Post by serafis on Apr 18, 2024 16:45:46 GMT -5
I'm trying to fix an Onkyo TX-NR636 that won't power on. Service manual can be found at elektrotanya.com/onkyo_tx-nr636.pdf/download.html
My initial diagnosis found that Q7018 (BU33TD3WG-TR 3.3V 200mA regulator) on the back of the HDMI board had failed. Its output pin was fluctuating between 4.2 and 6V, and resistance between pins 1 (input) and 5 (output) was only around 84 ohms. And the MPU was making a faint sort of 'crackling' sound - not good!
I removed Q7018 and checked resistance between the board's VOUT pad and GND pads to make sure there wasn't a short further down the line that might have caused the regulator to fail. It measured around 20K which seemed reasonable.
I didn't have one of those regulators available, but I did have some TLV74333PDBVR's, same pinout, 300mA, so I put one in to see what would happen. Applied power, and measured 3.3V at Q7018 output, so I reinstalled the board and the receiver did power up, so the MPU wasn't fried.
I reset to factory settings, and then front display showed a "speaker type" message which I responded to by pressing Enter. Then I got a "Wait" message, so I did. But after several minutes, the display went off and the main relay started clicking on, then off, then on, then off at around 0.5-1 second intervals.
I rechecked the TLV74333PDBVR (Q7018) and it too had blown, this time shorting between pins 1 and 5. The datasheet says that short circuit current should only be 150mA and output short circuit duration is indefinite, so this failure was rather unexpected.
Anyway, I put another one in and checked the 3.3V output, but the main relay still just clicks on/off/on/off, and pin 126 on the MPU (MPower) pulses at the same rate - which I expected as it operates the transistor Q7017 that switches the relay.
So I'm stuck. I suspect the MPU may be fried, but I don't really know how to check this, or why the regulator failed, or where to go from here. So any help greatly appreciated.
My initial diagnosis found that Q7018 (BU33TD3WG-TR 3.3V 200mA regulator) on the back of the HDMI board had failed. Its output pin was fluctuating between 4.2 and 6V, and resistance between pins 1 (input) and 5 (output) was only around 84 ohms. And the MPU was making a faint sort of 'crackling' sound - not good!
I removed Q7018 and checked resistance between the board's VOUT pad and GND pads to make sure there wasn't a short further down the line that might have caused the regulator to fail. It measured around 20K which seemed reasonable.
I didn't have one of those regulators available, but I did have some TLV74333PDBVR's, same pinout, 300mA, so I put one in to see what would happen. Applied power, and measured 3.3V at Q7018 output, so I reinstalled the board and the receiver did power up, so the MPU wasn't fried.
I reset to factory settings, and then front display showed a "speaker type" message which I responded to by pressing Enter. Then I got a "Wait" message, so I did. But after several minutes, the display went off and the main relay started clicking on, then off, then on, then off at around 0.5-1 second intervals.
I rechecked the TLV74333PDBVR (Q7018) and it too had blown, this time shorting between pins 1 and 5. The datasheet says that short circuit current should only be 150mA and output short circuit duration is indefinite, so this failure was rather unexpected.
Anyway, I put another one in and checked the 3.3V output, but the main relay still just clicks on/off/on/off, and pin 126 on the MPU (MPower) pulses at the same rate - which I expected as it operates the transistor Q7017 that switches the relay.
So I'm stuck. I suspect the MPU may be fried, but I don't really know how to check this, or why the regulator failed, or where to go from here. So any help greatly appreciated.
