Hp Z820 Ambient Temp

[James876]

Hi,. HP Z820 workstation Dual CPU, 

My chassis fans are spinning at max because system Ambient Temp is showing a false reading,.  I'm using HP report tool and My CPU's , memory GPU are all low temps, however system Ambient Temp  jumps from 14 - 60 c.  Suddenly and was even reading 120c  recently,.   I read that the mother board power cable has a thermal sensor so I unplugged cleaned and this resolved the ambient temp at 120 c    however again it is still  jumping to a high temp when all my other components are low temps,.  There is more than adequate air flow within the case, I even leave it open and one of the shrouds covering the GPU removed,   could anyone tell me whether the sensor for the ambient temp is within the  CPU,.    the IO cable,.       Or mother board power cable ?

[DGroves]

workstation related questions should be posted in the workstation forum where it stands a better chance of getting replies

the z820 uses a transistor that is embedded in the power on cable for measuring the ambient air temperature when this fails (or is missing) the cpu fans will ramp up to full speed

the solution is to either replace the cable, or replace the bad transistor in your existing cable

ebay cable assembly:

https://www.ebay.com/itm/332629885597

if  replacing the sensor in the cable, it's near the power button board end close to where the speaker wires exit the black heatshrink that covers the cable wires , and it's a common npn transistor you can use a 2n3904 or a 2n222a plastic body transistor as a replacement

note that the existing transistor will have two leads connected together and a single lead connected to colored wires,  match the existing leads  to the replacement and also note which lead connects to which color wire

https://components101.com/transistors/2n2222a-pinout-equivalent-datasheet