I have doubts about 3200MHz memories working at this rate in these Precisions. 9th generation Intel are limited to 2666MHz and at the time they were sold on the dell website, if I remember correctly, for a short period there was an option to buy the 7540/7740 with up to 4x16gb 3200MHz (not 2x32gb or 4x32gb), but soon that option ran out ...
Has anyone tried to upgrade memory for a Precision 7740 laptop? That is, mem not NOT bought from dell. I tried to install the following RAM -- and failed?  Bought 2 pairs of the following mem. G.SKILL Ripjaws Series 64GB (2 x 32GB) 260-Pin DDR4 SO-DIMM DDR4 3200 (PC4 25600) Laptop Memory Model F4-3200C22D-64GRS   (CAS Latency: 22, Timing 22-22-22-52) Laptop wont boot up and indicated "Invalid memory installed" by LED blink code.  I tried to install all possible RAM module configs - All 2 pairs (4x32 = 128GB total), each module individually (32GB) and each pair (2x64GB) individually . All attempts failed.  It's somewhat unlikely that I had 4 defect RAM modules.  I installed single and double modules as specified in setup/spec guide. The mem spec should meet the memory spec for the 7740 laptop - as far as I can tell. See official Setup and Specification guide for Precision 7740. However, the guide does not mention CAS Latency or time requirements. Does anyone have any experience with mem upgrade? Tech support cant help, because memory is not bought from Dell
Memory upgrade for Precision 7740