The logic board of the iMac (21.5-inch, Mid 2011), model A1311, 2011, 21.5-inch. Known faults are being collected.
No guided tree is live for this board yet. The profile, the viewer and manual entry are there on the free plan, and the first sessions on it build the tree.
Checked on 2026-10-29 against 2 sources: corrected. info 'Late 2011' changed to 'Mid 2011'. iFixit lists 820-3126-A as the iMac 21.5-inch EMC 2428 Mid 2011 board (A1311, iMac12,1, 2.5/2.7/2.8 GHz); macofalltrades ties it to Mid 2011 MC309LL/A and MC812LL/A (APN 661-5936/5937); gotlaptopparts to Mid 2011 MC309LL/A. Apple's identify page lists no Late 2011 21.5-inch iMac. Year unchanged. Revision A is a placeholder until Studio records the real revisions.
Open the board in NextProbe, answer the symptom questions and follow the lit point. The free plan includes three guided sessions a month. Your own boardview and schematic stay on your machine.