17IPS20 Repair -- Fuses and Diagnostics

The 17IPS20 power supply board has a huge plethora of fuses that are worth checking because they can give you a vital clue as to which subsystem has gone wrong. The fuses are on both sides of the board, with through-hole types, and SMD types. In addition, there are a number of low value resistors that can also behave as fuses and go open in short-circuit conditions. In this article we look at some of the vital ones worth checking in the LED backlighting drive part of the circuit.

A very important group of fuses are on the SMD side of the board near Q503 and Q502 MOSFET transistors that produce the high-voltage step-up function. As you can see from the picture in the banner, F502 and F503 will isolate the MOSFETS Q502 and Q503 if they go short. If the rectifier diodes D503 or D504 go short, or any of the LEDs in the matrix goes short, then F500 and F501 will cut them off from the circuit. An additional set of fuses F511 and F512 provides additional protection for the switched-mode power supply circuit that produces the +24 V to 80 V rail. In addition, there are plenty of low value resistors (10 Ω, and 100 Ω) that are worth checking.

Whilst they are not fuses, it is also worth checking the electrolytic capacitor group as they can go short or open and even bulge.

If Q502 has a shorted gate junction, then check Q500, to make sure it is not damaged. Check the low value resistor (10-Ω) R502. If this resistor is open, then chances are high voltage has damaged the MPS3394S IC by entering through its pin 14 (GATE_LED).

If the 17IPS20 board is totally dead, then it is worth checking the main fuse FS100 shown above.

There are also some strange looking fuses such as F102 and F105 worth checking.

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