Help with Onkyo TX NR 838

[Mogli1476]

Hey @all,

i'm a very happy user with my Onkyo Receiver but yesterday Channel R was exploded and smoke come out of the receiver.

After opening i saw the two broken AMP Transistors TTA0001 and TTC0001. I also checked the Pre AMP Board and found a lot of broken parts in there. The SM from elektrotanya helps me to find all errors and parts.

After ordering all parts i removed the broken ones and replaced all parts with the new ones. I changed also the white resistor in front of the TTA/TTC which was broken too.

After i think everything was good i tried to perform a first test. Powering on without the Pre AMP Board. Good idea because i works again. The Relais were clicking and the Receiver turned on. I'm very happy and everything seems Ok. The Receiver was not getting warm after testing a while.

Then i turned everything off, remove the power cord and install the Pre AMP Board.

I build one cable with two 100k resistors for measure the idle current and clamped this cable to the Voltmeter. First to the broken Channel R.

Carefully i turned the receiver on and it works. The Voltage after turning on was 4mV. I adjust it to 2,5mV like the SM says. And so i checked one channel after the other, adjusted every channel and everything seems Ok. After 4-6 min. warm up time I adjusted again to the values named in the SM. But the values are not reached. The SM says adjust from 9 - 11mV L/C/R Channel and from 6 - 8 mV all other Channels. I'm turning the adjustment potis to the max. and i'm getting max. 8mV at L/C/R and 5mV at the other Channels. I'm not sure to turn the potis to much.
After waiting a while everything looks good.
But the Pre AMP Board was getting very warm and so i thought it was better to turn the receiver off.

Later after testing i was going to the living room, install the HDMI Out cable from my Receiver to the Flatscreen and turn the receiver on.

Not a good idea because a loud Bähhhm and smoke comes out from the R Channel. Damn it!! What was happened? I cannot explain myself.

Then I disassemble the whole Receiver to measure every part again and the whole problem was coming back. TTC/TTA, the capacitor and all the parts on the Pre AMP Board were died again. But i had replacement parts in stock. Measured everything and changed everything again.

And again everything is looking good after turning on without Pre AMP Board. Now i checked all parts on the Pre AMP Board again and it looks good.

Then i installed the Pre AMP Board again and turn the receiver on. From the first time nothing happened and it will turn on on is working like it should. But after a few seconds little bit of smoke is coming from the Pre AMP Board (SL Channel) so that i turn it off and remove the power cord as soon as possible.

Nevertheless some parts like in the R Channel were died, this time in the SL Channel, and i have to remove them too.

So, before my next try to burn some components again i will be sure to remove every error from the Pre AMP Board and adjust the idle current before turning on.

Can anybody help me in this case? How to adjust all the potis for idling without installing the Board and how to check the whole Pre AMP Board correct to prevent the next explosion?

Thanks and best regards

[mmartell]

Re: Help with Onkyo TX NR 838

You'll have to go over every part in the bad channel on that preamp board. Very strange that you couldn't adjust ALL channels to the proper spec without going to the end-of-travel though. Check the schematic for commonalities.

[Khron]

Re: Help with Onkyo TX NR 838

I build one cable with two 100k resistors for measure the idle current and clamped this cable to the Voltmeter. First to the broken Channel R.

What i'm seeing in the service manual is two 100 ohm resistors, not 100Kohm.

Did you mis-type that, or did you really use two 100K's in your cable?

PS: Can't really see the point in adding those 100ohms there, most voltmeters already have a 1-10Meg input impedance anyway...

PS2: Where did you get the replacement parts from?

[Mogli1476]

Re: Help with Onkyo TX NR 838

What i'm seeing in the service manual is two 100 ohm resistors, not 100Kohm.

Did you mis-type that, or did you really use two 100K's in your cable?

PS: Can't really see the point in adding those 100ohms there, most voltmeters already have a 1-10Meg input impedance anyway...

PS2: Where did you get the replacement parts from?

No no, this was naturally a mis-type. I was using 100ohm resistors.

Some parts like the TTA004 / TTC004 are from mouser.com and the others like TTA0001/TTC0001 and 2SA1037 / 2SC2412 are from ebay.

[Mogli1476]

Re: Help with Onkyo TX NR 838

You'll have to go over every part in the bad channel on that preamp board. Very strange that you couldn't adjust ALL channels to the proper spec without going to the end-of-travel though. Check the schematic for commonalities.

Yes, first i checked every part in the R Channel and now the R Channel is working but the SL Channel not.
Is it possible that wrong idling current (wrong adjustment of the poti) occurs the explosion of some channel parts?

Do you have an Idea what components can responsible that i cannot reach the proper spec?

