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August 28th, 2025 22:33
Exact location of ambient air temp sensor? PT3620
I have an ambient air temp sensor failure on my presicion tower 3620, and was planning on replacing the motherboard with a refurbed board. Where exactly is the ambient air temp sensor located before I buy a replacement mobo?
There is no direction in the manual as to it's location which leads me to believe it's surface mounted on the motherboard. Unlike some of it's older counterparts as well there is no pin header on the mobo for an air temp sesnor.
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ejn63
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August 29th, 2025 12:41
It's usually mounted on the front panel behind the bezel, not on the mainboard. It may be connected into the front panel wiring harness - not to a separate connector on the mainboard.
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JoulesVerne
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August 29th, 2025 13:13
@ejn63 So I had seen this mentioned online also and decided to completely dismantle the front I/O panel to double check, but could find no evidence of it (no daughterboard, obvious sensor etc.) it was just the four USB ports and HDD status light.
The only other cabled element on the front panel is the power switch so other than that and the front I/O there wasn't any sign of it. I know this was the case on older models however.
There is at least one surface mount thermal sensor I could find as it was marked so on the motherboard but unsure if it's exactly the ambient air temp one as it doesn't specify.
If there were a more detailed pinout document or some such I could maybe find out but alas, I'll probably just take the hit on the replacement board as it's not too expensive anyway.
Thank you for the response though it's appreciated.
ejn63
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August 29th, 2025 16:31
Before you replace the board, see here
https://www.reddit.com/r/computers/comments/1gkhljj/subject_dell_precision_tower_3620_ambient/
JoulesVerne
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August 29th, 2025 18:46
@ejn63 Yes this was the only thread I could find also previously relating to the PT3620. My issue isn't the same however. On boot in POST I get an "ambient air temp sensor not detected" error, not an "exceeds thermal limits" error.
After thoroughly checking the documentation, dissassembling the front I/O panel completely, applying new thermal paste and checking for any pin headers on the motherboard was when I'd come to this forum in hopes of there being some way to know exactly where the thermistor is located in order to replace it. The issue was also strangely intermittent and not at all related to system load. Sometimes the fans would just spool to beyond their maximum, and then go quiet again. Stranger still after cleaning around some of the contacts with iso on what I suspected to be the surface mount thermistors now only the CPU fan spins at max, but the chassis fan does not.
From searching some more I'd found that some of the older precision tower models as well as optiplex models had seperate air temp sensor headers on the board, which then went to a thermistor mounted near the front intake. The PT3620 however does not which lead me to conclude that it was surface mount, as well as two small resistors one of which is labeled something like "THRM RST"
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