Onkyo TX-NR616 won't stay powered on

[tibimakai]

I have picked up this receiver today.
When I turn it on it powers up shows Volume 30 and then turns off.
I took it apart and right away I have noticed the two final transistors were blown. 2SC4468/2SA1695 pair had there plastic body completely blown off.
There is another vertically mounted board which I believe is the pre-amp section of the amp. There is a 22uF/50V capacitor, which it was completely blown out of the board. The aluminum housing it was blown off and some kind of "hair" like stuff it was all over that area and some film pieces from the capacitor too.
I can't find the SM for this unit, but there is available the TX-NR609 at elektrotanya(it's over 17MB). It seems like both are using the same amp, at least at a first glance. I will have to compare them. Amp section is on pages 8 & 9.
It seems that only one channel had a short(Surround rear), the other ones not showing any short.
The 2SA1930 and 2SC5171 pair seems fine. 0.22ohm(dual resistor) resistor seems fine also.
I'm wondering what else could be damaged? I will test all the transistors at that channel, just to be sure, even the resistors.

[JimmysTGP]

I would change out the whole preamp if you can. I played around with a carver receiver that was very similiar. hopefully all that happen was the cap blew which took out the output, but if your luck is like mine the whole preamp took a dump. good luck.

[tom66]

The cap often blows on these. I powered on one with the protect circuit inhibited (foolishly!) and the cap went "pop" quite violently! What happens is the 22u/50V cap gets about 100V across it when there's a fault, and it doesn't really like that. You get a few seconds hissing as warning.

I would suggest you replace all the transistors in the pre-driver section at the same time as the main outputs and avoid using transistors from China if you can, many are fakes.

[tibimakai]

The problem is, that there are 14 transistors including the finals.
Q5416, Q5066 and Q5076 show weird readings. I will have to remove them and measure them outside of the circuitry.
The capacitor that blew up is the C5446 and it's between the two "final" transistors of this board, Q5256 and Q5266.
The TX-NR609 schematic, seems like it matches with the 616.

[tibimakai]

Found the bad components and they are:
Q6056= 2SC4468(2SC5242)-I don't understand why there is a second part #
Q6066= 2SA1695(2SA1962)-same here
Q5416= 2SC1740S
Q5446= 2SA949Y
Q5436= 2SC2229Y
R5476= 82 Ohm
R5366= 18 Ohm
C5446= 22uF/50V
The final transistors I have found at Digikey, but how do I know how matched they are?
The rest of the transistors, I have found only on Ebay. Do you guys I could use some equivalents?

[tom66]

Transistors from Digikey will be fine. They should be matched OK.

Which ones can't you get from Digikey? Maybe some subs/alternatives can be located. As said previously, a great deal of transistors from eBay are fakes. I wouldn't feel right about selling an amp with fake transistors in it. Could just go bad a few days later...

[tibimakai]

I have found only the two finals at Digikey.
I have checked Mouser, Newark. They don't carry these.

[tom66]

Q6056,Q6066 are the finals? The different parts will be subs for each other. But if you use 4468, you must use it with 1695.

[budm]

They are complimentary pair (NPN/PNP) output power transistors, so you need to use them in pair as Tom has suggested.
http://www.toshiba.com/taec/componen...DE_EN_7675.pdf

[tibimakai]

Yes Tom, those are the finals. That small schematic's parts can be found on the main PCB and the other is a vertically mounted PCB plugged in, in a couple of connectors found on the main PCB.
The finals can be found at Digikey. The others are not.



I'm picking up a Yamaha HTR-4065 too.

[tibimakai]

Any input on the rest of the transistors? What do you guys think about NTE equivalents?

[tibimakai]

I have ended up using NTE transistors.
Replaced all the above mentioned transistors, the two resistors and that 22uf capacitor.
The receiver turned on and stayed on like 15-20 seconds and then something smoked from the same channel and turned on. I have turned it on gain and it showed Check speaker wires.
I have checked the transistors that I have replaced and they seem OK.
The 0.22ohm resistor still looks OK. It looks like only the finals are completely shorted each way I'm measuring.
What do you think that I have missed? There are two transistors on the main board and they also look good. Back of the transistors are not touching the heatsink.
I will have to take some pictures.

[tibimakai]

Replaced the two final transistors on the mainboard.
Did not find anything else blown, on the mainboard.
On the pre-amp board, the two previously found R5356(18 ohm) and R5476(82 ohm) were blown again.
But this time, it didn't seem like the transistors were effected.
That is possible that only the resistors are blown and the transistors are not affected?
I can't find a bad transistor on that board. The only difference I'm noticing if I use the transistor checker is between the collector and emitter of the Q5416 compared to other channels. At other channels, shows around 1-1.1mv and this one beeps and it shows 0.75mv. I'm using a NTE85 in it's place of C3198.
I wouldn't like to blow it up again. Any help would be appreciated. If I cut the final transistor's legs, the receiver it's working. I haven't seen any HDMI signal on a TV yet, but I will deal with that later on. Hopefully there are no issues there too.

[rievax_60]

Measure the voltage between C and E of Q5416.

[tibimakai]

I haven't installed back the pre-amp board. I'm afraid that I will blow it up if I would install it and turn it on.
Should I remove the the final transistors and then turn it on?

[rievax_60]

Yes, remove or disconnect the output transistors first.
We also need to close the feedback loop to enable the amp to balance itself. I need to think about this a bit more,

[rievax_60]

Connect NFSBR 9 to the - of C5446.
Short C to E of Q5416.
Replace the burnt resistors you noticed earlier and check all 4 driver transistors for shorts.

[tibimakai]

All the burned components are already replaced. I will have to remove the finals then.
What we are trying to accomplish with these modifications?

[rievax_60]

Originally Posted by tibimakai

All the burned components are already replaced. I will have to remove the finals then.
What we are trying to accomplish with these modifications?

First we want to see that the output will balance to zero volts.
If all looks ok without the same resistors burning out again, we can then have a closer look at the bias circuit for problems.
The short between C and E on Q5416 makes the bias circuit safe for now.
The idea is to be certain that all is ok including the bias circuit before the finals are connected.

[tibimakai]

So, I did those connections and nothing blew up.
Where should I measure the output, at +BSBR23 AND +BSBR22?
If yes, then at those points I'm measuring -.001V/-.003V.