[tibimakai]

Re: Help with Onkyo TX NR 838

You have replaced the finals, the 0.22 Ohm resistors as well, right?
Tighten all the final transistors, they are most likely a bit loose.
Yo will have to pay attention to each part, measure them carefully, I'm pretty sure, that you have missed some parts.
I don't have the schematics in front of me and I have never worked on the 838, only on 636, but usually, 33 Ohm resistors, 2.2 Ohm, 82 Ohm, there is a surface mount above the two surface mount transistors next to each other is bad(0.820 Ohm ?!, not sure about the value). I have learned, to compare the readings, with the neighboring channels. Once, I have mixed the transistors and that is how, I blew up the channel again. I was using different transistors, than the originals.
Try to get transistors from Mouser, Digikey. I wouldn't trust Ebay transistors, maybe they are fake.

[Mogli1476]

Re: Help with Onkyo TX NR 838

You have replaced the finals, the 0.22 Ohm resistors as well, right?
Tighten all the final transistors, they are most likely a bit loose.
Yo will have to pay attention to each part, measure them carefully, I'm pretty sure, that you have missed some parts.
I don't have the schematics in front of me and I have never worked on the 838, only on 636, but usually, 33 Ohm resistors, 2.2 Ohm, 82 Ohm, there is a surface mount above the two surface mount transistors next to each other is bad(0.820 Ohm ?!, not sure about the value). I have learned, to compare the readings, with the neighboring channels. Once, I have mixed the transistors and that is how, I blew up the channel again. I was using different transistors, than the originals.
Try to get transistors from Mouser, Digikey. I wouldn't trust Ebay transistors, maybe they are fake.

Yes, thats true. I changed and checked them if its necessary after changing TTA / TTC. If i don't change them it was impossible to turn on the receiver. But after fixing all components on the main AMP Board the Receiver was running without any problems disassembled the Pre AMP Board. That was a note for me that the AMP Board is working well.

Additionally after changing all TTA/TTC Transistors I lift up every single Transistor and renew the heat paste behind. After that I fixed all Trans. again.

I have checked the whole Service Manual and changed every part which was broken on the Pre AMP Board. But i did that only on the R Channel because this was the only channel where the TTA/TTC were burned. I ordered 5 TTA and 5 TTC in a collection from ebay seller. On the topic i also changed the TTA/TTC from the C and the L Channel i hope that the channels sounds all equal.

To Check channel R I also compare channel L and C with each other like you wrote. That sounds for me the best solution to be out of errors. But i think a mistake i did was to adjust all channels new to get the values like the SM. After waiting the warm up time i adjust all potis to the max. position and the the problems came back like burning channel R and now channel SL again.

As a matter of fact I am using different Transistors. This could be a reason for the Problem, or not? At the moment all channels except the R, C and L channel we using the Transistors which i bought from ebay. The other channels have the old ones installed.

It was nearly impossible to get TTA and TTC Transistors except the ebay seller. Mouser only have TTA / TTC 0002 Transistors but they are very large. But the characteristics are nearly the same. I ordered one of them to check if they fit into the receiver. But at the moment i don't.

What do you think about adjusting the wrong idle current? Is it possible to destroy the Pre AMP Board by wrong adjustment?

Best regards!

[Mogli1476]

Re: Help with Onkyo TX NR 838

After a short investigation i found the first wrong parts i think. I was using 2SC2412K with SMD Code BS and not BR. That means another DC current gain. And also the 2SA1037AK has the wrong DC current gain. I think this could be one first problem i had.
I'll fix this soon and give a reply to all.
Best regards, Mike

[tibimakai]

Re: Help with Onkyo TX NR 838

Usually, when something blows a bit later, is a missed resistor somewhere.
You can adjust the pots to zero, and start all over and adjusted again.
I have a thread here, asking about transistors for a TX-NR636. There, I mention what transistors I'm using.

[Mogli1476]

Re: Help with Onkyo TX NR 838

Usually, when something blows a bit later, is a missed resistor somewhere.
You can adjust the pots to zero, and start all over and adjusted again.
I have a thread here, asking about transistors for a TX-NR636. There, I mention what transistors I'm using.

Ok, but i'm not sure in which direction i have to turn to find the zero position. But first i have to order new TTA0001 and TTC0001 for every channel to have the same transistors all over.

But its not possible to get the TTA/TTC 0001. I found TTA/TTC 0002 at mouser with similar values. It's a little bit larger but i will check if it fits. What do you think?

Thanks for the link to your 636 thread. A lot of needful informations there.

[mmartell]

Re: Help with Onkyo TX NR 838

Having to max out the adjustment pot in all channels suggests a problem in your procedure. Did you follow the instructions properly ?

