The products i will eventually atempt to fix will not have a diagram.I'm just learning how resistors,capacitors,and diodes work.For instance I'm trying to fix my alarm clock because only half of each number displays.But with out a diagram i dont know where to start.I dont know the voltage after the transformer etc so testing it has me clustered.i ordered a 300 in 1 electronic lab project kit i hope that gets me on track. i have a begenirs book I'm reading but these books Ive looked at and websites all teach what parts do.and to check them disconnected i can find anything that will give me an idea at where to start troubleshooting. ..... The DVD player had some kind of loose connection.i took it apart fiddled around with it for a few days because i was getting familiar with the parts and testing, and it worked. i had it apart and i disconnected the DVD disc so the laser wasn't on and i plugged it in. i was tapping on the voltage board i was originally playing with and shaking it while plugged in and the lcd screen stayed on ...didnt flicker on and off like it was before..that was the only board i took off and it stayed on.the other board I'm guessing was audio n video i didn't touch that but i think something is loose on the voltage board..any way thank u guys..im really motivated to learn this stuff again I'm a beginner so ignore how neuritic i might sound .. if u wanna talk about commercial or ressidential electrica lI know what I'm talking about.Hopefully IL learn this soon