I actually have one thing on my workbench I find very useful when I have to troubleshoot a computer
I keep a CRT monitor on the side of the desk, and I have a DVI to VGA to make it easier to diagnose computers without moving my dual core HP I use for looking up service manuals and don't have to move it
Why CRT? I can find them cheap, so I use the cheapest I can get, yet does what I need it to do. Plus they are all over the place.... I have a spare CRT for bench work just in case
For HDD wiping, I keep a copy of DBAN in the HP I can use to wipe a computer out and be done with it
As to what I repair..... I will touch things very few people would fix on the component level, like power supplies..... DO NOT OPEN POWER SUPPLIES unless you know how to work in them! They are not toys, and they can bite pretty nasty!
Here's one example of a OEM PC I had to stop using for my main Linux PC, but I still have just in case.... my HP A400Y has 2 major issues on it..... HP uses a MSI motherboard in it, and I can tell, but they did 3 things
1) Killed OC on it(this is common on OEM systems so novices don't cook processors doing it if you OC, you need to get a better cooler to handle it)
2) No AGP slot when the 64MB onboard graphics are a JOKE and can barely handle Unity on Ubuntu Linux..... Intel onboard GPUs sucked back then, and it showed when you got a GPU for it
3) capped the CPU FSB by using a different chipset, or BIOS limitation
I cannot tell if this is the case, but it seems like this is a design MSI used for OEMs like HP in the days of socket 478 CPUs that could be customized accordingly, nor can I find that model board online to see if I can flash a better BIOS and get this thing to take my P4HT with a 800MHz FSB
I had this CPU dropped from 2.6GHz to 1.6, just because of the BIOS or chipset limitation, if not both
I had a 4500S with a bad motherboard and funky power supply pinout(the motherboard and PSU FF was different, but that's common in SFF systems), so I used a known weak PSU I had from that thing and a Intel PGA370 mobo with corroded chips, and I tested it to see what really happens out of boredom
It blew traces and made them black, so I am glad I used weak parts that were shot