MD-HMI420 - all LEDS on

[cdenk]

Have  T100MD888+, 1 EXP4040, and MD-HMI420. All the LEDS both red and green are on. Online monitoring shows only one green should be on. Otherwise the PLC including the HMI seems to be operating normally. Removing the EXP4040 and plugging the HMI directly to the T100MD888+ the LEDS are all off.

Assuming it a defective chip (which one), since many of the I/O's are not being used at this time, are there other chips I could borrow on one of the boards until I can order a replacement?

[support]

From your described symptom, there seems some damage to the EXP4040 expansion I/O buffer chip (usually caused by hot plugging or unplugging the expansion connect without turning off the power). Try replacing the two 74HCT14 near the left side expansion connector on the EXP4040.

[cdenk]

Thanks for the quick reply. Wasn't near the expansion connect, but was working near board that support the ADC, and do have both Vref and PLC power on board. Am careful about power down when plugging, but things happen.