Onkyo TX-NR636 Protection Mode - thermal issue?

[curiousgeorge1]

Hi folks,

I have a Onkyo TX-NR636 that goes into Protect mode (the display lights up upon pressing on/standby, but 'clicks' off within 2-3 seconds).

Using the Service Information Mode (in the service manual attached, page 11), the service information display shows: T -42C 17 04

This indicates the power off cause is 'Thermal Protect' and the temperature reading is negative 42 degrees celcius.

Using the instructions for 'Confirmation of output voltage and thermal sensor' on p 12 of the service manual, the display shows: >00 -47 F:x S:H

Does anyone know what might cause the temperature reading to be so low?

Any tips, suggestions or even resources that I could use to fix this would be much appreciated. I am a beginner and keen to learn more.

Thanks for your time.

[tibimakai]

Re: Onkyo TX-NR636 Protection Mode - thermal issue?

I have repaired quite a few of these, and I have never even check that service information.
Every time I had blown components, at the amp.
I open them, and go right away at the final transistors on the heatsink, to check for short.

[R_J]

Re: Onkyo TX-NR636 Protection Mode - thermal issue?

That seems like an odd temperature (-47) it could be a data error, Have you tried a master reset on the amp?

[redwire]

Re: Onkyo TX-NR636 Protection Mode - thermal issue?

Q6300 (LM61) is the analog temperature sensor on the little board, I would check the cables, mounting, it's output voltage to the MCU. At 25°C it would give 0.850VDC. If the MCU got 0V that might be -42°C.

I found Onkyo's don't work properly with the back panel removed, many of the boards rely on it to provide proper grounding. I had one always going into PROTECT mode even after I'd fixed everything until I noticed one board was not grounded, when taking voltage measurements. The RCA/HDMI connectors ground the boards to the case.
So using jumpers between the RCA's/HDMI on the board stack and main amp ground allowed me to keep going.

[curiousgeorge1]

Re: Onkyo TX-NR636 Protection Mode - thermal issue?

Hi everyone,

Thanks for your comments above and for your contributions to other Onkyo threads in this forum - it gave me some good context diving into this.

To give you an update, I have some progress (I'm saying that tentatively, not having used speakers for an extended period yet).

I checked the transistors on the heat sink and the adjacent resistors on the main board, as recommended in here and other threads. I couldn't find any fault with these.

However, I removed the thermal sensor (Q6300) that attaches at a right angle to the heatsink. I think the issue was a solder that correlates to the 'Thermal' line represented in the diagram attached.

The solder had two 'tips', one of which was very fine and was in contact with the (plastic?) casing that attaches the 3 leads to the small board. It appeared they had melted together ever so slightly. There was no discoloration on the board that I could see. I filed the solder down so that they were no longer in contact and reassembled. Apologies for my poor terminology, but that's my best description without having a picture.

The receiver turned on, no safety mode was activated and the temperature reading in the service information mode is now 27°C.

Any ideas why this might have happened or how I might avoid this in the future?

Thanks again for your responses.

[redwire]

Re: Onkyo TX-NR636 Protection Mode - thermal issue?

It sounds like a manufacturing defect. Those little boards are are usually hand assembled and the soldering can be poor quality or things melted a bit if they did use wave soldering.
Melting things (after soldering) would need heat over say 120°C which is above what the transistors can take, so not likely to happen in real use. The Onkyo's can't do club/dance duty for more than a song or two.