Post by serafis on Mar 7, 2024 15:56:33 GMT -5
Success at last! I managed to source some HN4A06Js (Q770) from Aliexpress at not too great a cost. A bit fiddly to replace, given its size and the number of other SMDs in close proximity, but thanks to ChipQuik and patience, I managed to do it. Unfortunately no difference, so maybe not fried after all, just looked bad.
So then I thought again about what might cause R768 to read 47K differently from other channels (thanks madmal!).
I traced the PCB from the +ve of C763 through various tracks, resistors and via holes to R768. I eventually discovered that one of the via holes had no contact with the other side of the board, so carefully drilled through it, scraped the tracks on either side of the board to expose the copper and soldered a fine piece of wire through the via hole to the tracks on either side.
Measured R768 and it now read similarly to the other channels, so put it all back together and powered it up. Bingo! No PROTECTOR mode.
Not sure what was going on with the earlier screwy voltage measurements, but all channels working now. Right Surround channel measures a tad higher DC than the other channels (10mV as opposed to 2-4mV) but I think I can live with that. Now to give it a soak test before final reassembly, but all looking and sounding good at the moment.
Thanks for all the help, much appreciated. Now on to the next project!
EDIT: After an hour or so, Right Surround DC settled down to around 4mV, similar to other channels.
So then I thought again about what might cause R768 to read 47K differently from other channels (thanks madmal!).
I traced the PCB from the +ve of C763 through various tracks, resistors and via holes to R768. I eventually discovered that one of the via holes had no contact with the other side of the board, so carefully drilled through it, scraped the tracks on either side of the board to expose the copper and soldered a fine piece of wire through the via hole to the tracks on either side.
Measured R768 and it now read similarly to the other channels, so put it all back together and powered it up. Bingo! No PROTECTOR mode.
Not sure what was going on with the earlier screwy voltage measurements, but all channels working now. Right Surround channel measures a tad higher DC than the other channels (10mV as opposed to 2-4mV) but I think I can live with that. Now to give it a soak test before final reassembly, but all looking and sounding good at the moment.
Thanks for all the help, much appreciated. Now on to the next project!
EDIT: After an hour or so, Right Surround DC settled down to around 4mV, similar to other channels.
