ATX Power Control Issue


New member
I am using a CFA635 TFE KU (USB) + SCAB board paired with a mini-ITX Linux box (Debian 2.6.26), set-up for ATX power control

Observed Operation
The Display turns on with Vstandby vs Vswitched, and I can always ‘RESET’ the Display by depressing the Green Check/Enter Key for 4 seconds, regardless of what powered state the MB is in. If the MB is powered on, I can reset the MB using this function as I would expect.
I can power cycle the MB off or on by depressing the Red X/Cancel Key for 4 seconds. However, the Display remains on and reads ‘POWER OFF’ regardless of what powered state the MB is in. Fans power on and off with MB Vswitched as expected. Now once in this ‘POWER OFF’ Mode, I have to execute a RESET in order for the Display to ‘wake-up’.

I know I am executing the command functions correctly, because I can change the default display, and am getting the ATX and Boot State set notifications and return packets, and before I executed these commands I was not able to power off/on or reset using the keypad. Also, I was able to send the ATX command with a 242, 244 and 246 data parameter, and lose the ability to power the MB on and off (244, 246). Oddly, the reset function works in either normal (240, 244) or inverted (242, 246) mode.

Expected Operation
The Display and MB to turn on via the Green Check Key with Vswitched not present, and to turn off with the Red X/Cancel Key with Vswitched present. I measured Vswitched at J8-6 to be 0.38VDC with the MB in the powered down state and 4.98VDC in the powered up state.

I came across another thread with the same indications, however the resolution was not contained in the thread.

Anyone have any suggestions?


SCAB-Connected floppy power connector attached to J3 (Switched power)
-JP8 Opened
-JP9 Closed
-Connected MB GND to J8-1 (GND)
-Connected MB Vstandby to J8-2 (+5V Always on)
-Connected MB PWR SW J8-5 (GPIO2)
-Connected MB Reset SW to J8-4 (GPIO3)

-JP2 Disconnected

-Modified example-635.c to set ATX control, values set by sending command 28 \240,
followed by command 4 \0. I left the GPIO configuration in the default state.

I have verified the MB Pwr& Reset function as ‘normal polarity’ according to the following method from another post:

If you have a volt meter, you can take three measurements to figure it out.
1) call one pin of the power switch header's pins "pin A", and the other "pin B"
2) with the motherboard powered by Vsb but not powered up, and nothing conected to the header, measure the voltage on pin A and pin B relative to the black wire of a HDD connector.
3) while the black lead of the volt-meter is still connected to a black wire of the HDD connector, use the red lead's probe from volt meter to short pin A to pin B (this is equivalent to pressing the power switch, and the PC will power up). Note the voltage reading.
4) You will typically find that one pin stayed at the same level (either ground, 3.3v or 5v) and the other pin went from the opposite level to the same level when they were shorted. The pin that changed is the pin that needs to be connected to the CFA-633. It either needs to have normal (went from "high" to "low") or inverted (went from "low" to "high") polarity.
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