Replacing NTC Thermistor with an SMD Resistor

Thread Starter

Aleksandr Gonzales

Joined Jan 15, 2016
27
1.JPG

Hello masters! This is the diagram from my motherboard's PWM Controller (Richtek RT3606BC). I experience overheating flags on VRMs, even if it is not literally overheating. There are two NTC Thermistors in my motherboard, on the top side, I measured it with 68k Ohms on ambient temperature, as I put heat on it, its resistance goes down. On the bottom side, there is also an NTC Thermistor with that diagram (above). However, when I measured it, it is constant 12.09k Ohms, regardless of heat. So I suspected that I have a faulty thermistor, so I replace it with a resistor (98k Ohms), but still it shows 12.57k Ohms, so I replaced the R1 with 0.5M Ohms, and I get a constant 67k Ohms on the NTC Thermistor (Resistor) part. Am I doing this right? Hehe. Just experimenting and no advanced knowledge with this. Hehe.
 

jpanhalt

Joined Jan 18, 2008
11,088
On the bottom side, there is also an NTC Thermistor with that diagram (above). However, when I measured it, it is constant 12.09k Ohms, regardless of heat. So I suspected that I have a faulty thermistor, so I replace it with a resistor (98k Ohms), but still it shows 12.57k Ohms, so I replaced the R1 with 0.5M Ohms, and I get a constant 67k Ohms on the NTC Thermistor (Resistor) part. Am I doing this right? Hehe. Just experimenting and no advanced knowledge with this. Hehe.
Unclear whether the NTC is still in the circuit. 98k ||500k = 82k; however, 68k(assumed for NTC)||500k = 60k. If the NTC's actual resistance is actually 12.09k then regardless of R1, the resistance across it in circuit will not be greater than 12.09k. You also have to consider R2. Forgetting about the comparator, if you measure across Rntc in circuit, then you could view that as (R1 +R2)||Rntc. What were the original values of R1 and R2?

When you ask whether you are doing it right, what are you trying to do? Measuring resistances in circuit is always problematic. You are measuring a whole circuit, not just across a single component.

Since you removed it, I suggest you measure the NTC out of circuit and test whether it responds to temperature change If it is defective, why not replace it so the safety circuit works as designed?
 

Thread Starter

Aleksandr Gonzales

Joined Jan 15, 2016
27
Unclear whether the NTC is still in the circuit. 98k ||500k = 82k; however, 68k(assumed for NTC)||500k = 60k. If the NTC's actual resistance is actually 12.09k then regardless of R1, the resistance across it in circuit will not be greater than 12.09k. You also have to consider R2. Forgetting about the comparator, if you measure across Rntc in circuit, then you could view that as (R1 +R2)||Rntc. What were the original values of R1 and R2?

When you ask whether you are doing it right, what are you trying to do? Measuring resistances in circuit is always problematic. You are measuring a whole circuit, not just across a single component.

Since you removed it, I suggest you measure the NTC out of circuit and test whether it responds to temperature change If it is defective, why not replace it so the safety circuit works as designed?
R2, as I measured it, around 10.2k Ohms, while R1, is 2.09k Ohms sir.

"You are measuring a whole circuit, not just across a single component." - This is what I realized sir, so I just focused on getting the same value on the NTC Thermistor.

"If it is defective, why not replace it so the safety circuit works as designed?" - I don't have sir the replacement parts or any donor boards, for I am just doing this as DIY, trial and error. Hehe. I just want to explore or try to solve the flag, but I accepted that the board is already gone. Hehe.
 

jpanhalt

Joined Jan 18, 2008
11,088
Resistors are usually marked with a value. Through hole are color coded; SMD usually have numbers on them. It is not what you measure them as in circuit that matters, if you want to understand. It is what their actual value out of circuit is or what they are labeled as that matters.

Now, if you just want the thing to run without shutting down when it overheats, isn't that what you have already done? Or did it still not run after you made those changes?
 

Thread Starter

Aleksandr Gonzales

Joined Jan 15, 2016
27
Resistors are usually marked with a value. Through hole are color coded; SMD usually have numbers on them. It is not what you measure them as in circuit that matters, if you want to understand. It is what their actual value out of circuit is or what they are labeled as that matters.

Now, if you just want the thing to run without shutting down when it overheats, isn't that what you have already done? Or did it still not run after you made those changes?
That's sir where I get confused, because the SMD Resistors (R1 and R2) on my motherboard doesn't have any markings, so I get no reference, just plain black, as I recalled it. No schematics or diagram. Hehe. I just get my diagram from the PWM Controller chip.

"Now, if you just want the thing to run without shutting down when it overheats, isn't that what you have already done?" - Actually sir the board is running and not shutting down, it just happened that it sends signals to the CPU to throttle down for a VRM Thermal Flag. So regardless of load, my CPU (i7-7700) runs only at 0.80 GHz, fixed.


"Or did it still not run after you made those changes?" - This is where I get scared of sir. Hehe. I don't want to blow off everything, with what I have done. Does my modications will not cause fire. Hehe
 

jpanhalt

Joined Jan 18, 2008
11,088
You have bypassed a safety mechanism. Anything bad that happens is now on your shoulders, not mine. Particularly, if there is the potential for fire, I would not do what you have done nor condone it.
 
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