Question Rear case-fan light has started to turn on and off randomly ?

[Guusfraba126]

hi guys,

i recently build a new PC as below:

CASE: DeepCool CC560 V2
MAINBOARD: MSI B550 Pro-A
CPU: Ryzen 5 5600 with Thermalright Assassin X 120 SE RGB Cooler
GPU: XFX Radeon RX 6800
RAM: Aegis G.Skill 3200 16GB
PSU: Seasonic G12 GM 650W
SSD: WD Blue SN580 1TB (System is running on this one), Patriot Burst 512GB

Everything has been working great, but since last week i encountered a strange issue. Sometimes the light of the back fan of the case starts turning off for a few seconds and then turns on again. The fan keeps spinning. It only happens with the light of the back fan (not the front fans) and it only happened during gaming and stress testing (Furmark + prime95) so far. It doesn´t seem to happen in idle. It doesn´t flicker or anything, it looks like a very controlled turning off and turning on.

I already checked the fan connectors and reseated them, but i wasn´t able to identify a problem. I deactivated XMP and strangely the problem stopped happening for about a week. So i thought maybe the XMP caused some instability with the power supply or something but today it came back while playing.
Any idea what it could be? Anything i could try to narrow it down? Any help would be much appreciated!

 

[CountMike]

hi guys,

i recently build a new pc. Here is the build:

CASE: DeepCool CC560 V2
MAINBOARD: MSI B550 Pro-A
CPU: Ryzen 5 5600 with Thermalright Assassin X 120 SE RGB Cooler
GPU: XFX Radeon RX 6800
RAM: Aegis G.Skill 3200 16GB
PSU: Seasonic G12 GM 650W
SSD: WD Blue SN580 1TB (System is running on this one), Patriot Burst 512GB

Everything has been working great, but since last week i encountered a strange issue. Sometimes the light of the back fan of the case starts turning off for a few seconds and then turns on again. The fan keeps spinning. It only happens with the light of the back fan (not the front fans) and it only happened during gaming and stress testing (Furmark + prime95) so far. It doesn´t seem to happen in idle. It doesn´t flicker or anything, it looks like a very controlled turning off and turning on.
i already checked the fan connectors and reseated them, but i wasn´t able to identify a problem. I deactivated XMP and strangely the problem stopped happening for about a week. So i thought maybe the XMP caused some instability with the power supply or something but today it came back while playing.
Any idea what it could be? Anything i could try to narrow it down? Any help would be much appreciated!

Which kind of fan is it? Permanent LED colors, RGB or ARGB ? How is it connected, direct to MB or thru a hub ?

 

[Guusfraba126]

Which kind of fan is it? Permanent LED colors, RGB or ARGB ? How is it connected, direct to MB or thru a hub ?

the case has 4 120mm (permanent LED colors) fans. 3 in the front and 1 in the back. they are connected by 3 pin molex connectors and then directly connected to the MB (no hub) via 3 pin on to the 4 pin sys-fan pins. the 3 front case fans are completely fine.

 

[CountMike]

the case has 4 120mm (permanent LED colors) fans. 3 in the front and 1 in the back. they are connected by 3 pin molex connectors and then directly connected to the MB (no hub) via 3 pin on to the 4 pin sys-fan pins. the 3 front case fans are completely fine.

Some causes I can think of:
All LEDs are connected serially to be able to operate at 12v, glitch in any of them would shut them all down.
As they are made to work at same voltage (12VDC max) and 3 pin fans adjust speed by lowering voltage, it's possible that when fan gets some low voltage in order to run at lower speed, LEDs don't get enough volts. They are mostly only on-off and light intensity changes with square wave frequency, not voltage.

 

[Guusfraba126]

Some causes I can think of:
All LEDs are connected serially to be able to operate at 12v, glitch in any of them would shut them all down.
As they are made to work at same voltage (12VDC max) and 3 pin fans adjust speed by lowering voltage, it's possible that when fan gets some low voltage in order to run at lower speed, LEDs don't get enough volts. They are mostly only on-off and light intensity changes with square wave frequency, not voltage.

So adjusting fan speed to be at a consistent speed (and therefore consistent voltage) should fix this issue if i understand you correctly?
If all LEDS are connected serially and a glitch in any of them would cause all of them to shut down, why is only my rare fan doing it?

 

[CountMike]

So adjusting fan speed to be at a consistent speed (and therefore consistent voltage) should fix this issue if i understand you correctly?
If all LEDS are connected serially and a glitch in any of them would cause all of them to shut down, why is only my rare fan doing it?

1. Yes that would supply higher voltage to motor as well LEDs.
2. That fan may have at least one failing diode. Remember old time Christmas tree lights? Those were connected same way and same occurred if one died.

 

[Guusfraba126]

1. Yes that would supply higher voltage to motor as well LEDs.
2. That fan may have at least one failing diode. Remember old time Christmas tree lights? Those were connected same way and same occurred if one died.

1. i just checked bios, the system fans were configured to always run on 7.2V and never change speed/voltage. So this shouldn´t cause the issue then?
So a bad rear fan seems most likely at this point i guess?