A-960 II trouble

Got a rare black A-960 II today. The amp looks like new (I will post pics later on). The previous owner told me, that "there is a no sound coming out". Definitely true. Apparently somebody has already tried to repair it without success. The power transistors (Sanken A1169/C2773) on the right channel were desoldered. Both are shorted, so are the drivers (A968/C2238), too. I did not look further by now.
My major problem is the Main Direct switch. It does not work any more, neither electrical nor mechanical. The rivets were seriously bent. I could halfway restore their original shape. But, the switch does not hold the position which activates "Main Direct". The plastic rails which guides the metal axle is worn out. I would like to replace the switch. Is there any drop in replacment available? It has a 2x9 pin arrangement (pls see attached pic).
BTW, I would appreciate any hints which parts to check before I drop in the new transistors.

Yep. The main/direct switch is a common problem. I found a replacement that works.

Here's the link:

http://www.audiokarma.org/forums/showthread.php?t=384712

Looks like it's out of stock right now at Digi-Key, but it doesn't say it's discontinued or anything.

--Tim

timothya said:

Yep. The main/direct switch is a common problem. I found a replacement that works.

Here's the link:

http://www.audiokarma.org/forums/showthread.php?t=384712

Looks like it's out of stock right now at Digi-Key, but it doesn't say it's discontinued or anything.

--Tim

Click to expand...

Mouser has them instock
http://www.mouser.com/ProductDetail...02pXKJamOSjSHgtF2D/1NquxT7HhQ8jnDzrNt7blAAg==

Thanks, I have already ordered the switch.
I urgently need the service manual. I found some burnt resistors and a lot of shorted transistors and have the schematics only.

E-mail Norman . He supplys high quality pdf scans.
http://www.analogalley.com/m_yamaha.htm

importance of hfe value?

I downloaded the SM from Norman. It is indeed a very good quality copy.
May I ask the experts another naive question: The 2SA1494/2SC3858 Sanken output devices I got from Digikey (I had ordered "Y" but received "P") have a much lower HFE than the original parts. Is this a problem?

Dr. Ear said:

I downloaded the SM from Norman. It is indeed a very good quality copy.
May I ask the experts another naive question: The 2SA1494/2SC3858 Sanken output devices I got from Digikey (I had ordered "Y" but received "P") have a much lower HFE than the original parts. Is this a problem?

Click to expand...

Probably not for and output. I didn't know Digikey stocked them. I've always ordered them through BDEnt.

dr. Ear said:

i downloaded the sm from norman. It is indeed a very good quality copy.
May i ask the experts another naive question: The 2sa1494/2sc3858 sanken output devices i got from digikey (i had ordered "y" but received "p") have a much lower hfe than the original parts. Is this a problem?

Click to expand...

y ( 50 - 100 )
p ( 70 - 140 )
g ( 90 - 180 )

LED-Upgrade?

Amplifier is working again. Replaced 6 transistors and 4 resistors. DC offset (which you cannot adjust in this model) is ±2mV or below.
The illumination drives me crazy. I tried to replace the bulbs by LED's as I did with my C-4/M-4 combo. But, in the A-960ii this does not work. When I press the main direct button, the power button light dims. Muting light does not work at all. Polarity is correct. Has anybody successfully managed to install LED's in an A-960ii? Does the service bulletin mod. also apply to this model?

Dr. Ear said:

When I press the main direct button, the power button light dims.

Click to expand...

Sounds like a power supply regulation issue ...

Hi Dr. Ear,

Th A960II is in the service bulletin AFAIK it is mostly for the 220v versions.
http://www.whathifi.com/News/Yamaha-issues-safety-recall-on-amps-30-years-on/

Great work on fixing the A960II :thmbsp:

No, it's not. I found out that the bulbs are connected in a serial array. In position "off" they are bypassed by a resistor. If you use other bulbs than specified (or LED's) the illumination does not work properly.

Keessie said:

Hi Dr. Ear,

Th A960II is in the service bulletin AFAIK it is mostly for the 220v versions.
http://www.whathifi.com/News/Yamaha-issues-safety-recall-on-amps-30-years-on/

Great work on fixing the A960II :thmbsp:

Click to expand...

Thank you! Of course, I have replaced the X- and Y-caps in the PS.

Finally I got the lights working - I put the original bulbs back. Sorry, no LED's this time. I reassembled it, double checked everything, connected my iPod and my old Yamaha HP2 headphones and switched it on. I was expecting it: There was no sound:tears:
Found the solution soon: The Bowden cable to the input selector switch was not connected...
I have now listened to a few records and must confess this amp sounds fantastic. Bass tunes make you tapping your feet. I can't wait to hook it on my NS-2000 tomorrow.
The construction is a bit weird. The illumination is a nightmare. The heat sink of the left channel has to dissipate the additional heat of the voltage regulator, too. With absolutely identical idle current and the absence of oscillation the temperature is almost 10°C higher than it is in the right channel (40° vs 32°). Maybe this thermal asymmetry was the reason for the failure (?). The new Sanken output devices have a power dissipation of 200W which is better than the 150W of the original parts.
Will post pics tomorrow.

Pictures

The A-960ii is now playing together with my NS-2000 and the Thorens TD-2001 with an AT-150MLX cart. I would describe the sound of this amp as very colorful, full bodied, with great bass and a good soundstage. There is plenty of power. Compared to this, my C-4/M-4 combo is more on the lean side. I posted a few pics. There were lots of problems caused by the notorious Sony glue and many broken solder joints. The job took me almost 8 hours.