I am a Japanese Everdrive user.
I am sincerely grateful for the wonderful update!
Correspondence to the extended sound source is really wonderful.
I am one person who thinks of V20 IO error problem, voltage is the cause.
I am glad that the case I experienced is helpful for something.
[Actual machine activation status]
First of all, I tried to start Everdrive with portable compatible machine 1 (FC-Portable, battery-driven), but it did not start. However, when the power was turned on for about 10 minutes, the menu was activated. Therefore, I started the portable compatible machine 1 with the AC adapter. The activation rate is 90%. However, IO errors occur frequently in menu move, selection, ROM loading.
Next, I tried to start up Everdrive with a portable compatible machine 2 (pokeFAMI LIGHT, battery-powered), but it did not start up again. Likewise, if you turn on the power for about 10 minutes, the menu will gradually start up.
Nothing is displayed → OS Init → IO Error / 52 → Error 10 → Action!
IO errors also occur frequently afterwards.
Of course, Famicom and Twin Famicom will start 100%.
I do not have a new NES.
[Voltage measurement]
Since there is a significant difference in the starting condition, the voltage between GND - VCC (+ 5V) was measured and it became as follows.
1 Startup rate 100%
Twin-Famicom · · · 5.05 V
2 Boot rate 90%
Portable compatible machine 1 AC adapter drive · · · 4.4 V
3 Boot rate 0% to 50% (After turning on the power for over 10 minutes)
Mobile compatible machine 1 Battery operated · · · 3.8 V
Mobile compatible machine 2 Battery operated ··· 3.8 V
Obviously there seems to be a start-up difference with voltage!
[Modification]
My favorite is to operate Everdrive with a portable compatible machine 2 and to enjoy a wonderful expanded sound source, so I modified the portable compatible machine 2.
It is a remodeling that makes GND-VCC (+ 5V) closer to one with a startup rate of 100%.
By the way, I have little knowledge about electronic circuits.
The portable compatible machine 2 has a built-in voltage regulator circuit, and the place where the regulated power supply is currently set at 3.8 V is changed to 5 V in voltage.
[result]
With portable compatible machine 2, Everdrive has started to operate steadily!