Yamaha P-150 Boot up problem

Synth Repair
1

Hi All
New user from Switzerland here. I’ve just bought a secondhand Yamaha P-150 piano for my daughter to start learning. I know, it’s old, very old, 1995 to be precise. It has one problem, that you have to press the power switch several times before it switches on. When it does come on, it plays perfectly. I managed to find circuit diagrams for other newer models which still use the MA60 PSU and power amplifier board. I’ve done several checks and I believe the correct voltages are present at the connectors leaving the MA60 board each time I switch it on. When it doesn’t boot up, the LCD backlight comes on but there is no text on the display and the loudspeaker muting relay doesn’t click on. I suspect the problem may be on the motherboard ‘DM’ but I don’t have a schematic diagram for this. My question is two-fold:

  1. Are there any known problems with the MA60 power supply board that I need to address?

  2. Can anyone give me a pointer on how I might find a circuit diagram for the ‘DM’ motherboard?

I’d be most grateful for any advice.
Thanks

Dino

2

Hi Dino,

There is an official distributor for service manuals authorized by yamaha germany: Schaltungsdienst Lange in Berlin.
https://sdl-online.de/dokumentationen/
They sell the service manuals. They sell copies, not originals, but the quality is very good.

And regarding your problem: I am quite sure, that the circuit for the powerup-reset acts too fast. This ciruit is usually a simple ‘unload a capacitor and send a reset when the capacitor is loaded fully again’. If the capacitor degrades, the load time will be faster, so the reset comes too early. A very simple test is to add a momentary switch, which shortens this cap.

3

Hi Florian
Many thanks for your reply, that’s really useful. I’ll try the company you mentioned to get the service manual. I’m also sure you’re right about the reset circuitry and old capacitors.
I’ll report back when I have made progress.
Regards

Dino

4

Hi Florian
I have to say I am very pleased with the service I received from Schaltungsdienst Lange in Berlin as per your link. The service manual arrived within 5 days. I identified the power up capacitor and added a reset switch as you suggested.
The piano restarts reliably every time I press the reset switch.
I just have to wait for my replacement capacitor(s) to arrive before I can complete my repair.

1 Like
5

And I’m pleased to report that replacing the capacitor in the reset circuitry has indeed fixed the problem. Thanks to @fanwander for the tip.

1 Like
6

Hi Dino

Did you find out what was wrong? because I have exactly the same problem with my P-150 :slight_smile:

7

Hi there
Yes, I solved the problem. On the main CPU board there is a reset circuit, it’s just a resistor and capacitor that together form a time constant that holds the CPU reset pin low and slowly releases it. The idea is that the CPU is held in its reset state until the power supply has switched on and all the voltages have stabilised. The capacitor in my reset circuit was broken. I replaced it with a new capacitor and now everything works fine.
From memory I can’t remember which capacitor it was, but if you need help finding it, let me know and I’ll find my notes from 2 years ago.
Good luck!

Dino