WX5 Voltage Margin Experiment
At the suggestion of Guy Zumpetta.... Tonight I investigated the WX5 "blinking LED" problem that some windlisters noticed when using their WX5 with a BT7. We already had a strong clue on the nature of the problem when a Yamaha tech fixed a windlister's problem by replacing the 8V regulator in the BT7 with a 9V regulator. That implied the WX5 wanted to see something bigger than 8V on the WX-phantom power line (the mini-DIN connector).
The "blinking LED" condition occurs on Steve's WX5 whenever the WX-phantom power drops below 7.4 volts. Even if the voltage subsequently rises above 7.4V, the LEDs continue to blink.
Using my homebrew BT7, I am able to apply any external voltage to the WX5 via the coaxial power jack I installed for when I did not want to run on a 9V battery. To this I connected my adjustable DC power supply. Starting at my nominal 9V, I gradually decreased the WX-phantom voltage in 0.1V increments until the LEDs started to blink. Perodically, I would play the WX to ensure I was simulating normal conditions - in case playing caused momentary dips in my power source. At 7.4V the LEDs started to blink. I proceeded down to 6.5V with no change. I did not venture below 6.5V for fear of blowing up Steve's WX5! I repeated this several times to verify the 7.4V threshold. Once the LEDs were blinking, I was able to turn up the WX-phantom voltage to as high as 10V with no stopping the LEDs from blinking. It would seem that the electronics inside the WX5 latch the low voltage condition signal. The condition will reset if you turn the WX5 off, then on again, either by it's built-in power switch, or via the power source.
So what's this mean for the average user: Not much.
- If you have a BT7, indeed changing the 8V regulator to 9V will be an excellent fix.
- If you use a VL70m or MFC10 with built-in WX connector, you just need to be aware of the problem. I haven't looked at VM70m or MFC10 schematics yet, though we haven't heard of any problems yet.
- If you modify your own gear to supply power from inside a synth (such as putting WX-phantom power on the unused DIN pins), then you should review what phantom voltage you send and consider using a nominal 9V.
- If you use a 9V battery and/or wall wart with Aaron's schematic, you need do nothing.
Again my thanks to Steve for allowing me to teste his WX5 for a few weeks before I send it off to him! Thanks to Guy for the idea of the voltage margin test in the first place. This test continues the tradition I started waaay back when I was a newbie on the windlist and I was powering my WX11 and WT11 from car assy sockets and 8x D-batteries. I think the WT11 voltage margin test and subsequent battery box was my first WX hack!!