hsiboy/Yamaha_SPX900-Repair_Notes.txt

## Yamaha_SPX900-Repair_Notes.txt
Yamaha SPx900 – repair log

-- FAULT --

Noted fault, "BATTERY LOW" warning on switch on, not passing audio.

Inspection revealed that a new battery was in place (reading 3.1v) and at some point, the 4 electrolytic capacitors on the PSU board had been replaced as well as the reservoir capacitor C163 across the 5v rail on the main board.

The display was very faint, and the LED backlight very dim. The display was original.

The replaced capacitors were all off brand.

The 3 voltage regulators (7805, 7915, 7815) had been mucked about with. Poor soldering, too much heatsink compound and the wrong screws in the heatsink.

-- REPAIR --

The battery monitor works by feeding the battery to an (obsolete) dual jfet opamp (into pin 3) via a 10Mohm resistor, this in turn feeds an ADC (IC213 pin1, which also reads external foot control volume).
The coin cell battery measured at 3.1V open circuit. Only one of the opamps in the 8 pin dip package is used.

Measuring the rails, the +/- 15v rail was missing.
Unlike the SPX90, this unit has a linear PSU. Two bridge rectifiers, 3 voltage regulators and 4 smoothing capacitors.
Replaced the 4 capacitors on the PSU board with Panasonic and Nipon-chemicon. Re-soldered the 3 voltage regulators.
Validated AC output from transformer secondary.
Validated +/- 15v and +5 lines.
Reconnected main PCB.

With the unit powered on, around 1.5v was present at pin3 of the battery monitor opamp IC210 and 3.2v at its output (pin 1).
The opamp needs +/- 15v rails. The "BATTERY LOW" warning was gone.

Replaced LCD display for a new one. The LED backlight was very dim and the contrast almost unreadable. Used a cheap Chinese display ($3 delivered), reused 14pin dip cable from old display.
The new display is 2mm narrower and doesn’t clip into the chassis like the old one.
Note: Pin 1 of the 14pin IDE is VSS. Display needs to derive backlight from 14 pin header.

On power on the mute relay could be heard clicking shortly thereafter. Expected behaviour.

Injecting audio into the input, the level meter LEDs illuminated as expected, however the output produced what sounded like a clock line. Fixed Square wave.
While inspecting the cause of this, plugs and switches were wiggled, and it was noted that the "program" display advanced. Successive wiggles advanced the program accordingly.
It was then noted that flexing the PCB near the right-hand side, caused the program to advance, the bypass LED to light and output audio was momentarily heard.

Put unit in self test.

Tests passing but noted an unresponsiveness to button pushes. Button test failed. Noted that some of the indicator LEDs were very dimly lit when they should be extinguished.
Removed the button PCB, found the black foam had become conductive. Removed with acetone.
Reinstalled PCB, buttons more responsive, but not reliable. Temporarily shorted buttons with jumpers, but still unresponsive, so while the buttons are old (and will be replaced) they are not the cause.
Replaced all buttons with 6x6x4.3 tactile SPST push button. Re-soldered all connections on board. It flexes badly when in use due to the construction. Same unresponsive buttons during test. Tested removed buttons out of circuit. Some worse than others. They needed replacing. This thing has clearly been operated by an 80Lb Gorilla.

Flexed main PCB again and noted behaviour, there is a broken track or dry joint somewhere. Checking visually with aid of microscope doesn’t reveal anything…

Begin arduous task of re whetting all the pins. Liberal flux application and lead based solder.

Found a lifted PCB pad under Yamaha flat package IC226 and several pins mid-air. Several Pins where adrift, possibly as the result of a previous reflow attempt.
This is the Yamaha YM6007 DSP II chip. Shouldn’t affect display etc, but would affect audio.
Not all pins need to be connected.
89,61,60,78,74,76,35,36 = NC

VDD pin 5,68
VSS pin 37,124

Bridged:
Pins:98,90,94
Pins: 96,97

Repairs made.

Power applied, display dead, system unresponsive. Clock sounding audio absent from output. Time to re-examine PCB. Some tracks are very fine.
Flexed PCB, got flickering on 7-SEG display.

Back to looking for short and or broken track.