In any event turning the pot fully counterclockwise will start you at zero.

By the way, check the battery in your meter.

[tibimakai]

Re: Help with Onkyo TX NR 838

Why do you want to replace all the transistors, at other channels. They are good, live them alone.
In Germany, you don't have Digikey? Not to long ago, I have purchased those transistors from them. They did not have them for a while, then I have used 2SA1507/2SC3902. They were discontinued after a while, and now they have again the TTA/TTC transistors back in stock.
I don't understand, why did you adjust all the pots at other channels? If something is not broken, don't touch it. You don't have that saying in Germany?
As mmartell said, adjust them all the way counterclockwise(left).

[Mogli1476]

Re: Help with Onkyo TX NR 838

Why do you want to replace all the transistors, at other channels. They are good, live them alone.
In Germany, you don't have Digikey? Not to long ago, I have purchased those transistors from them. They did not have them for a while, then I have used 2SA1507/2SC3902. They were discontinued after a while, and now they have again the TTA/TTC transistors back in stock.
I don't understand, why did you adjust all the pots at other channels? If something is not broken, don't touch it. You don't have that saying in Germany?
As mmartell said, adjust them all the way counterclockwise(left).

Thats what you wrote in Post 6 ... "Once, I have mixed the transistors and that is how, I blew up the channel again"
I thought it was better to replace all Transistors. But that was only an idea and if i have disassembled the main board its not more work for me to change all the other Transistors. Price per each is only 1,80€.

Now i understood that was not a good idea to adjust all other potis. But during the new measurement of idle current on each channel the values are not exactly like in the SM. Thats the only reason to adjust all channels again.

I will try to adjust all channels again like your suggestion. But first i have to wait for my order of 2SA1037 and 2SC2412.

Best regards, Mike

[Mogli1476]

Re: Help with Onkyo TX NR 838

Having to max out the adjustment pot in all channels suggests a problem in your procedure. Did you follow the instructions properly ?

In any event turning the pot fully counterclockwise will start you at zero.

By the way, check the battery in your meter.

Ok! Thats what i thought too. I read and respect all instructions carefully and was really sure not to forget something.

I have two meters and all the meters were showing the same results.

Will try the adjustment like you said. But first i have to wait for my ordered parts. Best regards

[Mogli1476]

Re: Help with Onkyo TX NR 838

Ok, but i'm not sure in which direction i have to turn to find the zero position. But first i have to order new TTA0001 and TTC0001 for every channel to have the same transistors all over.

But its not possible to get the TTA/TTC 0001. I found TTA/TTC 0002 at mouser with similar values. It's a little bit larger but i will check if it fits. What do you think?

Thanks for the link to your 636 thread. A lot of needful informations there.

Anybody a solution for that? Is it Ok to take TTA/TTC0002 instead of TTA/TTC0001?

Best regards.

[Mogli1476]

Re: Help with Onkyo TX NR 838

Hello @all!

Yesterday my Receiver seems to be fixed and everything was running without explosions. I adjusted channel by channel to the required Voltages. When i came to channel R and wanted to turn the adjustment poti, nothing happens. All other channels are adjustable but the R channel not.
I don't know why.
Today I start to examine the problem and will post it here.
Regards, Mike

PS: Does anybody know where to buy the white 0,22Ohm resistors in front of the Main Trans?

[tibimakai]

Re: Help with Onkyo TX NR 838

You still have a bad component in there somewhere.
Last time, I have found them on Ebay. I'm out of them right now, I will have to buy new ones as well.
Now you had the right voltages, when you were adjusting the idle current?

[Mogli1476]

Re: Help with Onkyo TX NR 838

You still have a bad component in there somewhere.
Last time, I have found them on Ebay. I'm out of them right now, I will have to buy new ones as well.
Now you had the right voltages, when you were adjusting the idle current?

Yes! I found another broken main amp Transistor and the 820 ohms resistor. But i have to wait for my order at mouser.com

If you have found any trusted source for this white resistors, let me know.

I'm not sure to get the right current after warm up because i only adjusted immediately after power on to 1,5 and 2,5mV. Tomorrow i will check the values after 4-6mins. and hopefully i can readjust them to the voltages in the SM.

Regards, Mike

[tibimakai]

Re: Help with Onkyo TX NR 838

When it is all good, the voltage has to rise pretty slow. If it raises to fast, or not at all, than something is still bad.
I will look for those resistors, but I'm in the US.
It is pretty expensive:
https://www.ebay.com/itm/Metal-Plate...-/162885479909

[tibimakai]

Re: Help with Onkyo TX NR 838

http://www.analogmetric.com/goods.php?id=1534