A Juniper EX4100-F-12P enterprise switch, retail price around $3,000, sold for under $300 in 'untested' condition. The channel This Does Not Compute bought it anyway. The 48VDC input rails were shorted before a single screw was turned, which explained the price.
Disassembly revealed the full damage: water ingression, rust, corrosion, and at least one violent component failure that physically ripped through multiple PCB layers, destroying inner traces. The burn mark on the lid near the power input was the first warning. A 280-watt power delivery system meeting corroded conductors is what the aftermath looked like inside.
No schematics exist for this unit. Juniper offers no repair path. The switch is now e-waste. Read the original for the step-by-step diagnostic process, because the real value here is watching someone correctly identify a shorted rail, trace the damage inward, and know exactly when to stop. That methodology is worth more than the switch ever was.
[READ ORIGINAL →]