Note: 5v current draw, 240mA
	Yamaha SPx900 – repair log

	-- FAULT --

	Noted fault, "BATTERY LOW" warning on switch on, not passing audio.

	Inspection revealed that a new battery was in place (reading 3.1v) and at some point, the 4 electrolytic capacitors on the PSU board had been replaced as well as the reservoir capacitor C163 across the 5v rail on the main board.

	The display was very faint, and the LED backlight very dim. The display was original.

	The replaced capacitors were all off brand.

	The 3 voltage regulators (7805, 7915, 7815) had been mucked about with. Poor soldering, too much heatsink compound and the wrong screws in the heatsink.

	-- REPAIR --

	The battery monitor works by feeding the battery to an (obsolete) dual jfet opamp (into pin 3) via a 10Mohm resistor, this in turn feeds an ADC (IC213 pin1, which also reads external foot control volume).
	The coin cell battery measured at 3.1V open circuit. Only one of the opamps in the 8 pin dip package is used.

	Measuring the rails, the +/- 15v rail was missing.
	Unlike the SPX90, this unit has a linear PSU. Two bridge rectifiers, 3 voltage regulators and 4 smoothing capacitors.
	Replaced the 4 capacitors on the PSU board with Panasonic and Nipon-chemicon. Re-soldered the 3 voltage regulators.
	Validated AC output from transformer secondary.
	Validated +/- 15v and +5 lines.
	Reconnected main PCB.

	With the unit powered on, around 1.5v was present at pin3 of the battery monitor opamp IC210 and 3.2v at its output (pin 1).
	The opamp needs +/- 15v rails. The "BATTERY LOW" warning was gone.

	Replaced LCD display for a new one. The LED backlight was very dim and the contrast almost unreadable. Used a cheap Chinese display ($3 delivered), reused 14pin dip cable from old display.
	The new display is 2mm narrower and doesn’t clip into the chassis like the old one.
	Note: Pin 1 of the 14pin IDE is VSS. Display needs to derive backlight from 14 pin header.

	On power on the mute relay could be heard clicking shortly thereafter. Expected behaviour.

	Injecting audio into the input, the level meter LEDs illuminated as expected, however the output produced what sounded like a clock line. Fixed Square wave.
	While inspecting the cause of this, plugs and switches were wiggled, and it was noted that the "program" display advanced. Successive wiggles advanced the program accordingly.
	It was then noted that flexing the PCB near the right-hand side, caused the program to advance, the bypass LED to light and output audio was momentarily heard.

	Put unit in self test.

	Tests passing but noted an unresponsiveness to button pushes. Button test failed. Noted that some of the indicator LEDs were very dimly lit when they should be extinguished.
	Removed the button PCB, found the black foam had become conductive. Removed with acetone.
	Reinstalled PCB, buttons more responsive, but not reliable. Temporarily shorted buttons with jumpers, but still unresponsive, so while the buttons are old (and will be replaced) they are not the cause.
	Replaced all buttons with 6x6x4.3 tactile SPST push button. Re-soldered all connections on board. It flexes badly when in use due to the construction. Same unresponsive buttons during test. Tested removed buttons out of circuit. Some worse than others. They needed replacing. This thing has clearly been operated by an 80Lb Gorilla.

	Flexed main PCB again and noted behaviour, there is a broken track or dry joint somewhere. Checking visually with aid of microscope doesn’t reveal anything…

	Begin arduous task of re whetting all the pins. Liberal flux application and lead based solder.

	Found a lifted PCB pad under Yamaha flat package IC226 and several pins mid-air. Several Pins where adrift, possibly as the result of a previous reflow attempt.
	This is the Yamaha YM6007 DSP II chip. Shouldn’t affect display etc, but would affect audio.
	Not all pins need to be connected.
	89,61,60,78,74,76,35,36 = NC

	VDD pin 5,68
	VSS pin 37,124

	Bridged:
	Pins:98,90,94
	Pins: 96,97

	Repairs made.

	Power applied, display dead, system unresponsive. Clock sounding audio absent from output. Time to re-examine PCB. Some tracks are very fine.
	Flexed PCB, got flickering on 7-SEG display.

	Back to looking for short and or broken track.


	Note: 5v current draw, 240mA