TWControls

Are there any conditions on the JSR?  If it is always execute the same as the main routine then the timer will function the same.  However if you enable a timer in a subroutine then stop executing the subroutine, then the DN it will not be set when the timer times out.

Do you have a PLC you can learn on?  There is no better way to improve you skills then browsing forums and trying to solve over users' problems. C++ and SQL are good to know but if you are building on your PLC skills then you may look at learning SCADA systems and data acquisition.  We have lots of free lessons at the following link. https://www.theautomationstore.com/rslogix-500-industrial-control-panel-trainer-lessons/

Make sure that you add it to your I/O Configuration on the left pane of RsLogix.  Beyond that you should be good.

I've ran the PCIS software on DOSBOX box using W7 64bit. https://www.theautomationstore.com/how-to-run-the-allen-bradley-pcis-software-under-windows-xp-configuring-dosbox/

The solid red fault light will not be recoverable.  Chances are you have an internal hardware problem that is also affecting the LCD.  But even if the LCD was working, you wouldn't be able to clear that fault.

Yes but I've got one sitting here in my junk pile, no LCD screen and a solid fault light.  There is still no clearing a solid fault light.

The red fault light. Is it on all the time or blinking?

Is it solid or flashing?

I didn't look up error 21 until now.  Where did you see 21h was a user fault code?  It is an expansion power fail.  See attached.  Since you only have one I/O module, it would be my first guess 21h.pdf

The only problem that could arise if it had a printer attached to that serial port. Otherwise typically that port will be ready to upload.

I didn't see to have you check for an eeprom. Yes I don't see where you have anything to lose by trying.

That's going to make it complicated. Depending on how complex it is you may be able to get somebody write a program for it. Do you have any wiring diagrams or basic description of operation? Also while you're at it you might as well upgrade that to a modern PLC if you decide it's worth the investment.

Is a batteries dead then there is no way to recover the program. Your best that's going to be to try to get a copy of it from the OEM. Are they still in business?

Unfortunately you are probably going to swap a lot of parts to find the culprit.  How many I/O modules are there? One thing I ran into once that may be of help if module 2 continues to show the fault.  I had a system that kept getting a fault on a specific module and it turned out to be the outgoing connector in the module to the left.

What I'm saying is post it here so we can see what can cause the user fault.  Without that information there is nothing anything can do to help.