48DY8 is a Dell Precision T1700 motherboard.

Many models use the same sensor.  I recall a video where a user put 2.4K ohm 1/4w resistor on the bottom and made the error go away.

https://www.youtube.com/watch?v=-244tPCFWog

No idea what it is. I never bother trying to fake it because the sensors are not expensive.

https://www.ebay.com/p/1304656531

NG578 thermal sensor.

Using a straight resistor may allow your computer to work, but it won't modulate the fan speed.  So you'd have either a noisy (full fan) machine that's cool, or a quiet (low speed fan) that runs hot.

The thermal sensor may just be an 2N3904 NPN transistor with Collector and Base connected and used as one lead, and Emitter as the other.   See here, (search for thermal sensor) to see how its done in an optiplex.  See here for a blog and here for a datasheet for more background.

@k.neo 

@WizardOfBoz2 

So that's interesting but I hate jumping thru hoops.

Links seem legit so others have done the work.

It does however give me much more info.

Transistor 2N3904 B09M3VXR24

analog  an137f

3904 Base and collector tied.

@speedstep thanks for the link.

As it happens I've been watching two electronics channels on youtube:

Mr. Carlson's Lab: The Canadian electronic equivalent of Bob Ross ("The Joy of Painting")

EEVBLOG: The Australian electronic equivalent to Robin Williams on speed.

Both are super useful and interesting, both have very good production values (Paul Carson uses a tube mic and the videos are superbly produced).  Anyway, I am going to revamp my guitar amp (a Fender tube amp called a Prosonic) and need to 1) replace capacitors, and 2) ensure that the tubes are in good shape, and 3) run down any noisy or microphonic components.   Carlson has published designs for a very good capacitor tester (super sensitive to series resistance) and a very good noise sniffer.  So I was going to build both of these and get my amp in really top shape.  Also (and this shows me to be a real dinosaur) I was going to build a very high-end battery eliminator for the VTVM I built long ago.

The transistor and IC kits and SMC resistor and capacitor books are amazing values. I'm trying to figure out which kits cover the most ground wrt the components I need.

Ideally, though, Dell just uses the same 2N3904 NPN transistor for thermal sensing.  It may be finding the wiring, with the proper plugs, will be the hard part.

Thanks again.

@WizardOfBoz2 

Amazon is Great when I want something in a few days. 

https://www.digikey.com/ is what I use when engineering something that is to be sold on a regular basis.  They have been around for decades and are one of the few places left that has Name Brand parts and boards and assemblies and heatsinks etc.   ALL of my local stores like Radio Shack, Heath Kit Zenith, Lafayette Radio, and even the remaining TV and HIFI shops are long gone RIP.

Digikey and Jameco are still around

https://www.jameco.com/

I do miss the Radio Shack stores but Walmart and Amazon Killed them.

Want to run MSDOS on your Newer Dell model that has removed floppy?

The Gotek is for you.  Phils computer lab hooked me up with these.  If you buy one you want the upgraded model with 2 buttons and a knob so you can emulate 100 floppies at a time.

https://www.youtube.com/c/philscomputerlab

Gotek Floppy Emulator
https://www.youtube.com/watch?v=taFP1J_lZBI

https://www.amazon.com/dp/B08XVS5Z7J

You hook these up to your modern Dell using USB to Floppy cable and 5.25 inch to 3.5 floppy bay adapter.

https://www.amazon.com/gp/product/B07WCRF9H

You also want a flash that does not stick out to get broken off.

SanDisk-SDCZ33-032G-B35 B00F3F3FC2

@WizardOfBoz2 

Then there's this engineer  Raphtec who made his own 24 to 8 pin adapter.

dell power supply adapter

Works on Dell T1700, Inspiron 3650, Precision 3620, Optiplex 9020, etc.

@speedstep Yup.  We live in a charmed age: we can get a  LTC1286 0.05% voltage reference delivered next day.  But there's few local stores that you can wander through and look at electronic kits and such.  I miss that, too.  Then again, I can build a 0.05% VOM calibrator for less than 20 bucks in parts!