Odd Symptom PDP 8e Running Programs

Hi - I am looking for some help. I have had a PDP 8e with RK05 drives that has run pretty reliably for many years, but after moving it a strange symptom has come up, preventing it from operating correctly. I am hoping someone can advise. Here is an example 1. Power up drives and PDP 8e 2. Load OS/8 3. Load ADVENT 4. Program loads, asks if I want instructions. I can enter Y or N and the system responds. The familiar scrolling light pattern appears on the front panel to indicate awaiting input 5. As soon as I attempt an action such as "S" (with no quotes) the front panel freezes and I have to CTRL+C to exit ADVENT, dumping me to the dot prompt. Similar issue when running the MUSIC.SV program. I can load the program and get up to the point of entering a song, but when I enter a song name the system freezes on the first note. BASIC works fine however. Which tells me that I have a CPU problem, not a RAM problem but this is just my hunch. Any ideas how to diagnose this? Running MAINDEC programs is always frustrating. I am attempting to load the main DECX8 SYSTEM EXERCISER to see if there are any clues from this as to the cause of the freezing system. . https://www.pdp8online.com/os/os8/os8_cmd.shtml#DECX8 Thanks Bill