Are you able to judge the safety of the repair? If not, contact someone who does or read up on the subject.
Some quick tips regarding safety:
If the device has an external power supply, and the voltage is less than 60 VDC or 25 VAC (can be found on supply), it is safe to touch with your hands.
For lower voltages, shorts can cause high currents which might still be dangerous.
Avoid metal jewelry since they can become dangerously hot if shorted.
2. Reproduce the problem before repairing
Sometimes the device is used the wrong way and not actually broken. Sometimes the issue even disappears during transport.
I which situations the problem occurs can say a lot. Note when the problem occurs, and when it doesn’t.
Consider when the problem started to further narrow down the search (e.g. use system indicators, such as LEDs or displays)
3. Search for repair solutions on the Internet
Check google for the specific problem. Keywords could include:
Manufacturer
Model type
Model name
Model’s product number
The issue you have
A diagnostic/error code, if there is one (LED blinking or an error code on a display)
If google didn’t bring it up already, check youtube. A lot of solutions get taped and land on youtube.
ifixit.com is a known homepage for repair guides, there is also a forum with an engaged community.
See on the manufacturers homepage if they offer service manuals or other guidance in case of a broken device.
4. Try the easy fixes first
Clean your device. Always a good opportunity. That applies both to hardware and software.
Are
all controls at the right settings? If you’re not sure, a lot of
devices offer a factory reset. This often removes personal settings or
even data, so consider backing up you device if that is possible.
Are there blown fuses?
Are all cables and connectors firmly seated?
Are there interlocked lids, and are they firmly closed?
Is power at all available to the device, either from cable or battery?