Batboard

So I have noted there are 2 cooling fans in the 120b/c series.
Some thermal sensor triggers the 2nd fan as needed.
My 120c second fan came on and the room was not that warm.

The fan continued to run after I shut down the ifr.
I am experimenting by using an external 12v supply.
According to the temp test it's about 5 degrees cooler.

Is this an indication one or more of the supplies are drawing too much current?

The fans run directly off of a 12VDC supply and should always be on when the unit is on,

If one if not coming up right away its because the bearings are shot ...replace both.

There is a thermal switch which will cause the fans to stay on until the unit cools off ...its switches the fans to the 12VDC also used for the OXCO option and is always present if the unit is plugged in to AC or DC.

The unit will get hotter when on AC since you have to account for the AC to 15VDC converter losses.

I found normally only one fan runs. When it gets hot the 2nd fan runs, noticeable sound difference.

As before both fans are hardwired directly to a 12VDC supply and will come on with unit powered on.

You have a broken fan with a seized bearing that loosens with higher temp and allows the fan to spin.

Replace both.

There is no circuitry in the COM-120 power supply that switches fans on based on temp with power on ...it will hold both fans on after power off if still warm until the unit cools down.

If you actually meter the connectors you will see that both fans are wired in parallel and 12VDC applied with power on .

The COM-120B and C power supply
The fans get there power from the +12EL display thru cr24( +12minus a diode drop). If the unit reaches hot running, thermal SW1 will connect the fans directly to the +14 supply (they speed up and run even if the unit is put in standby.) +14v thru U7 to +12voven.
Both fans are connected together and run together.
Carl
N0PXJ

Yes, ok Carl, That's what I have discovered, the 14v is applied when hot.