Onkyo TX-SV646 static in left and right channels, please help!

[Laricc]

Hello, I recently got an Onkyo TX-SV646 receiver from a friend, and when I started the unit up, I was met with a loud static/popping sound coming from the left channel. The sound could be heard on the speaker outputs, along with the headphone and pre-outs. I took the unit down to one of my friends who worked with ham radios and circuitry so he could take a look at it, though he also could not find out what the problem was. I recently took it down to someone who lived close by that could fix old units such as these, though he also found it hard to find the issue. In the end, he said he didn't want to rip me off by price and said the parts usually need to repair old units cost around the same price as the unit. I finally took some steps back and asked one of my friends where to look for help and he turned me to the forums.

The main problems that I am dealing with are that the receiver has a loud static/popping in the left and right channels. The right channel recently started to get a similar static like the left channel, though not as intense. Note that both statics are not the same. The static in the left channel lasts 5 seconds after the unit is shut down while the right channel lasts 2-3 seconds. The static will now and then cut out completely, only to come back after a few minutes. The static stays at the same volume and doesn't change if the volume is turned up or down.


I am not too experienced with circuitry noir soldering, though I know some people who could help me out with that.

~Thanks.

 

[Tom B]

Hello,
The problem you are experiencing could be noisy differential amp transistors. Small 3 pin 2SC1845 transistors found on both amplifier boards. But this unit is a "5 channel" unit with RF, RR, LF, LR, and center channels. You need to conform which of the 5 are noisy. So set the unit to one of the surround modes and check all 5 channels. You can use speaker to see which channels. As a confirmation of the channels use a voltmeter to check for DC on the speaker output + when the noise occurs. Anything spiking above 0.5v can cause protect to disengage speakers.
If you find this situation on one or more channels, I would go ahead and replace all these differential amp transistors. The are 2 for each channel, and 5 channels, so 10 transistors total. (Q501, Q503, Q502, Q504, Q1501, Q1503, Q601, Q603, Q602, Q604). You can get onsemi replacements (KSC1845) from Mouser real cheap.

 

[Laricc]

Hello,
The problem you are experiencing could be noisy differential amp transistors. Small 3 pin 2SC1845 transistors found on both amplifier boards. But this unit is a "5 channel" unit with RF, RR, LF, LR, and center channels. You need to conform which of the 5 are noisy. So set the unit to one of the surround modes and check all 5 channels. You can use speaker to see which channels. As a confirmation of the channels use a voltmeter to check for DC on the speaker output + when the noise occurs. Anything spiking above 0.5v can cause protect to disengage speakers.
If you find this situation on one or more channels, I would go ahead and replace all these differential amp transistors. The are 2 for each channel, and 5 channels, so 10 transistors total. (Q501, Q503, Q502, Q504, Q1501, Q1503, Q601, Q603, Q602, Q604). You can get onsemi replacements (KSC1845) from Mouser real cheap.

Thanks for the reply, I tested the receiver from the speaker outputs like you said, and I was reading 0.05-0.07 on the right channel. I was reading 0.02 on the left channel, until the static suddenly ceased, making the left speaker output channel read 0. I had no other forms of static from the other channels, it only seems to be in the left and right channels.

The surround right channel was also getting numbers, like the right main channel, though they were in the 0.04-0.05. I also got a reading out the center speaker, what was around 0.03. suddenly all static died away and I was reading in the negatives from the right channels and the center channel, one other thing was that the right channel, plus the surround right channel continued to read 0.03 when the static died away, while the center read -0.02.



The static only seems to be coming from the front left and right channels.




I used 20 DC V on the voltmeter to test the speaker output.

 

[Tom B]

While it could still be the differential transistors, I am not sure because usually when they get noisy, you will usually get fluxuating DC on the speaker outputs as the noise occurs. But your voltage seems to be staying constant and very low. With noise, you can usually see voltage increasing to a volt or more, sometimes engaging the protect circuit.

 

[Laricc]

While it could still be the differential transistors, I am not sure because usually when they get noisy, you will usually get fluxuating DC on the speaker outputs as the noise occurs. But your voltage seems to be staying constant and very low. With noise, you can usually see voltage increasing to a volt or more, sometimes engaging the protect circuit.

I was getting some flux on the channels when the static sound started. I will probably order the transistors for the receiver and see where that gets me, though should I replace all of them or just the left and right channels. If it is the left and right channels, which ones are they on the circuit board?

And the model is KSC1845, because at the beginning you said they were 2SC1845 transistors, just want to be sure.

Thanks again.

 

[Tom B]

Q501 and Q503 are for the left channel, and Q502 and Q504 are for the right channel. They are small 3 legged transistors. I am assuming that they are regular transistors and not surface mounted ones. They show on the schematic as 2SC1845. Fairchild (On-Semi) replacements are KSC1845. They should be the same, but verify that the pin outs are the same ECB, but I believe they are.

 

[Laricc]

Alright, thanks for your time. I'll get back to you if there are any other problems I run into. I'll probably get the 2SC1845 and go with that. I found some on the internet and I took a look inside the unit. I found the transistors and I'll be replacing them when I can get the chance.

 

[Laricc]

I tested the unit again and it stayed at 0.01-0.02 20 DC V, so I took it down to 2000m DC V and I was reading 005-020 on the left channel, the one that had the static, and I compared it to the right channel what stayed at 025 and never changed. I will soon be replacing the transistors once I have them ordered.