by Jack Goho
Gideon received two failed NEC 104PW161 inverter boards with Micro Fuse chip circuit protectors failing. Rather than performing a failure analysis of the fuse, the circuit was analyzed to assess the possible overuse of the fuse. This was done because the failure rate is beyond the infant mortality and before the manufacturers’ end of life prediction leading to a reliability concern over the fuse. Whether this is a true fuse issue or a design issue, this is the first step in resolving the matter.
This card is a fluorescent backlight inverter for LCD based displays. It is composed of DC/AC inverter circuit, a luminance control circuit and boosting transformer. The luminous control circuit controls the luminance of cold cathode lamps for LCD backlighting unit. The boosting transformer used to translate low AC voltage that can be obtained from a DC/AC inverter circuit to the high AC voltage.
- DC/AC inversion by center tap transmitter circuit
- Pulse width modulation circuit
- Alert circuit for malfunction
- Externally commutated driving system
- Input supply voltage is 12V
- Oscillation frequency of 55KHz
For each of the three cards, a plot was captured showing the run-time operation. For this operation, the time base was configured to a 10us interval, to show continuous current draw, as well as the AC ripple. Additional mathematical measurements have been included in the plots to make comparisons easier for the customer.
A table was made of the measured electrical parameters of the board and waveforms. Sample 3 was consuming 40% more current than sample 2 which was drawing 10% more than sample 1. The ripple current characteristics were different for each board. This data collection process lead to the conclusion and fixed the problem.
Gideon is the “GO TO COMPANY” for failure analysis. Why? Over 40 years in the business. Electrical engineers who have designed with redundant systems with over 38000 components. We can reverse engineer, select components, design PCB, perform failure analysis, and from start to finish we know the entire process. Call us today.