Repair notesDemo session
No power on the demo board: a shorted bus capacitor
Three symptom questions, a diode reading near zero on the main bus, a resistance check that confirms a hard short, and C7010 named in under two minutes. Built from a demo session on the demo board.
This is a session on the demo board 820-00000 (Demo Laptop 13-inch), run through the same engine the bench uses, with a simulated meter. The values are invented but plausible; no customer board is involved.
Session facts
- Board
- 820-00000
- Tree
- No power
- Readings to the fault
- 2
- Time to diagnosis
- 1 min 3 s
The path
- +0 s
Session started on the "No power" tree.
- +0 s
What colour is the charge light?
- +8 s
Answered: Amber.
- +8 s
What does the charger or bench supply draw?
- +14 s
Answered: 0.0 A.
- +14 s
Unplug the charger. Disconnect the battery connector.
- +34 s
Done.
- +34 s
Diode mode on the main bus
- +48 s
Reading on C7010 pin 1 (PPBUS_MAIN).
0.012 Vexpected 0.300 to 0.500 V: Fault
- +50 s
Resistance to ground on the main bus
- +61 s
Reading on C7010 pin 1 (PPBUS_MAIN).
0.9 Ωexpected 2 kΩ or more: Fault
- +63 s
Diagnosis reached at 82% confidence.
The diagnosis
C7010 shorted on PPBUS_MAIN
Likely C7010, 10 µF 25 V 0603 X5R, at 82% confidence.
Evidence
- Diode mode on PPBUS_MAIN read near 0 V
- Resistance to ground under 2 kΩ
Fix
Remove C7010, confirm the short clears, fit a new 10 µF 25 V 0603 capacitor.
Donor boards
820-00000 rev A, 820-00001 rev B
Why the tree went this way
An amber light with no current draw says the charger is seen but the bus is not coming up. The first reading is diode mode on PPBUS_MAIN with everything unplugged, because a shorted bus is the commonest cause and the cheapest to rule out. Near 0 V is a fault, which opens the short branch: resistance to ground confirms a hard short rather than a leaky part, and the tree names C7010.
On a board with the bus clear, the same tree plugs the charger in and checks the bus voltage next; low with no short points at the charger controller instead. How the branching works.