Checking the maintenance manual it appears to be a "RTC INTERRUPT ERROR". I've no idea what this mean, but checking the manual it says just replace the entire board.
Somewhere on the system board is a chip that contains real-time clock (RTC) functionality. If desired, software can configure the RTC to generate a hardware interrupt in certain conditions. Normally, the RTC is not configured to generate an interrupt.
The power-on self test (POST ) will be testing the RTC functionality, including the ability of the RTC to generate an interrupt.
If this was an IBM AT of mine, I know that the IBM AT motherboard has a dedicated RTC chip, the MC146818, and the interrupt from that, IRQ8, heads off to one of the two 8259A interrupt controller chips. Using suitable test equipment, I could see whether the interrupt failure problem is because:
- The MC146818 is not generating the interrupt; or
- The MC146818 is generating the interrupt, but the interrupt is not reaching the 8259A; or
- The interrupt is reaching the 8259A, but the 8259A is not processing it.
I do not see mention of the RTC in the maintenance manual for the T3100. The maintenance manual for the T3100/e is a different story; it states that there is a MC146818 chip. Is there a MC146818 chip on your system board? Look for 146818 (or similar) because the chip may have a different prefix than MC.
You can see where this is going. You may need to replace chip on the system board.
Another possibility that I can think of is system board damage created by a leaking RTC/CMOS battery. Looking at the maintenance manual for the T3100, the battery connector (PJ1) on the system board is right next to one of the two 82C59 interrupt controller chips. Quite suspicious. Have you inspected the insides of your T3100 yet?