Hi folks. I have an Onkyo TX-SR608 amplifier, it has a defect for a few days. When switched "ON", it works perfectly. If I turn "off", in standby mode, the power relay makes continuos "clicks" for several minutes, often disappears, then comes back. I noticed that when it "clicks", the voltage on the output main transformer rises and falls, without the click, the voltage is correctly zero. If I activate the "hdmi pass-trought" mode, where the relay should stay active even when amplifier in off/standby, if I hear the "click", the voltage rises and falls, when the "clicks" stops the voltage stabilizes correctly . If I turn on the amplifier no "clicks" and I have the correct voltage. I checked the power relay, the resistor R921 47R (is 46.7R) are ok. I was thinking of a defect in the KRC105S transistor, which manages the relay. But when turned on, amplifier works perfectly so I don't think it is. A strange, if I hold down the standby/on button, the clicks stops! if I release the button, the clicks return! Have any of you had a similar problem? I have searched the net, but I have not found any matches. Thanks for your any help. I attached schematic.
Start by checking R921 (47ohm 1/2 watt resistor) on the power supply board. It should read very close to 47 ohms. If it is lower by even 2-3 ohms it can cause this type of issue. While you are in there, also check D925
Post by hiroshi976 on Jan 22, 2021 10:21:17 GMT -5
R921 is 46.6Ohm. But how come when it's ON, works perfectly, no "clicks", everything perfect? In your opinion, try to see if the 12v go up and down between points 1-4 of JL901A? I suspect it is the fault of transistor Q181, or some pulse it must receive, when pressing OFF / STANDBY.
Most people don't realize that an Onkyo receiver is "on" the moment you plug it in. The Main CPU never turns off. The way this circuit works is that when you press the "on/standby" button, the Main CPU sends a signal to the main relay. "Signal" isn't really the right word because what the Main CPU does is to exert a small voltage to the base of Q181 which then ties the "MPowerD" line to ground. The relay is always receiving power from a 12V source (R921 is supposed to bring this power down to 9V) so when the other side of the relay sees the ground from the Main CPU (through Q181), it turns on the Main Relay which in turn powers up the Amp and the Digital sections (2 different subsystems). Onkyo does this because it allows the Main CPU to check the outputs of the Main AMP before applying full power to ensure there are no blown channels.
The fact that it doesn't click when it is running merely indicates that the relay is properly energized and is operating as it is supposed to. The fact that it clicks when off indicates that the relay is seeing a ground signal on the "MPowerD" line.
There are only two other items in this circuit. There is a diode (D925) that provides protection for the relay and there is a small capacitor C902. both of these tie between the 12V (actually 9V) source and the output line so there is no way for either of these to cause the issue you are seeing so the only thing left would be Q181. I suspect this part is failing and is switching the MPower signal to ground without receiving the signal from the Main CPU.
Last Edit: Jan 22, 2021 14:39:13 GMT -5 by tjmotter
Post by hiroshi976 on Jan 22, 2021 16:26:43 GMT -5
Hi thanks for the help, and the time dedicated to me. I know how the power supply amp works. Unfortunately I have checked it, the problem is on the Q181 transistor. The power supply is perfect. Unfortunately the "base" of the Q181 transistor receives the up-down voltage 0-3V pulse randomly, when I turn it off, or put it in standby mode. Even though I enable "HDMI Passtrought" mode, which is supposed to keep the amp powered, I get this "clicks" randomly. When the clicks stop, I read "0.150v" on the base. If I turn on the amplifier have 3v on the base of the Q181, voltage remain fixed and stable. What can I check? Thank you very much for helping
Last Edit: Jan 22, 2021 17:08:21 GMT -5 by hiroshi976
Based on your symptoms, the only thing I can see that could affect this is the Main CPU itself. The thing is these rarely fail so if I were working on it I would try to do a full reset to the system to see if that solves the problem. It is possible that the system is confused somehow and a full reset would bring it back to the factory settings.
To perform a reset, press and hold the "VCR/DVR" button and then press the "On/Standby" button. The display should show "Clear" and then shutoff. Once you have completed this step, set the unit up with the settings you prefer and test it again.
It was my first attempt, restore/reset the system. Do you think to i upgrade/rewrite the firmware? If possible. There must be a combination of standby/off-passthrough and ON that affects this. Why doesn't the 3v fluctuate in ON? If I turn off and hold the button, I don't have the problem
Edit. firmware upgrade/refresh done! procedure was successful, no errors. But the problem persists. in your opinion could it be the Q704 FETs? Could it send pulses when it shouldn't?
Last Edit: Jan 23, 2021 5:48:39 GMT -5 by hiroshi976
Hello. here I am again,yesterday I disassembled the MPU-Board. I checked it, and perhaps, I found the anomaly. Randomly, in Q181, a short circuit occurs, between Collector and Emitter. Another strange thing, I find myself, with the amplifier OFF, have 12v on the Q181 collector. If I turn it on, it goes back to 0v (approx). There shouldn't be! Shouldn't D925 block everything? Then, why 12v? Why isn't it under load? Anyway I decided, I change Q181 and D925, relay looked ok, the coil was 540Ohm. I would not want it to be defect, which occur randomly. I ask you, can I replace D925 with normal diode? I have no smd diode. Thank you.
Last Edit: Jan 24, 2021 6:36:08 GMT -5 by hiroshi976
The 12V on the collector is normal. It is simply feeding the voltage through the relay. Once the collector goes to ground it triggers the circuit. The relay is simply a piece of wire so when there is no ground, you will always see 12V on this line. In reality, this voltage should drop to 9V once ground is applied because the 47ohm resistor will pull the voltage down. The diode is there simply to protect against the inrush current when the transistor switches to ground.
I suggested replacing Q181 near the beginning of this thread but you insisted it was working properly. Change it and let us know what happens.
Last Edit: Jan 26, 2021 13:37:33 GMT -5 by tjmotter
Post by hiroshi976 on Jan 27, 2021 13:46:30 GMT -5
thank you for the answer. I don't wish I had misled you. The power relay, when as the Q181 transistor closes ground circuit, the amplifier works perfectly. If I turn ON the amplifier, I have no problem, everything works fine! I have the problem in standby or if I activate the hdmi-passtrought mode, in that case, on the base/gate of the transistor Q181 arrive, making up and down, floating, the 3v ((0~3~0~3V ecc). So the main tension goes up and down and I hear the clicks! If I turn ON the amplifier, the Q181 transistor receives the 3v on the gate, relay works correctly. Now I am waiting for the spare Q181 transistor, but I suspect a problem related to the standby mode, I am only sorry that I was unable to decipher/understand in standby/passtrouh zone the schematic.
Last Edit: Jan 27, 2021 13:49:04 GMT -5 by hiroshi976
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