How can I diagnose why isn't it powering on so I can try to fix it?

Hi @jotitax ,

The current supply value doesn’t matter as the device will only draw as much current as it requires.

What does matter is the value and the polarity of the DC voltage supply.

Looking at the specifications for the RP-70, it requires a 9.6V DC 300mA -ve power supply from the adapter and not the usual +ve power supply that it found on most adapters i.e. -ve is on the centre pin and not +ve, it is reversed to what is the usual case.

Most probably the more common 9V DC +ve power supply adapter was used. The voltage difference in this case is only negligible and wouldn’t affect performance too greatly and wouldn’t damage the device. It is the polarity of the voltage supply that was the problem. Most likely the device doesn’t have reverse input voltage polarity protection so therefore the damage occurred.

Here’s a composite image of some generic DC adapters to show what to look for on the adapter to know what the polarity of the DC power supply is. Usually the polarity symbol is also shown on the device itself to help to know what the polarity of the supply voltage should be, especially in this case where it is reversed to the norm. Some adapters even come with reversible plugs as opposed to fixed plugs, so that the polarity of the supply can be changed to suit if required, so you have to be aware of this when using them.

(click on image to enlarge for better viewing)

You will have to open the device and check for damaged components close to the power supply input.

I can’t find a schematic for the device but if you can’t see anything obvious, post some close up images of the board back here

Here’s how to do this. 在已经存在的问题里加入图片

Here’s a link to the ifixit DigiTech RP70 guides, that will help to open the device so that it can be inspected, if you haven’t already done so.