess when a lamp is part of a circuit and not just an indicator.

-Chris

 

[widman]

I was surprised to hear back from them on such an old piece of equipment. They even suggested checking with the parts department to see if the bulb was in stock.

As it stands, I'm waiting on my bulbs to arrive from Ken's Electronics and the caps to arrive from Digikey.

pete

 

[widman]

I received my parts and replaced the caps & power bulb. The lights shine and the amp sings again.

I do get noise when moving a few of the controls. Specifically the treble, loudness and balance control are very scratchy. Also, the Main Direct button (bypasses the control section) is very noisy when pressed. I guess I need to spray down these controls with contact cleaner. Is there a recommended brand and do I have to remove the controls before using it?

pete

 

[XEAGLEKEEPER]

Flush the controls liberally with electrosol or similar then get some Deox-it made by CAIG this stuff is pretty pricey but a little goes along way. Radioshack sells some very small aerosols for 14.95 . The deox-it is IMHO the absolute best. Go to CAIG.com and check it out! I think you can purchase it straight from them.As far as removing controls maybe, maybe not depends if you can easily access the small openings on the controls or not.

Later Dave

 

[anatech]

Hi Dave,
Sorry, I'm going to disagree with you again on this ........

Flush the controls liberally with electrosol or similar

No! You do not want to wash out the protective lubricants (grease) on the carbon track! The noisy part is the wiper and slip ring. A little applied on the slip ring will cure the noise. I use a dropper with a metal tube (small like a large bore needle). If you take the control apart and clean the oxides off the slip ring and reassemble the control, the noise will be gone for a long time. Normally this is not possible.

-Chris

 

[XEAGLEKEEPER]

DeoxIT® contact cleaner is a fast-acting deoxidizing solution that cleans, protects, lubricates and improves conductivity on all metal connectors and contacts. Use as a general treatment for connectors, contacts and other metal surfaces, and on non-critical metal surfaces with severe oxidation and corrosion. If the metal surface is discolored, it is severe. DeoxIT® dissolves the contamination and protects the surface. For reference, DeoxIT® has approximately 20% cleaning action.