CurtPalme.com Home Theater Forum

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

I came home today from work and my Tenant was in his garage and asked me if I wanted his A1 integrated. He said the tech said its outputting DC on the Speakers outs. I said sure and brought it inside. I looked it up and seems to be a well regarded Amp.

So Where do I start diagnosing why its outputting DC? Shorted Output Transistors?

'I'm looking for the schematics now....

Athanasios

**AnalogRocks** · Posted: Sat Mar 17, 2012 9:27 pm Post subject:

Mac in 5....4.....3......2.....

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

**Curt Palme** · Posted: Sun Mar 18, 2012 5:02 am Post subject:

Yeah, real nice... until you have to work on it. Smile

YEs, you're right, this is a pretty highly regarded audiofool amp. Problem is, as you can see when taking the lid off, it's damn complicated. Yamaha overall is known to blow everything up in the signal chain when one channel blows.

NOw, I find it hard to believe that there's a bunch of DC output on the speaker lines, as these amps have protection in them that should kick the relay out when there is DC on the line. (BTW, where the hell do you find a tenant that knows about DC on the speaker line????)

NOw, if you find equal amounts of DC on each amp output, hopefully you got lucky and have an issue in the power supply somewhere, and the amps are still OK.

I only ever have seen one of these, and the amp channel was so fried, and I believe (but could be wrong) that the output uses obsolete MOSFETS, so I sold it as is on eBay for stupid amounts of money. That of course was before I knew Mac, who could cross any part that I've thrown at him. Smile

HK-Steve · Posted: Sun Mar 18, 2012 6:48 am Post subject:

I have a schematic, can send it to you by email,

PM me your address.

Cheers
Steve

HK-Steve · Posted: Sun Mar 18, 2012 6:53 am Post subject:

and I also have the service manual, it is 24gb, not sure my email provider will let me send it, but will try.
schematics are 11gb.

Cheers

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Just stick your probes in the speaker terminals and see if the is any DC reading. Should be none.

erikjohn · Joined: 08 Mar 2006 Posts: 636 Location: Florida

Is it the A-1 or the DSP A-1? If it is the latter it will have and internal diagnostics routine that you can initialize, not sure about the A-1, it may have one also.

EJ

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Steve if your on Skype later we can do the file transfer thing.

Mac And Curt, I know that this has a protection circuit. My tenant took it to a local Shop who told them it had DC on the outputs. I have not even powered it up yet. But there is a couple suspect areas where there looks like some corrosion or goop came out of got spilled in. not sure I doubt it was spilled in there as my tenant is meticulous. He told me he had the relay for the speakers changed about 10 years ago.
The output transistors from what I can see look nice and clean. I'd have to power her up and see what she does, that is listen for relays, transformer hum etc.

Still at work so it will be a while before I can begin checking things out.

Oh also the door is missing, where can I get one?

Athanasios

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Ok Powered her up and I hear the relay click . If i tun the speaker button off, power it off and turn it on no click as no speaker is selected, i hear a click when I now press the speaker button and reading the Outputs its .055 DC with volume down and goes up and fluctuates from .230 to .432. Both channels are similar. Wouldn't there be 0 DC if the protection circuit goes on? I don't have any crap speakers to hook up and test.

Athanasios

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Ok New problem cause I am in idiot!! I wanted to measure the one resistor that looks like its all corroded etc. It was unplugged but I should no better that those huge caps hold lots of juice!! I had a small spark and new i f*ck*** something up. Went to power on and smoke from the left turquoise resistor in this pic.

Damn it!!! I should have known better!!!

Athanasios

Jeremy112 · Joined: 28 Sep 2006 Posts: 2649 Location: Fond du Lac, WI

We were given a yamaha C-50 and yamaha M-50 for free because the amp was blown up. Once we opened it, OUCH you could see how bad it was fried. After doing some checking, quite a bit was blown up in the amp, unfortunately it was not worth buying the new parts for since they would have cost about what the unit sells for working.

Your Yamaha A-1 looks rather similar in design to the C-50 preamp. You have yourself a nice unit if you don't kill anymore parts in it Razz

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

gee thanks Jeremy! Wink

I think its just one of those transistors. and the 330Ohm resistor.

I'll take it from the kitchen to the shop and take that board out and check the part. Oh boy.

I'll Use a 1K 2 watt resistor and short the large filter caps to ground this time. And looking at it from underneath this could have easily been done, just stick the resistor in there and touch the chassis! doh!!!

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Ok here is the bad transistor, surprisingly the 330ohm R is still reading 330 Ohm.

I can't find it with just the numbers on it. What make is it? Symbol is not familiar.

Nashou

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

That would be a 2SA913 which is pretty much non existence. Here is a replacement: http://www.mouser.com/ProductDetail/NTE/NTE398/?qs=JV7lzlMm3yKF%2fZcCC1fPeQ%3d%3d

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Is it a regular A-1 or the DSP A1? I can get either schematic. I'm off for the night so I'll check back tomorrow.

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Just the A-1.

Thanks Mac

Nashou

**AnalogRocks** · Posted: Mon Mar 19, 2012 12:39 am Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Schematics in your email....