Followup: Success ... replacing C404 solved the problem. I reinserted all 76 screws and it still works.
Thanks again everyone for your advice and support!

Hello

@MrChips, many thanks for that offer. The service manual is mostly the same as the P85, and can be found here. The relevant schematic is on the next-to-last page.

I actually have a digital IR thermal sensor that I can use, and could power up the board, short PSWON to ground to enable +12V, and then poke around with the gun to see if I can find a particularly hot location. It seems most likely that C404 or the regulator itself is shorted (IC401), since even my crude ohmmeter gives slightly lower reading in that area. Other than those and C405, I don't see any other components that take +5D and ground.

Tentative plan: I can probably lift out C404 without too much trouble, though the regulator is another story since it is bolted to a heat sink and hard to access. However, after removing C404, if the short remains, I can clip the output of the voltage regulator to see if that fixes the short. If not, I can run a wire to repair it, although that will mean that I struck out). C405 is under that massive heat sink.

Here is a photo of the area:
View attachment 240340

Hello 1 have an yamaha P95 without function no sound, no led i have read :is this corectly to start the power supply AM Bord without any another board i must connect pswon permanently from the kathode D402 to ground? what is the function for pswcnt?
I have only 12V on the emitor from TR401, can anybody help me?
i found C112 with short an replaced it but without success

Moderator edit: New thread created from this.

 

Welcome to AAC!

Do you have a schematic for the P95? None of the other references to this model have been able to find a schematic.

 

@fritzfritz

Yes, to try to "turn on" the AM board, you have to ground PSWON, the cathode on D402. I believe the function of PSWCNT is to continue to pull down on the base of TR401, for when you release the power button. In other words, when you press the power button, it activates the power regulators, which in turn starts the CPU, which then brings PSWCNT high to activate TR402, so that when you take your finger off the power button, the power stays on instead of simply turning off.

When I was doing my debugging (with the power LED not even turning on), I just ignored PSWCNT completely.

Is the +12 rail shorted to ground, on the collector side of TR401? I forget where the best place to measure it is; I think I used the positive side of C406, C407, C410, or C411. Or maybe it's shorted to ground on the output side of the +5 regulators, C404/405 or C408/409?

Do you have the P85 schematics to work off of?

 

@fritzfritz

Yes, to try to "turn on" the AM board, you have to ground PSWON, the cathode on D402. I believe the function of PSWCNT is to continue to pull down on the base of TR401, for when you release the power button. In other words, when you press the power button, it activates the power regulators, which in turn starts the CPU, which then brings PSWCNT high to activate TR402, so that when you take your finger off the power button, the power stays on instead of simply turning off.

When I was doing my debugging (with the power LED not even turning on), I just ignored PSWCNT completely.

Is the +12 rail shorted to ground, on the collector side of TR401? I forget where the best place to measure it is; I think I used the positive side of C406, C407, C410, or C411. Or maybe it's shorted to ground on the output side of the +5 regulators, C404/405 or C408/409?

Do you have the P85 schematics to work off of?

I have the schematics from the P85, i have check all capacitor for short, i found only one with short : C112, but i dont now if the another capacitor are OK, i order TR401 to replace it

 

So are you saying that the emitter of TR401 is +12V, but there is no +12V on the collector of TR401 even when PSWON is pulled low? And that when power is off and capacitors are discharged, there is no short circuit between the collector of TR401 and ground?

 

So are you saying that the emitter of TR401 is +12V, but there is no +12V on the collector of TR401 even when PSWON is pulled low? And that when power is off and capacitors are discharged, there is no short circuit between the collector of TR401 and ground?

I have take it out TR401 in the multimeter i have the value 11 in the pnp socket , but i have the same value in the npn socket with the same transistor, i wait now for my order with a new 2SB1342 to instal a new one

 

I have take it out TR401 in the multimeter i have the value 11 in the pnp socket , but i have the same value in the npn socket with the same transistor, i wait now for my order with a new 2SB1342 to instal a new one

Today i install the new transistor TR401 an now i have 5 Volt on theoutput from the regulator IC401 but only 0,2V on the output from the IC 402, so i deinstall and connected to the input 12V on the output i dont have the 5 Volt i orderd a new IC402 AN78N05 regulator, so i have the newer ending story with this power supply, i come back when i become the new package

 

I am interested to know how you discovered that C112 was shorting. There are too many other components in parallel with this so that diagnosing this would be very difficult for even the most experienced technician.

 

I am interested to know how you discovered that C112 was shorting. There are too many other components in parallel with this so that diagnosing this would be very difficult for even the most experienced technician.

i measure with the ohmmeter and have detected the short , the i deinstalled out from the power supply an measured again and i have 0 Ohm

 

i measure with the ohmmeter and have detected the short , the i deinstalled out from the power supply an measured again and i have 0 Ohm

I understand that but how were you able to single out C112 as being the reason for the short when there are many other components connected in parallel across +3.3D and GND?

 

I understand that but how were you able to single out C112 as being the reason for the short when there are many other components connected in parallel across +3.3D and GND?

