Hi all, hoping someone recognizes this chip or the reference design.
The device is a cheap Apple Find My–compatible Bluetooth tag, bought at ACTION sold under the name Fresh 'n Rebel "Smart Finder" (model 6ATAG72R).
The PCB silkscreen reads "4B-SF18-OMAAF-1.0.1"
The main IC is QFN, 32-pin, with a blob of blue lacquer/dot-of-paint covering the middle of the marking. Acetone is not effective against the colored dot.
What I can read on the main IC despite the lacquer dot:
- Line 1:
...868... - Line 2:
55...CM - Line 3:
B0T0720
Board has 8 labeled test points (from T1 to T8).
What I've done so far:
- Confirmed via continuity: T2 = GND (also has continuity to the metal can of the 32 MHz crystal, which tracks (can shields are usually grounded)
- Mapped average DC voltage on every test point with the oscilloscope (device powered, idle):
- T1 = 3.16 V
- T2 = GND (0 V, confirmed above)
- T3 = 3.16 V
- T4 = 3.16 V
- T5 = floating reads an unstable -2.88 to -2.91 V
- T6 = 3.17 V
- T7 = 3.16 V
- T8 = 3.16 V
https://i.redd.it/i1i83co0pbph1.jpeg
Source: r/hardwarehacking · by /u/wannabe_sci
