Hi all,
Ive got a reoccurring issue that has been effecting a couple of dedicated machines that operate remotely. Users are reporting that their systems are unable to turn on. Walking them through the troubleshooting, there is no issues with the monitor. Power is being applied, the system lights turn on. We can confirm the network activity lights on the LAN port and the router has negotiated a link speed. But if we log into the router, we see no packets coming from the PC.
Now, the weird part. When the computer is shipped back, it magically starts working again. Ive tried running a memtest to see if maybe its bad ram, but it always comes back passed. I believe the issue is due to a multiport pci serial card. Sometimes if the cable is removed that connects to that pci, the system will boot. Other times, it completely kills the pc. Until of course it gets shipped back, then it will work again.
Ive really hit a dead end with this issue. Im not sure how to diagnose a no post situation without physically being there. At the very least, I wish I could replicate the issue in person. Unfortunately, the issue is occurring with multiple computers and pci cards. Doubtful its a one off bad piece of hardware.
If anyone has any experience troubleshooting a no post situation remotely or has had issues with pci cards, I’d really appreciate it!
Now that is an interesting idea. I cant go into to much detail about the exact components but this particular port drives a DC motor. Power is injected to drive the motor.
Tbh, im not very familiar with ground loops. Have you had experiences with ground loops before?
I appreciate the quick response as well!
On one hand, that does sound suspicious. It’s an external factor and it’s unusual.
But on the other hand, you said that having it not plugged in doesn’t consistently see the thing working, which doesn’t really mesh with what I’d expect if it’s the cause.
You can get optical isolators for serial ports. Those basically run the signal into an LED and then to another LED, which keeps two separate isolated electrical system; those will eliminate ground loops. I haven’t looked into them for serial ports, but I was looking at hooking up a breadboard to USB at one point, and there it seems to be kinda a best practice for USB device development work, to keep any mistakes from damaging a connected computer system.
https://www.amazon.com/rs232-isolator/s?k=rs232+isolator
In your case, it sounds like you are also using the serial port as a power supply, so you might want something that can provide external power:
https://www.amazon.com/External-powered-Repeater-Mini-size-PhotoElectric-Full-line/dp/B00GI9GRMC
It might also be possible to use an isolation transformer, which would be simpler and possibly cheaper. That would, I believe, provide ground isolation without providing protection against more exotic things, like a short in your external device frying a serial controller. I’ve used isolation transformers for coax TV to avoid ground loops, so I imagine that it must be possible to have them handle serial port speeds. But when I search for “RS-232 isolation”, everything I see seems to be opto-electric.
If you can change the serial port being used, maybe also use a different serial port interface, like a USB serial interface.
Ooooo now this is something!! Ive always had a hunch that the way power is being injected into the motor was causing the issue. The serial device is connected by a DB9 port. The RS485 signal A, B and ground then gets accompanied by power to drive the motor. The serial port from the computer goes into this power injecting box and then the box goes to the moto and controllerr.
The grounds should be connected correctly. But now youve got me thinking about these boxes. Modifications have been .are to them overtime, so its totally plausible that something in there is causing a surge to get back into the computer.
Thanks for the response!
RS232? RS485? RS422? Not that I know much difference between them, but just to satisfy my own curiosity…
My experience with ground loops is primarily from audio equipment. The last one I remember was probably 20 years ago. I had two different devices were plugged into two different outlets on opposite ends of the room. One was either a TV or a computer, providing an analog audio signal to a stereo system. Every time I connected the coaxial audio cable, I got a horribly loud 60hz hum. The ground potential of the two systems were slightly different, and the difference was being carried across the shield of the coaxial cable. The amplifier was boosting that difference, and the result was the overpowering hum.
In my case, the workaround was to snip the ground prong on the amplifier and let it float. I generally wouldn’t recommend that.
I kinda doubt you have anything plugged into that port when you’re working on it in your shop. Definitely have them try disconnecting everything plugged into that port and see if the problem goes away.
Are both the motor controller power supply and the computer plugged into the same outlet? If not, get an extension cord and try that.
Power to all components is provided through a dedicated power supply. If the computer was on, I would be able to get direct readout of voltage and amperage. As for the serial ports, some devices use RS232 and some use RS485.
The ground loop certainly seems to be the most plausible cause. And when its in the shop I’ve got exact replicas of the system. I just cant seem to replicate it no matter how hard I try.
For context, Ive stuck a system in a fridge to see if possibly cold temperatures correlate and was still unsuccessful. At this point I wonder if there is interference coming from an outside source and thats why I cant pin it down.
You’ve given me a lot to think about! I greatly appreciate the responses.