I applied the ohmmeter to the capacitor and my multimeter beeped and since the electrolytic capacitors die over time I unsoldered it and my multimeter always beeped, which I don't understand what this capacitor has broken, the transistor and the voltage converter to 5 volts I have found so far

 

I applied the ohmmeter to the capacitor and my multimeter beeped and since the electrolytic capacitors die over time I unsoldered it and my multimeter always beeped, which I don't understand what this capacitor has broken, the transistor and the voltage converter to 5 volts I have found so far

new IC402 AN78N05 is arrived an i soldered in on the AM Board i have check the voltage on the output and i have 5 Volt on punkt +5 A ond +5D so reconnected to the DM Board on the piano the power led turm on but turn off when i thake out the finger,so i shorted pwson to ground and the IC402 was very hot, i disconnected from the DM board and check the 5v are all fine, but the piano didn make any sound , only with the AM Board and the shorted pwson i check on the connector CN101 to the DM Board on pin 6 14 and 16 +5V is OK
The IC402 will only get hot with conected AM Board an shorted pwson, i think i have an isue on the AM board becouse the board doesnt remain on or is the isue in area TR402 ?

 

I think if the issue was just TR402 then the piano would work (make sounds) if you kept your finger on the Power button, or pulled down on PSWON. So unless it's making sounds when the LED is on, there are other problems that are causing the CPU to not operate.

I am not sure how you measured the voltages on CN101. Did you do this with the AM connected to DM? With the DM board disconnected and all power off, what is the resistance to ground on +5A and +5D (measured on the DM board)? It sounds like there might have a short to ground on the DM board. If IC402 is overheating, of course you would suspect +5A. Although it wouldn't surprise me if IC402 would get hot even when it is working properly.

If there is no obvious short circuit on +5A and +5D on the DM board, it would be interesting to know what the voltages on the DM board, when the boards are all connected and the power button is pressed. Although I would try to leave it in that condition for as short a time as possible, so you don't cause more damage.

 

I think if the issue was just TR402 then the piano would work (make sounds) if you kept your finger on the Power button, or pulled down on PSWON. So unless it's making sounds when the LED is on, there are other problems that are causing the CPU to not operate.

I am not sure how you measured the voltages on CN101. Did you do this with the AM connected to DM? With the DM board disconnected and all power off, what is the resistance to ground on +5A and +5D (measured on the DM board)? It sounds like there might have a short to ground on the DM board. If IC402 is overheating, of course you would suspect +5A. Although it wouldn't surprise me if IC402 would get hot even when it is working properly.

If there is no obvious short circuit on +5A and +5D on the DM board, it would be interesting to know what the voltages on the DM board, when the boards are all connected and the power button is pressed. Although I would try to leave it in that condition for as short a time as possible, so you don't cause more damage.

the voltages on CN101 Connector was measured without DM Board i try to measured the resistance on the DM Board for +5A and+5D pin

 

the voltages on CN101 Connector was measured without DM Board i try to measured the resistance on the DM Board for +5A and+5D pin

the measured pins on CN101 Connector

without connected DM
Pin6 420 Ohm
Pin18 473 Ohm

with connected DM
Pin6 493 Ohm
Pin18 73 Ohm

thanks for your support but i think when the problem is on the DM Board i cannot do anythink because the SMD layyout is very small an i dont have thr right tools

 

the measured pins on CN101 Connector

without connected DM
Pin6 420 Ohm
Pin18 473 Ohm

with connected DM
Pin6 493 Ohm
Pin18 73 Ohm

thanks for your support but i think when the problem is on the DM Board i cannot do anythink because the SMD layyout is very small an i dont have thr right tools

Now i have measured the voltage on CN101 Connector

with connected DM Board an the finger on the Powerbutton
Pin6 3,2V
Pin18 5V

without DM board and short PWSON

Pin6 5V
Pin18 5V

looks like the DM Board pulls to much current an i need an replacement DM Board

 

Yes, it does appear to be the DM board then, since +5A is too low.

Maybe I'm looking at the schematics wrong, but it seems strange that a +5A problem would cause the CPU to not operate. It appears that the CPU is driven by +5D and other voltages derived from +5D, so I would expect the power to stay on when you take your finger off the button. But anyway, it's good that the power goes off, since that could prevent damage.

If I search the Internet for Yamaha P85 DM, I see one for $152 USD, but I don't know if the P85 DM will work in the P95, and there is still a possibility that it's not actually the DM board that's the problem.

Sorry I don't have any other suggestions. :-(

 

Now i have measured the voltage on CN101 Connector

with connected DM Board an the finger on the Powerbutton
Pin6 3,2V
Pin18 5V

without DM board and short PWSON

Pin6 5V
Pin18 5V

looks like the DM Board pulls to much current an i need an replacement DM Board

i have check the DM Board for short circuit
i found the C518 with 75 Ohm and the 3,3V Regulator IC501 (BA33PC0FP ) with short between Pin 3(out) and Fin (ground)
i think the IC501 Regulator is the Problem with the short he damaged on the AM Board the 5 Volt Regulator

 

The weird thing about that is that IC501 is supplied by +5D, yet the low voltage was measured on +5A, and the damaged voltage regulator on the AM board sourced +5A.

So while there may indeed be a problem with IC501 (or perhaps a capacitor on its output, like C510), I don't understand how that would explain the +5A problem. I wonder if this keyboard was hit with a power surge, since now it appears that you've found at least 3 bad components.

 

The weird thing about that is that IC501 is supplied by +5D, yet the low voltage was measured on +5A, and the damaged voltage regulator on the AM board sourced +5A.

So while there may indeed be a problem with IC501 (or perhaps a capacitor on its output, like C510), I don't understand how that would explain the +5A problem. I wonder if this keyboard was hit with a power surge, since now it appears that you've found at least 3 bad components.

i buy this keyboard as defectiv with (no Power no sound) i dont know the history, i have seen only the cable under the DM Board was connected crooked, but on the boards i have not seen desoldering it was all original, maybe the predecessor has connected a external powersupply with + and - reversed