Hi
I bought this keyboard on a garage sale. The seller told me that the power button is bad, one has to push the button several times to make the keyboard power on. Thinking it was an easy fix I bought it. After sitting on a shelf for a year a decided to take a look at it, since it would not come on anymore. The switch turned out to be OK. It is working as designed. The keyboard is powered with 9V from the batteries or 12VDC from external power adapter. The stereo amp is powered by the 9-12V and is working. The power is feed to the main board, to two 5V regulators which power two microprocessors and the rest of the circuitry. The main processor is an old CMOS 8 Bit uPD78213 (NEC). The supporting processor is even older Hitachi HD63B05 and is used for Keyboard switch matrix. Both processors are supplied with 5V. However, the main processor 12 MHz oscillator seems to be not working correctly. I could measure only 0.5Vpp with the oscilloscope probe. Shouldn't be there at least 4-4.5Vpp? A 3 digit LED display is connected to the main processor which is dead. Did anybody had a similar problem w a Yamaha Keyboard? Any hints will be greatly appreciated. Thank you.

 

Let's start with the model number of the Yamaha keyboard, shall we?

 

Sorry. It is a PSR310. I searched the internet and it seems that this was a common problem but no solution was published.

 

Chances are the oscillator is a quartz crystal connected to the processor chip.
You need to probe elsewhere to find a clock signal.

Find the circuit schematic if you want to make some headway.

 

I did find a schematic on the net (attached). There are 3 processors that have their own ceramic resonators w. different frequencies. The main processor has a 12 Mhz resonator. I probed most of the pins of IC1 with oscilloscope. No signal whatsoever, nothing except +5V, Gnd and the faint oscillator signal. All chips are cold to the touch even when powered for an hour. I don't know where to start. I am an analog guy.

 

Use your oscilloscope probe and look for activity on the address and data bus of IC1 CPU.
Measure the voltage on RESET signal, IC14-1 and IC1-14.

 

No activity on address and data bus. LED display dead. Reset signal is low (0.3V) even when I removed IC-14. I don't see a pull-up resistor anywhere.

 

/RESET originates at IC14 and is used in various places.

Something is pulling it LOW. Either IC14 is bad or you have to trace through the schematic drawing and find everything that is connect to /RESET.
/RESET must be HIGH (5V) for the system to run.

 

Correction. Reset signal is high, 4.36V if that is a valid high. I forgot to properly ground my probe. But still no activity on data or address lines.

 

Probe the signals on IC6 ROM.
Look for changing signals (0 to 5V) on any of the address lines (e.g. pins 1-10) and data lines (pins 11-19)
and especially CE/ pin-22 and OE/ pin-24.

 

MrChip, on IC6 I measured the following:
pin1 = 5VDC
pin2>4 = no signal or DC
pin5>12 = square wave 2.5Vpp increasing frequency
pin13>15 = mixed signal 3.5Vpp
pin16 = 0V DC
pin17>21 = square wave 3.5Vpp
pin22 = 3.6VDC
pin23>27 = square wave 4.8Vpp
pin28>29 = 5mV DC
pin30>32 = 5VDC
Thank you for your help so far. Merry Christmas.

 

Without carefully studying your posted results, it would appear that IC1 CPU is up and running and the problem is not quite obvious at this point.

 

I did some further testing. For some reason there is now activity on almost all chips except IC1 MPU. Display is dead, all push buttons are dead, keyboard scanner dead, not one LED lit.
There is no clock signal on pin 46, nothing. At this point, I think the MPU is toast.