Yamaha P105 digital piano - no standby / no power

[beetle1303]

Hi,
I received this Yamaha P105 digital piano completed dead - no power and no standby lights. Pressing the power button does nothing.
I have checked the power adapter has 15V output to the piano. I opened up the keyboard, and did some basic checks, and there is 15V input to the power supply board. But that is apparently no power feed into the main board that connects to the power switch button.

Attached is the pictures of the PCBs, and the service manual I downloaded.

I need help to get guide me where to start tracing for problem(s).
Thank you.

[petehall347]

Re: Yamaha P105 digital piano - no standby / no power

i take it power comes in on the left side by TH1 ?
os that a regulator lower left ?

[budm]

Re: Yamaha P105 digital piano - no standby / no power

What DCV do you have at A, B, C, D, E, F, and G with ref to the circuit ground point when Power switch is OFF and when Power switch is ON?
What is the resistance reading of the Polyfuse TH1?
See attached picture.

[beetle1303]

Re: Yamaha P105 digital piano - no standby / no power

i take it power comes in on the left side by TH1 ?
os that a regulator lower left ?

Yes, power comes in by TH1, and yes that is a TR2 - TJ20A10M3.

[beetle1303]

Re: Yamaha P105 digital piano - no standby / no power

What DCV do you have at A, B, C, D, E, F, and G with ref to the circuit ground point when Power switch is OFF and when Power switch is ON?
What is the resistance reading of the Polyfuse TH1?
See attached picture.

The DCV readings (to be sure I marked on the board the points where I took the reading):
Power on at the wall socket:
A = 16.64V
B = 0V
C = 0.33V
D = 0V
E = 0.06V
F = 0V
G = 16.64V

Pressed the power button on the keyboard:
A = 16.64V
B = 0V
C = 0.33V
D = 0V
E = 0.06V
F = 0V
G = 16.64V

**Note that the power button led is never on - no standby light, no power on light.

The resistance reading of TH1 = 0.07ohm.

[budm]

Re: Yamaha P105 digital piano - no standby / no power

The DCV readings (to be sure I marked on the board the points where I took the reading):
Power on at the wall socket:
A = 16.64V
B = 0V
C = 0.33V
D = 0V
E = 0.06V
F = 0V
G = 16.64V

Pressed the power button on the keyboard:
A = 16.64V
B = 0V
C = 0.33V
D = 0V
E = 0.06V
F = 0V
G = 16.64V

**Note that the power button led is never on - no standby light, no power on light.

The resistance reading of TH1 = 0.07ohm.

OK, the MOSFET is not being turned on.

Point 'E' should have about 16V when power switch is not push.

Check diode D501, D502, R503 (12K).

We also need to verify if the power switch is OK or not.
Remove power from the unit, set Ohm meter to 20 or 200 Ohm scale, Black probe on the Circuit ground, Red probe on test point 'E' (PWSW), then push the power switch (it is a momentary type switch), you should see low resistance reading when you push it and high resistance when the switch is released..

BTW, the test done in your post #5, all the boards and cables are in place, correct?

[beetle1303]

Re: Yamaha P105 digital piano - no standby / no power

OK, the MOSFET is not being turned on.

Point 'E' should have about 16V when power switch is not push.

Check diode D501, D502, R503 (12K).

We also need to verify if the power switch is OK or not.
Remove power from the unit, set Ohm meter to 20 or 200 Ohm scale, Black probe on the Circuit ground, Red probe on test point 'E' (PWSW), then push the power switch (it is a momentary type switch), you should see low resistance reading when you push it and high resistance when the switch is released..

BTW, the test done in your post #5, all the boards and cables are in place, correct?

Black probe on circuit ground, red probe on point E:
Power button not pressed: 80-90Mohm
Power button pressed: ~3ohm

D501 (D15?): 750ohm, reversed probes: open
D502 (D13?): 750ohm, reversed probes: open
R503 (R26?): 11.96Kohm

Tests done with all boards and cables connected - except the cable to the keyboard is removed from mainboard.

[budm]

Re: Yamaha P105 digital piano - no standby / no power

So the component designators of the schematic do not match the PCB designator, this will make it a little more complicated to troubleshoot.

