Digital electronics troubleshooting guide/book

[WakeUpWolfgang]

I do some digital electronics troubleshooting but some times I have to have someone else finish it. Anyone know any good book or guides for troubleshooting digital electronics? I test voltages but I really don't know what to do past the power supplies.

[WakeUpWolfgang]

I know how they work I took some classes at college but we did not design or troubleshoot. I have designed some projects and still making some. What is hard for me is trying to figure out other peoples work. What I am doing at work when fixing electronics is similar to a motherboard in a computer. (DVRs for CCTV systems and AMPS for sound systems) Most of the companies will give out the schematics so I can fix them but its the DVRs that I have problems.