Indigo 1: Dead Serial Port?

[hbent]

I have an Indigo 1 that's been running just fine for many years. The only weird thing about it is that no matter what I set in the PROM, it won't auto boot. This isn't really a problem, I just hook up a serial cable when starting up the machine, type "boot" at the prompt, and we're off on our merry way. Now, however, all of a sudden the machine is stuck at an orange LED (and doesn't chime, or make noise of any sort) if I have a serial cable connected to port 1 in any way - connected on the other end, not connected on the other end, doesn't matter. If I unplug the serial cable it chimes, starts right up, no problem. Unfortunately that isn't going to work for me as even though I have a keyboard and monitor connected, it never gets far enough to initialize them. Any suggestions on what to look for? There's nothing obviously wrong with the port and both of my 8 pin serial cables seem fine. I haven't yet pulled the CPU board but I suppose that's the next logical step.

 

[Elf]

Edit: With apologies, I no longer wish to have involvement with SGUG or SGI communities in general,
and have also chosen to remove all of my content. Many things have changed since I co-founded, named, and ultimately
then left SGUG. There are many good people around, to whom I apologize for frustrating by removing these things, and
also many petty people that over the years whittled down both the enjoyment as well as sense of obligation I used to
feel to anyone else regarding what was ultimately just a hobby. Unfortunately one of the latter now writes the rules
and so it is time for me to take my things and go.

This message will replace all of my previous forum posts because deleting threads that I started would have removed
other peoples' posts.

 

[weblacky]

I’m unsure about SGIs specifically but it’s often common, modern, practice to check for cable insertion by monitoring the grounding on the port. So I’d agree with Elf, likely there is a short. Now perhaps not a dead short, but even a high-resistance connection of rust or something can trigger such a feature.

I'd suggest (since you have two serial ports) that you attempt to probe two configurations:

1. Ground shield to pin (every pin).
2. All neighboring pins for connections between each other.

Now, let's be clear here. This port is already soldered to the PCB and already has IC connections. So pins will be connected in some fashion right now. I suggest you use compare serial 1 port with serial port 2. Do probing 1 & 2 on serial port 1 and record the values, then do it again on serial port 2 and compare values.