jcas

This is a tale of stupidity and dumb luck, enjoy. Yesterday, I was messing with a ML1200 that has only one port, and decided to have some fun with ASCII writes. Because the controller must switch its channel config to ASCII after I download the program, it sits in remote program after a download. So, I enabled S:1/12. I opened up hyperterminal and connected to that port only to notice I screwed up and was sending a non-stop loop of the same string, ad nauseam. So, I went to reconnect using default comms by holding down the DCOMM button for a second. No dice. Couldn't connect. Checked hyperterminal, even in DCOMM, it was still receiving an ASCII string loop. At this point I tried to connect different I/O modules to it in an attempt to get it to fault. It refused to fault. Realizing I was stuck, I called tech support. Got laughed at, and told my best bet would be to get another ML1200, put in a memory module, create a blank program with S:1/11 enabled, and put that memory module in to my looping ML1200. The problem with that is that I don't keep a bunch of ML1200s lying around. I decided to go to work taking the whole thing apart and discharging every capacitor I could find, hoping that one of them held charge to the memory. This still didn't help. It wouldn't lose its memory, it wouldn't fault. I put everything back together and just left the front cover off so that I could probe around the different ICs. During the process of voltage checks, I accidentally shorted two pins of U10 together. By the grace of the PLC gods, this cleared the memory and faulted the controller. I was free. The chip I shorted the pins on was just under the front cover, top left of the first board. It is labeled as U10. The specific pins were on the right side of the chip, 3rd and 4th from the bottom respectively. Shorting these will drop your program.  I'm not sure that anyone else will need this information because I'm likely the only person dumb enough to get themselves cornered like this. However, I'm posting this in the hopes that maybe, just maybe someone is as ignorant as I am and can find solace and solution in this story.

Here's a photo of the pins.

I've always prepared myself everyday like this: On any given service call, expect a punch list of issues from the past 20 years.