• Please note that there are a few updates and clarifications made in the Audiokarma Rules, mostly relating to advertising and the addition of the new "Paying it Forward" & "Giving back" forums in the AudioKarma Audio Marketplace section.

Yamaha A-1000 Repair and Info Thread

I like that @avionic !
Yeah, this Mr. Wizard was a little before my time, but thanks to the internet, I can now say I feel like tooter turtle:

Start:

hqdefault.jpg

Finish:

Wreck.JPG

Well, I am feeling a little bit better about this mess than I did yesterday; at least I was kinda close to figuring out what those transistors did, but prevent thermal runaway something I didn't think of, I thought of it more a like a thermal regulator, but that is probably because of my computer background interfering with my thinking of how amplifiers work. Do most amps have this or was this a Yamaha thing?
 
I do have some questions moving forward, if there is a way forward through this mess:

Is there anything else I need to check, or is this issue contained within what is already damaged?

Is there even a point in trying to repair it? I don't even think you can get the big power output transistors anymore.

I don't know much about how the "complimentary pairs" thing works but I would think it would be important?

And if I find them, do I need to replace the other channel's output and driver transistors to balance the system out?

What about the driver transistors, do they need to be matching as well?
 
Last edited:
tmsears said:
Is there anything else I need to check, or is this issue contained within what is already damaged?
Click to expand...
If I were doing the repair. Every transistor and diode in the effected channel would be removed and tested out of circuit. Most every bad resistor would be visually apparent. But some are not. Thats why it helps alot if you understand DC circuits and current flow.Understanding how transistors and other components are suppose to work and work together is key.
 
On these yamaha amps I print out a schematic of the circuit in question. Then as I discover bad or burnt parts . I will identify them on the schematic with a highliter.. Like the example of a B-6 below.
index.php


This way I can get a better idea of what needs to be checked and verified good or bad.
 
I probably should have mentioned something about those bias transistors, they are mounted in a really flimsy way on these amps. I unscrewed mine to stop myself bumping them while working, but other Yamaha amps like the M-series use screw-hole packages (like TO-126) with thicker legs and have a much more durable mounting setup.

I didn't want to suggest something I hadn't tested, but since we're here now...
I wanted to fix the problem permanently, so I poked around until I found a close match for specs (to the 2SD-400) in a TO-126 package, and came up with the BD-135.
I'll post some pics of what I did later if you're interested. I have mounted everything, but am not able to test yet.

If you want to fix the amp you will definitely be able to.
@avionic helped me fix mine, I can share what I learned.

You can use these for the main output devices:
https://www.digikey.com.au/product-detail/en/sanken/2SA1494/2SA1494-ND/3929367
https://www.digikey.com.au/product-detail/en/sanken/2SC3858/2SC3858-ND/3661814

That will be the biggest single-part expense (i.e. not the end of the world) and everything else is cheap, the only real cost is time.

With the help of the DBT and a little creativity with meter measurements (with the amp unpowered but components still in circuit) I've managed to fix a few now without removing many parts. Obviously in-circuit measurements are not always accurate, but having the good channel to compare with helps give clues about problem parts.

The first thing I'd do is remove the 2 main output transistors on both channels from circuit (circled ones in my pic). You can just desolder and move legs off the board. Then solder a 470Ω 2W resistor across their B-E pads on the board. At this point the amp will live on the DBT + 100W until you get a relay click again. New outputs won't go in until that happens.

You'll need to find some subs for the driver transistors too, the subs I used are now discontinued (Toshiba 2SA1837 and 2SC4793).
Edit - bdent still has these, it wouldn't be crazy to buy a few, as they're no longer produced:
http://www.bdent.com/2sa1837-toshiba-audio-power-transistor.html
http://www.bdent.com/2sc4793-toshiba-audio-power-transistor.html
They also stock the aforementioned outputs:
http://www.bdent.com/2sa1494-sanken-audio-power-transistor.html
http://www.bdent.com/2sc3858-sanken-audio-power-transistor.html
 
Last edited:
avionic said:
On these yamaha amps I print out a schematic of the circuit in question. Then as I discover bad or burnt parts . I will identify them on the schematic with a highliter.. Like the example of a B-6 below.
index.php


This way I can get a better idea of what needs to be checked and verified good or bad.
Click to expand...
Usually when Yamaha's go south. They take a lot of parts with them.
 
Ok. Before I mention anything else, I want to acknowledge @zaibatsu and @avionic for all the help they have given; Zaibatsu for the daily help and layman's terminology, and Avionic for his expertise with Yamahas and years of experience. Both of you are outstanding gentlemen and I appreciate the help a lot. You two are real assets to AK.

That being said, while I do want to fix this amp, I don't even know if it is possible given that I can't seem to find the Sanken 2SA1494 and 2SC3858 for sale in a complimentary / matched pair. I am new on this stuff so I could be wrong, but in order to be matched I thought they had to be bought that way? The ones on digi-key don't look to be matched, and they are out of the 2SA1494.

Another concern I have is finding the driver transistor pair. I don't know how to substitute those an the internet has not been very helpful from what I have seen so far.



