Yamaha A-1000 Repair and Info Thread

Did you check the main outputs (TR158 and TR160)?
You can just lift any 2 legs from the board to diode test the transistors.

EDIT - a better question would be which ones are 159 and 160?

I know they are two of the output power transistors, but I am still new to reading schematics, and they are not labeled on the board or in the component layout diagram, so I don't know which is which, or what you mean by center, as there are 4 on each side.

Also , the resistor goes across both driver transistors, so would I not need to check both?
 
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You only need to lift any 2 of the 3 legs to isolate it from the circuit completely (would need at least 2 paths connected for anything to affect it). It's for convenience, you can lift all 3 if you want. Just test between all of them, common mode of failure for outputs is dead-short so you'd know pretty fast.

For more than you ever wanted to know though:
http://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/

2SA (green) = PNP, 2SC (black) = NPN
Easy on those bigger ones with the color coding

Pin order from left to right is E-C-B on every 3-leg BJT transistor in that amp from memory.

Also , the resistor goes across both driver transistors, so would I not need to check both?

Yeah test both, if it were me I'd test the outputs first just because those are the more expensive parts, and kinda the giveaway that stuff will be dead downstream. Fingers crossed for ya. Maybe just lift 2 legs each for all the transistors along that heatsink, then test all the black ones at once and all the green ones at once, will make the testing easier.
 
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Found another burned out resistor, R218. Haven't tested transistors yet, don't know which ones are TR158 and TR160. Once I look at the schematic, find them and look at the symbol I am sure I will be able to tell if the are NPN or PNP, but there are two sets of each on each side, so I will still be guessing.
 
The main output devices are just the two big inner/middle transistors (of the four). The outer two big ones are APS.
Like I said, green = PNP, black = NPN.

outputs2.jpg
 
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It switches in H+ and H- when needed.(M-80/85) In your case its HB+ and HB-....
 
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Making extra loud music...ie making increased power available to the power amplifier output transistors.
 
NPN driver transistor: Short between base & collector = DEAD
PNP driver transistor: Good
NPN HB+ transistor: Good
NPN output transistor: 0.038v between base & collector, base & emitter = BAD
PNP output transistor: base, collector, & emitter all shorted = BAD
PNP HB- transistor: Good

Anyone want a gently used Yamaha A-1000?

Pics with eBay Chinese tester to follow.
 
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NPN driver transistor: Short between base & collector = DEAD
PNP driver transistor: Good
NPN HB+ transistor: Good
NPN output transistor: 0.038v between base & collector, base & emitter = BAD
PNP output transistor: base, collector, & emitter all shorted = BAD
PNP HB- transistor: Good

Anyone want a gently used Yamaha A-1000?

Pics with china tester to follow.

:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(:(

Please refer to the transistors as TR xxx example TR157 please.
 
Any idea what might have gone wrong @avionic ?
From what I can see all boards were resoldered, all cables plugged in / standard, all adjustments set, relay clicked safely on DBT.
Then started dying after relay clicking and idling fine for a few minutes?! Slow bias runaway?

If it helps, I think the TR xxx numbers are:
TR156, TR162 = good
TR158, TR160 = bad
TR140 = bad
TR142 = good
 
Please refer to the transistors as TR xxx example TR157 please.
I would love to tell you but as I told @zaibatsu I don't know, as the numbers don't correspond to anything on the component layout sheet or the exploding diagram...
Very green over here and the schematic is not easy for me to decipher or believe me I would.

It's on the right channel so those are even numbers so,

TR140 = BAD
TR142 = GOOD

Edit: see that Zaibatsu beat me to it.
 
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Update of the disaster with pics as promised. The pictures are in order, left to right, starting with the driver transistors and ending with the PNP HB- (TR162):

IMG_20170622_182846762.jpg IMG_20170622_182948742.jpg IMG_20170622_183032195.jpg IMG_20170622_183112816.jpg IMG_20170622_183141492.jpg IMG_20170622_183254302.jpg
 
@avionic ,


I can't test TR172....I touched the little circuit board that attaches the ribbon cable to the transistor, all three legs literally fell off..:eek:

I would have used the term "snapped off", but that would imply pressure, it just kind of..crumbled..

Here is a pic:

IMG_20170622_230927777.jpg

IMG_20170622_230922919.jpg

EDIT: I tested what was left of the transistor, and it is bad - not that it matters in this case..
 
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Gents,

I got to thinking about it, and I am pretty sure I caused this problem. Of course, that's obvious - I am the only person that has been in this amp.

I mean, I am pretty sure i directly caused this problem.

I was trying to remember what all I had done and I recalled that a week or so ago, I was trying to figure out why TR171 and TR 172 were mounted the way they were. I knew that they were part of the idle current circuit, but I did not understand why they were mounted the way they were, on ribbon cables and all that.

I tried straightening their mounting orientation, making them perpendicular to the heat-sink, as this is the way they are mounted in the Japanese A-1000, which is a slightly different unit. I found that this was okay, but the transistors bent over way too easily when working on the main amp board.

So I decided to orient them parallel with the narrow side of the heat sink, creating more metal to metal contact between the heat-sink and transistors . This worked, but I still had my DMM's hooked up to the bias test points and I noticed that the voltages had lowered once I turned the unit back on. That got me to thinking: maybe these transistors were some kind of temperature regulators, that would lower the bias voltage as they got hotter.

So, I decided to experiment. I sprayed a little freeze spray (upside down duster) and the bias voltage shot up. I put the soldering iron near one, and watched the idle current fall. I figured since a lot of folks troubleshoot transistors like this that it was OK to do and, technically, it was.

I figured from my little experiment that the original orientations were the best, as they provided physical stability for the transistors and let the heat from air convection tell the transistors how hot or cold they were.

For the record, I still don't know exactly what TR171 and TR172 do, but I figure, if they regulate the bias current somehow, then that would backup Zaibatsu's bias runaway theory.

The TLDR/short version of this story is that i played with the TR171 and 172 transistors a few weeks ago and probably fatigued the copper legs on those transistors. Subsequent power cycles caused thermal expansion and contraction on those now weakened legs and cause TR172 to fail.

And while I am one who knows when to admit screwing something up royally, that fact has not made me feel like any less of an idiot.

I am on a budget; this whole ordeal was so I could swap this unit with my main and only system that has been out of order since January. This was a high-stakes operation and I decided to play Mr. Wizard and failed miserably and spectacularly.

This was totally preventable and yet here I am with an amp that now has two fried resistors, two blown output transistors, a blown driver transistor, and a failed whatever kind of transistor TR172 is. God knows what else.

At least @zaibatsu and @avionic will know what happened.
 
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I still don't know exactly what TR171 and TR172 do,

In laymens terms.They thermally track the output transistors to prevent thermal run away. There positioning on the heatsink is some what critical.
 
fictional-locations-mr-wizard-tooter-spell-2.jpg
Old enough to remember this cartoon. Mr Wizard.:D
 
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