Apple iMac A1419 27" Late 2013 With Intel CPU Core i5 3.2GHz / 8GB RAM 136134545513 and it could be due

and it could be due to a bad grounding pin

Manufacturer Thorlabs Model Number MT1B SKU 19-78411 Ref 23-113093

Includes only the Probe Cable as pictured

Manufacturer Tele Fun Ken SKU 19-69582 Ref 23-99766

Manufacturer Thorlabs Model Number LG7A SKU 19-77777 Ref 23-111863

Apple iMac A1419 27" Late 2013 With Intel CPU Core i5 3.2GHz / 8GB RAM 136134545513 and it could be dueCondition Used Description This item is fully tested and in excellent working order. Fresh install of macOS Catalina 10. 15. 7. Item will come with a 30 Day Warranty. Cosmetically in good condition showing minor scuffs scratches blemishes from previous use. Includes iMac, Wireless Keyboard, Wired Mouse, and Power Cable as pictured. No additional items or accessories are included. Photos are of the actual unit for sale. Inventory is on hand and ready