Yamaha HT-R4065 won't start

[tibimakai]

Re: Yamaha HT-R4065 won't start

I will check it out in the morning.

[tibimakai]

Re: Yamaha HT-R4065 won't start

It was open.
So this caused the blow up, right?
I should receive the ordered components on Friday.

[rievax_60]

Re: Yamaha HT-R4065 won't start

It was open.
So this caused the blow up, right?
I should receive the ordered components on Friday.

Yes, that is a good reason for the output transistors and drivers failing.
Is the bias transistor ok?

[tibimakai]

Re: Yamaha HT-R4065 won't start

Yes it's fine. I have ordered another one just in case.
I would like to ask you about this transistor, why they are installed under the main heatsink with thermal paste?

[rievax_60]

Re: Yamaha HT-R4065 won't start

Yes it's fine. I have ordered another one just in case.
I would like to ask you about this transistor, why they are installed under the main heatsink with thermal paste?

Its for thermal feedback.
As bipolar transistors increase in temperature, they will conduct more Collector to Emitter current for a given applied Base to Emitter bias voltage, Vbe.
This would cause the idle current though the output transistors to increase causing more temperature rise and higher idle current again. This process will snowball until the transistors fail.
The bias transistor or Vbe multiplier as its also called, controls the total bias voltage that is shared out to the Base to Emitter junctions of all four transistors in the output stage. Notice that all of the Base/Emitter junctions are kind of all in series with each other.
As the bias transistor senses higher heatsink temperature, the resistor divider strung from its Collector to Base to Emitter causes its Collector to Emitter voltage to decrease because now the the bias transistor itself needs less applied Vbe to be turned on.
Also notice that the Collector and Emitter of the bias transistor connect to the Bases of the output's driver transistors.
The actual bias current is supplied by the preceding signal voltage amplifier stage.

[rievax_60]

Re: Yamaha HT-R4065 won't start

It prevents thermal runaway.

[rievax_60]

Re: Yamaha HT-R4065 won't start

The Collector to emitter voltage of the bias transistor at where its turned on enough to bypass the 5ma or so from the voltage amp stage becomes its Vbe multiplied by the resistor divider's ratio.

[tibimakai]

Re: Yamaha HT-R4065 won't start

Thank you so much for the explanations, but it's a bit to much for me.
I will never understand these circuits as well as you. I don't even plan on learning that well.
I have never learned about electronic components, or how they work.
I'm a machinist by profession. I'm more a "mechanical" type guy, who pokes around with electronic devices to keep me busy and make some extra money.
I appreciate a lot, all the help that I'm getting from you. You are a really knowledgeable person.
You asked me in the other thread, if the transistor turns on, I don't even know how would I know if it's turning on or not. I'm just being honest here. I know that a diode opens up around 0.6V. I should have at least 0.6V between the Base and Emitter of the transistor?

[rievax_60]

Re: Yamaha HT-R4065 won't start

The 0.73v on the Base, assuming that the Emitter is firmly tied to ground at 0v,
implies that a reasonable amount of bias current is flowing into the Base.
Also the voltage drop across R319 calculates to 1ma of current.
The transistor's specs say it has a minimum gain of 150. It should be capable of conducting at least 150ma from its Collector pin to its Emitter pin.
If there was no problem and the receiver turned on, I would expect to see about 7.5v at the top of the relay coil and close to 0v at the transistor's Collector pin which is also connected to the bottom end of the coil.
I hope Q302 isnt really fitted?

[tibimakai]

Re: Yamaha HT-R4065 won't start

What do you mean by fitted.
Maybe we should switch back to the the other thread.

[rievax_60]

Re: Yamaha HT-R4065 won't start

What do you mean by fitted.
Maybe we should switch back to the the other thread.

It has dotted lines around it which means that its optional. Its purpose is to shut the receiver down if the mains voltage gets too high.

[tibimakai]

Re: Yamaha HT-R4065 won't start

Some of the transistors are on backorder, I need to wait a little bit more with this receiver.
I guess, I will spend some time with TVs this weekend, and I may replace some speakers in my new Mazda CX5.

[tibimakai]

Re: Yamaha HT-R4065 won't start

I'm trying to get back to this receiver and I'm noticing that I have got a NTE36 and a 2SA1941 transistors. It's a good idea to install this pair, or should I get the matching transistor?

[tibimakai]

Re: Yamaha HT-R4065 won't start

Anybody?
These are the final pair of transistors, at the broken surround channel.
The original pair it was 2SA1941/2SC5198. I can't seem to find the 2SC5198.

[rievax_60]

Re: Yamaha HT-R4065 won't start

The NTE36 should replace the 2SC5198 ok.

[tibimakai]

Re: Yamaha HT-R4065 won't start

After I replace the blown parts, can I just leave out the finals and start it up this way?
If it doesn't blow, then it's safe to install them? This channel, without finals it should make any sound? Can I hook up a speaker to this channel?

[rievax_60]

Re: Yamaha HT-R4065 won't start

You can leave out the output transistors for safe testing. The feedback loop needs to be still closed in the design for the output to balance at zero volts.
In many designs, there are resistors between the driver transistor's emitters and the amplifier output, which completes the feedback path while the output transistors are missing.

[tibimakai]

Re: Yamaha HT-R4065 won't start

Here is the schematic:

[tibimakai]

Re: Yamaha HT-R4065 won't start

Do you think that I could hook up a speaker too? Last time it blew when I hooked up the speaker.

[rievax_60]

Re: Yamaha HT-R4065 won't start

Do you think that I could hook up a speaker too? Last time it blew when I hooked up the speaker.

You can connect a speaker, you need to keep an eye on the signal level at the driver transistor's emitters. It is best not to.
Confirm the output is near zero volts, then measure the voltage difference between where the base of the output transistors would be connected. It should be close to one volt.