When you insert a cashcard into a IU, it should lit up for seconds to indicate reaminng value. If cashcard remain < $5, it will remain litup.
If cashcard never, or intermittently, lit up to indicate price, either cashcard spoils or IU spoils. Try using a proven working cashcard to confirm.
If confirm IU spoil, can go to any inspection centers in Sin Ming road to check FOC. No need to book appt and no need any letter. I went to VICOM twice. The 2nd time I went, the technician confirmed cashcard spoilt. But before that I already ganna thrice passing through ERP gantry without any beeps or deduction within a week. The technician filled up a form to indicate I have a faulty cashcard and advised me to go LTA nearby to appeal. The appeal took only 5minutes where the lady accepted my fault report and checked through the system to confirm got 3 recent summons against me. She kindly waived all penalty and the ERP charges. So I saved $30 plus the ERP charges, haha.