What's inside a cheap network cable tester?

Описание: Network cable testers from eBay. Buy cheap, buy twice!
Save your money and buy a different model, as it doesn't take much to kill these ones.
Schematics are at   / 2851753161803028  

PDF schematics: https://drive.google.com/file/d/1uP1o...

INDEX
0:00 Index
0:10 Introduction: Cheap network cable testers from eBay
0:25 What's fried them? Probably not PoE
1:17 How they're supposed to work
3:08 How they're NOT supposed to work
3:35 What's inside?
4:12 Receiver schematic
4:43 Emitter schematic
5:00 Wire mapper theory of operation
6:32 Tone generator theory of operation
7:41 Scoping the tone outputs
8:02 Design flaw: is the tone generator cooking the wire mapper?
8:40 A simple suggestion for improvement
9:43 Scoping the faulty tone generators
9:58 Hotspot spotting with a thermal camera
11:40 Power consumption testing
13:37 Testing with tone generator removed
14:50 Testing with tone generator re-added and wire mapper removed
15:56 Removing even more tone generator
16:15 Wire mapping into a network switch? No problem
16:52 Tone generating into a network switch? Magic smoke time!
17:43 Conclusions

Music is from a 30-year-old Amiga demo, check out Peter Salmonsen's YouTube channel at    / psalomo