Hello all, newbie to forum but I will be asking a lot of questions here in the foreseeable future
I am really into tinkering with things and I got an AV receiver for free because it doesn't power on. Model is Onkyo TX-SR603X and when plugged in the standby light flashes for a split second and then nothing happens no matter what. I inspected everything inside and it looks okay to the naked eye but I am not too experienced with detailed circuit troubleshooting. From what I have gathered on the interwebz this is likely related to the standby circuit having a bad relay which seems to make sense. I was wondering if I can bypass the entire standby circuit so that the unit is always on when plugged in, that way I can use it meanwhile until I get a more permanent solution (cough Pioneer cough).
A little bit of digging around later I found the service manual for the receiver which would probably seriously come in handy if I knew how to read diagrams and the like. Anyway here is an attached picture of something I think might work, but I've already taken 120v to my hand once tonight (PSA for the kids, always remember to check to see if sh*t is plugged in before you go sticking hands and metal tools inside things) and don't want to risk damaging anything further if the standby board is not the problem. The cut off diagram on the bottom right goes to the "High Current Power Supply" as stated on the piece in large friendly lettering so basically I would be putting the 120v straight into that and the power switch wouldn't work... but I am wondering if there is any kind of manipulation of the power before it gets to the PSU? Would it be better to bypass only the relay (RL901)? Please let me know if this can work and second-most importantly, if it is safe!

Thanks
Miklos

 

The fact that one of the output connections connections is marked "MPUGND" makes me think that the U07 board supplies power to the micro controller that controls the device. Have you checked the output voltages from this board. If I am right then just enabling the main power supply without the micro controller running will not achieve anything.

Les.

 

The fact that one of the output connections connections is marked "MPUGND" makes me think that the U07 board supplies power to the micro controller that controls the device. Have you checked the output voltages from this board. If I am right then just enabling the main power supply without the micro controller running will not achieve anything.

Les.

No multimeter D: there's gotta be something I can jump with a simple wire-soldering to make this thing think it's alive. I do it on cars sometimes... (I'm a mechanic not a car thief ) What about the relay? Replace with a piece of wire?

 

No multimeter D: there's gotta be something I can jump with a simple wire-soldering to make this thing think it's alive. I do it on cars sometimes... (I'm a mechanic not a car thief ) What about the relay? Replace with a piece of wire?

Sorry for double post but is what I highlighted correct...? They are the same thing on the two diagrams?

 

I don't see how you can start electronic fault finding without a multimeter.

Les.

 

I don't see how you can start electronic fault finding without a multimeter.

Les.

It gives me something to do at midnight. I need my music -.-

 

I don't see how you can start electronic fault finding without a multimeter.

Les.

Starting is the easy part homie, it's finishing successfully that's the fun part

 

First, please realize this unit can give you a nasty shock even when its not plugged in. The capacitors on the main board and SMPS standby board will do you bad. Don't stop your heart at midnight when no one is around. They will find you in your underwear foaming at the mouth with a wet load in your undies.

Secondly, check the service manual for reading out the PROTECT mode error. The system will tell you why it shut down and is blinking the light. Follow the troubleshooting guide for the error in the service manual.

Secondly, look for burnt parts. There are fuses on the boards, are they still in tact?

Its hard to do anything more without a multimeter. You can get a pretty good one for coffee money on Amazon. I happen to like this one for $16 dollars. Does almost everything my $500 Fluke does. https://www.amazon.com/Auto-Ranging-Digital-Multimeter-Continuity/dp/B07KPBGR3R/.

You can check for shorts, diodes and other discrete parts following the circuit. I would start doing a diode test on the output and bias transistors to see if a channel is blown.,

IF the error message was a DC PROTECT, its likely a blown output section of one channel of the amplifier. Unless you want to get into learning to solder and desolder it's time to hire a tech.