Yamaha P71B – Powering on, but no sound from speakers or headphones.
I’ve got a Yamaha P71 that powers on but produces no sound through the speakers or the headphone jack.
I’ve tested the power supply with a multimeter, reading ~12V so that’s fine.
I checked the DM Board test point 1, which should read 12V, however I got a reading of ~4V
Luckily I managed to get a hold of a service manual and it says with that result there are potential faults in the JK board (2nd pic) which could be the fuse, diode or MOSFET.
I tested the fuse with my multimeter in continuity mode and it is OK. I’m unsure about how to rule the diode out, do I remove that for a more accurate reading too? I’m going to remove the MOSFET tomorrow to test outside of the board since my research online said to do that.
Any and all suggestions, or inquiries are welcome! Thank you for reading.
*edit Removed post guides haha
Nothing stands out, but look at the two transistors TR101 and the big one beside it.
trying to find a schematic for it led me to a malware attack.
This is from the service manual. Hopefully this helps visually.
It’s also worth noting I tested the keybed via MIDI and everything checked out fine there.
After removing the MOSFET FT101 and testing with a multimeter it gave normal readings.
I also removed the transistor TR101 and it was not giving normal readings.
I’m going to try and source another transistor and see if that solves the issue.
if you did the midi test, then its probable on the other board.
The only part that stands out is TR102, just to the lower left of the top center 100uf 25V electrolytic capacitor.
it has two small dots that could mean its blown, or a dirt mark. have a look under a microscope, or some other zoom.
other than that, its test every component. I think Syntaur has a replacement board but were not there yet.
there’s also powering the circuit and looking at it through a thermal camera if you have one. The hottest or coldest part is usually the culprit.
So I’m going to admit to my mistakes in this next reply.
I got some replacement TR101 in the mail and installed it backwards (I flipped it the correct way now but I had powered the keyboard once with it reversed…), and now the board is powering on as soon as the power adapter is plugged into the piano. There is still no sound from the board.
After correcting the orientation of TR101, I tried a standard factory reset by holding C8 while introducing power and the power led blinks like it’s going through it’s reset but still no sound.
I’m able to power off the keyboard after plugging the adapter in, but I can’t power it back on afterwards, maybe there’s something there…
I tested voltages on the DM test points and they seem to be accurate now so that’s a plus I guess.
The next step is find where the audio signal isn’t. Follow the audio signal using the schematic from the audio output back to where it originates, and see where the audio signal should be but isn’t, and that should be the problem part.
I double checked the power switch with my multimeter and that isn’t the issue. I revisited the service manual and it said to check FZ101 TF101 and D101. The diode is good, removed it from the board to test, and the fuse has continuity. MOSFET FT101 I found was giving a very low reading so I’m going to order that and see what happens in about a week’s time. Will provide an update when I get that part.