As you can see, the Voltage should be at 'E' where it is connected to the Power Switch (I look through the schematics top find out how the Power Switch is connected), you may what to check the path from point 'E' back to the Gate of the P-CH MOSFET to see why you are not getting Voltage at all on point 'E' when Power switch is not pushed. There is not much just resistors and diode.
When you press the Power Switch, it brings the Gate Voltage down toward ground so the G-S Voltage is more than 3V to turn on the MOSFET, when MOSFET is off, the Voltage on the Gate and Source will be the same.

[beetle1303]

Re: Yamaha P105 digital piano - no standby / no power

So the component designators of the schematic do not match the PCB designator, this will make it a little more complicated to troubleshoot.

As you can see, the Voltage should be at 'E' where it is connected to the Power Switch (I look through the schematics top find out how the Power Switch is connected), you may what to check the path from point 'E' back to the Gate of the P-CH MOSFET to see why you are not getting Voltage at all on point 'E' when Power switch is not pushed. There is not much just resistors and diode.
When you press the Power Switch, it brings the Gate Voltage down toward ground so the G-S Voltage is more than 3V to turn on the MOSFET, when MOSFET is off, the Voltage on the Gate and Source will be the same.

BUDM - You are a Magician!! A BIG THANK YOU

I traced from point 'E' to D15 - and Bingo, the broken spot right at the centre of this path. I jumped the path, and yes, there is light!!

Power on at the wall socket:
A = 16.64V
B = 0V
C = 0.46V
D = 0V
E = 15.58V
F = 0V
G = 16.64V

Pressed the power button on the keyboard:
A = 14.78V
B = 0V
C = 14.98V
D = 3.25V
E = 3.18V
F = 3.18V
G = 0.99V

Now, a simpler question on how best to mend the broken path - easy way is just jumper up the 2 end points? Or is there a safe way to patch the broken path?

[budm]

Re: Yamaha P105 digital piano - no standby / no power

Great news.
Just use small wire connected to the solder pad of each end of the broken trace on the bottom side of the board, then hot glue the wire down to the board.
So is the trace broken due to hair crack on the circuit board? This type of material (paper base impregnated with phenolic resin) used for making PCB do not handle mechanical stress well, they tend to crack, not like FR4 glass epoxy PCB.

[beetle1303]

Re: Yamaha P105 digital piano - no standby / no power

Great news.
Just use small wire connected to the solder pad of each end of the broken trace on the bottom side of the board, then hot glue the wire down to the board.
So is the trace broken due to hair crack on the circuit board? This type of material (paper base impregnated with phenolic resin) used for making PCB do not handle mechanical stress well, they tend to crack, not like FR4 glass epoxy PCB.

Soldered a wire on each end of the trace, and put re-assembled everything back - the very delighted daughter, dis-believing I can repair it with help from Internet

Yes, it was a tiny bloated white dot along the path. I thought it was just a dirt/debris, and touch it DMM probe - it immediately "disintegrated" in tiny fragments and revealed the bigger spot that broke the path completely.

Thank you once again.

[krone]

Re: Yamaha P105 digital piano - no standby / no power

Hi forum,

My dad has brought to me a P105, it looks like its had coffee spilt on the power input board. I'm just checking the diodes because D9 looks a bit discoloured and D9 has forward voltage of 0.592V and a reverse voltage of 0.884, whereas all other diodes have only a forward voltage of 0.64V. D9 is also a bit discoloured and looks like it may have overheated.

I can't find D9 on the parts list, are all the diodes on this board the same value?

Thanks in advance,

Krone from Australia.

[krone]

Re: Yamaha P105 digital piano - no standby / no power

Hi forum,

My dad has brought to me a P105, it looks like its had coffee spilt on the power input board. I'm just checking the diodes because D9 looks a bit discoloured and D9 has forward voltage of 0.592V and a reverse voltage of 0.884, whereas all other diodes have only a forward voltage of 0.64V. D9 is also a bit discoloured and looks like it may have overheated.

I can't find D9 on the parts list, are all the diodes on this board the same value?

Thanks in advance,

Krone from Australia.

So after months on the shelf I have just managed to get this going again. The problem was shorted D9 and coffee on the PCB / keyboard diode circuit. thanks again =)

^_^

[stj]

can you backup any roms on it!