635+SCAB as ATX control no backlight after reboot


New member
Hi there,

i have three 635 with a SCAB attached. I want to use them for 19" 1U computers to show IP-Adress, Bitrate, temperatures etc.

I have connected the SCAB with the ATX-cable (WRPWRY14) to the motherboard.

I have set the GPIO pins to ATX Power functionallity using command 28.

Then i have configured my boot up screen with the 635 Wintest programm from your homepage.

In the next step i configured the atx functions no. 1, 2 and 4 (Reset, Power on and LCD off when host off) using command 28 as well.

Now everything is fine. I can boot up the machine, reset it and the display turns off when the host is off.

My problem is when i turn on the machine with the check button of the display it starts and the boot up screen from the 635 display comes up but the backlight is off. When i configured it as boot up state it was set to 100%.

Why doesn't it come up with the backlight at 100%, the rest is working fine?!

Thanks for your help...

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CF Tech

Do you have a floppy drive power cable connected to the SCAB?

Function 4 makes the display look "dead" until the SCAB sees power on the floppy cable.


New member
Yes i have a floppy power cable attached to SCAB-Board.

I have also opened JP8 and closed JP9 as mentioned in the technical documentation V1.1 for the SCAB...


I just have taken a volmeter and checked the voltage on GPIO1.
When the system is off --> 0V
When the system is on --> 5V

I have used the commands "34" to set GPIO1 as ATX Sense
GPIO2 as ATX Power
GPIO3 as ATX Reset

Is there anything else i have to do?
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CF Support

JP2 on the CFA-635 must be open as well.

Note that all of the connections must be present at the time of the boot-state setting (+5v, +5v standby, USB) and the module set up as you would like it to boot when you send command 28 and then command 4 or you will see the behavior as you have stated.