What issues can I have with logic and earth ground?
This article discusses troubleshooting logic and earth grounds for EDI signal monitors in Caltrans cabinets.
You may receive the following fault after testing your 210 or 2010 series signal monitor
I have been doing my annual on a 210 and 2010 model monitor testing and I get the following fault: (the same fault can appear in any Caltrans Model monitor)
|
LGND / EGND ISOLATION TEST PCMT-8000 Output: LGND isolated Monitor Response: LGND-EGND connection found *Test Result: Fail |
| LGND/EGND Isolation Test Description | Verify that LGND and EGND are NOT shorted together inside of the monitor. |
| Test Sequence | No inputs are provided to the monitor. The PCMT tests for a short circuit between the monitor logic ground and earth ground pins. |
| Monitor Response to PASS | Logic ground and earth ground must not be shorted together in the monitor |
The issue is the monitor now has the logic ground and earth ground pins tied together. The causes of this could be a lightning strike, miss wiring of the monitor, or static electricity, causing a short on the board.
- To verify that the logic ground and earth ground are shorted, take an ohmmeter and check pins 20 and Y for a short.
- If you have a short present, your monitor may cause other problems in the cabinet. It is recommended to replace the monitor.
- Repairing this unit is going to be tough because having these two pins shorted could cause multiple damage to integrated circuits on the monitor.
Never connect the logic ground to either chassis ground, AC neutral or earth ground. Doing so can also cause the issue seen above.
|
