Yamaha P95 no power

Thread Starter

HowMe

Joined Apr 17, 2021
10
I've read all the posts about no sound from a Yamaha P95 (or P85), but everyone seems to at least have power working.

I came across a P95 that had been left plugged straight into a wall socket for over a year. Pressing the Power button results in ... nothing. I checked the AC adapter with a voltmeter and it seemed fine. Has anyone encountered this particular problem before with a P85 or P95? I'm assuming it was caused by a power surge, but that's a pure guess.
 

Thread Starter

HowMe

Joined Apr 17, 2021
10
Thanks for the replies...I don't actually have the keyboard here to test at the moment, but will follow up when I do so. Judging from the general schematics in the P85 manual, the problem may not be as easy to isolate as I'd hoped, since the LEDs are sourced by the CPU and not simply from a power rail. But I will poke around and see what I find.
 

Thread Starter

HowMe

Joined Apr 17, 2021
10
Update: I received the P95 and poked around. Looks like there is a dead short from +5D to ground on the AM circuit board. I removed the board completely and inspected both top and bottom, but was unable to see anything obvious. So now I am left with trying to locate a short.

All I have is a basic multimeter, with resolution to 0.1 ohms, so not great. I might try using an ancient Sony camcorder that is supposed to have an IR night mode, to see if I can identify any hot spots. I'd hate to invest a lot of money into more equipment if I don't have to, though. I might try removing some jumpers to see if that helps me isolate the fault.
 

Thread Starter

HowMe

Joined Apr 17, 2021
10
@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:
area.jpg
 

MrChips

Joined Oct 2, 2009
24,175
Thanks for the P85 Service Manual.
Don’t remove any components yet. Use your DMM and look for 12V and 5V.
Give me some time to look at the schematics.
 

Thread Starter

HowMe

Joined Apr 17, 2021
10
Thanks for the P85 Service Manual.
Don’t remove any components yet. Use your DMM and look for 12V and 5V.
Give me some time to look at the schematics.
Thank you! +12V and +5A are fine. But +5D was less than 1V, and is shorted to ground.
 

sagor

Joined Mar 10, 2019
479
IC401 (5V regulator) also feeds other regulators on other boards. If the dead short is with the IC401 board removed, then it could be the C404 capacitor or the 5V regulator itself.
If the output of IC401 is connected to other things on other boards, it could be one of many other devices that are shorting out the +5D.
 

Thread Starter

HowMe

Joined Apr 17, 2021
10
It was indeed C404. I removed it and now need to find a replacement 100μF/16V low ESR cap.

Is there a source that you folks typically use? I see some on Amazon but with a long lead time. I thought of scavenging from C216 or C217 from the same board, since those seem to be just for the headphones, but I'd like to repair it fully if I can.

Thanks for all your help!
 

MrChips

Joined Oct 2, 2009
24,175
I could pop a couple in the mail for you but the cost of postage would be more than the price if you can find it locally.
Maybe another member closer to you can help out. State your city, state.
 

Thread Starter

HowMe

Joined Apr 17, 2021
10
I could pop a couple in the mail for you but the cost of postage would be more than the price if you can find it locally.
Maybe another member closer to you can help out. State your city, state.
I'm in Framingham, Massachusetts. BTW, these are radial, with about 5mm lead spacing, low ESR.
 

Thread Starter

HowMe

Joined Apr 17, 2021
10
I guess unless I hear from someone soon, I'll just order some of these from Digikey tomorrow - They seem to be similar in spec, and I can get 10 of them for about $7.50 including shipping. Thanks; I will let you know how it turns out.
 

Thread Starter

HowMe

Joined Apr 17, 2021
10
Followup: Success ... replacing C404 solved the problem. I reinserted all 76 screws and it still works. :cool:
Thanks again everyone for your advice and support!
 
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