I have $70 left that I can spend and I have to make it count. I don't know if it is wiser to continue on or to try to recap and clean the M4 and C6..but if I mess those two up then may really be up a creek if I have to sell them.
 
You don't need to match outputs in this case.
The only time you would need to match output devices is when there are paralleled pairs, then you would match the NPNs with the NPNs and PNPs with PNPs. The A-1000 uses a single (big) output pair, so you will be fine to literally just buy a pair. Bdent has both in stock from what I saw. Bdent also has the driver subs in stock. See my edited post.

If it were me, I would get the relay clicking with NO outputs installed, then get it running with your subs installed. Then, as an optional finishing touch (once everything is fixed), I'd swap the two APS transistors with the outputs on the previously-bad channel so that you have factory outputs both sides, and relegate your subs to APS duty. The cool thing about these APS amps is they kinda carry a spare set of genuine outputs for themselves.

If you can figure out exactly what (else) you need with a little testing, I can offer to send a care envelope with the parts you need. I think I have most parts spare except the outputs. That way you could maybe try and get a relay click before spending anything. Just an idea.
 
zaibatsu said:
You don't need to match outputs in this case.
The only time you would need to match output devices is when there are paralleled pairs, then you would match the NPNs with the NPNs and PNPs with PNPs. The A-1000 uses a single (big) output pair, so you will be fine to literally just buy a pair. Bdent has both in stock from what I saw. Bdent also has the driver subs in stock. See my edited post.

If it were me, I would get the relay clicking with NO outputs installed, then get it running with your subs installed. Then, as an optional finishing touch (once everything is fixed), I'd swap the two APS transistors with the outputs on the previously-bad channel so that you have factory outputs both sides, and relegate your subs to APS duty. The cool thing about these APS amps is they kinda carry a spare set of genuine outputs for themselves.

If you can figure out exactly what (else) you need with a little testing, I can offer to send a care envelope with the parts you need. I think I have most parts spare except the outputs. That way you could maybe try and get a relay click before spending anything. Just an idea.
Click to expand...

Ah, I see, I thought the PNP and NPN had to match each other in some sort of value, shows what I know! I appreciate he offer, I may just take you up on it. I have that little tester so it can't hurt to at least try to do a damage assessment.

Edit - I figured out how a got confused - I had once read about matching differential pairs, like Zaibatsu refers to below.

Edit - removed my late night gibberish
 
Last edited:
tmsears said:
Ah, I see, I thought the PNP and NPN had to match each other in some sort of value, shows what I know! I appreciate he offer, I may just take you up on it. I have that little tester so it can't hurt to at least try to do a damage assessment.

@avionic sent me a thread to read up on about the DC offset on my M4, so maybe I can get it going well enough again to have it substitute for itself! That was a little too funny so I am off to bed to think about all the options.
Click to expand...
Just from your description The M-4 will most likely just be and adjustment.
 
avionic said:
Just from your description The M-4 will most likely just be and adjustment.
Click to expand...

That's good to know. :) I will read through your guide when I have a chance, I may have a few questions -The M4 is my baby after all-

The original thought was that I would use the A-1000 while I took my time and re-capped the M4, since it is nearly 40. Then the A-1000 broke 5 minutes into using it, and it became the recap project, and well, we all know the rest.
 
Last edited:
Ok, on @zaibatsu 's suggestion I checked the following transistors, and here is the results:


TR120 = Good
TR128 = Bad
TR130 = Bad
TR132= Good
TR136= Good
TR138= Good
 
Typo on my part, only needed to check TR128, TR130, TR136, TR138.
Anyway sounds like the common failure mode to me, looks good.

Check R216 as well, should be 33Ω, may have failed.

Remove and check R264, R266, R268, the large white cement moulded resistors. All 0.22Ω. Likely still good but need to check.

If you have some spare time it's probably worth checking all those standing flameproof resistors on the bad channel, you can just test them in-circuit for convenience, from memory most/all of them can be checked in-circuit. If anything looks suspicious you can first compare to the in-circuit measurement of the matching flameproof (if there is one) in the good channel, and if still suspicious you can pull and test the bad one properly.
 
Last edited:
I have not have a lot of time this week to work on the amp , but I am going through the flameproof resistors and there are more burnt out than originally thought. When I finish testing them I will go through my notes on what is what and report back.
 
Well gents (@zaibatsu ,@avionic ), After a week of severe earaches and headaches, I finally managed to test all the standing flameproof resistors, the ceramic power resistors, and the transistors that were suggested.

Here is the list of everything that tested bad:
TR128
TR130
TR140
TR158
TR160
TR172

R216
R218
R264*
R266
R268*

* These tested iffy. They tested at 0.16 ohms instead of 0.22 -but- so did the resistors on the other channel, which I removed and tested to verify.

So, I think I can handle putting together a shopping list for the resistors, but I am going to need some help on the transistors, and their substitutes.

I am trying to keep the shipping costs down, so I am going to try to get everything from B+D and mouser, if at all possible.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom