Received a good question from Andy P. today, asking about the current draw for the OLEDs keeping in mind the DX7 has a very old power supply.**
Here are some numbers I came up with for a limited, but representative, sampling of what I have on hand. These are actual current measurements, not voltage drop across diode measurements.
- Original non-backlit LCD … 1mA
- Yamaha’s updated backlit LCD … 24mA
- My drop-in replacement backlit LCDs … 18mA
- My drop-in replacement OLEDs … 21mA to 26mA
So I guess that the drop-in backlit LCDs save a little bit of power over the original and the OLEDs are about the same or maybe a few mA more. It should be noted that Yamaha offered the backlit kit for non-backlighted DX7’s for around $100USD back in the day. So I think we can conclude that the original DX7 had enough reserve current handling capacity for an additional 20-something mA at least.
** I haven’t had to rebuild any of these power supplies yet, but I have seen SXP90’s and DX7S’s that definitely stopped functioning due to power supply issues.
I also have a few of these for the SPX-90. I will check and see if they work in the TX81Z and MEP4 when I get a chance. These particular units use a funky “Yamaha special” LCD cable that is a PITA to recreate, but I have done so as true to the original.