Programming KBC IT8987VG ASUS TUF FX506L RT809F+PEB
Dear friends, I want to share my experience repairing an ASUS TUF FX506L gaming laptop motherboard: DABKXDMB8E0_F_BKXD. Boardview and schematic are available, as well as the BIOS and ITE ROM.
When the customer brought in this laptop, it was initially dead; it showed no signs of booting for any reason. After hours of measurements, checking each stage, MOSFET, and seeing if there was a short circuit in any capacitor, I discovered a strange 0.7V leakage voltage on the 3V_S5 rail, particularly on the PL9 coil, with the board not powered on. There were 3V_LDO and 5V_LDO voltages, which indicated at least that there was no short circuit in the components that should be supplying these main voltages, which would be the PU12 battery charge controller, KBC KU1, and other separate components.
I deduced that if it wasn't showing any signs of starting up by pressing the power button, and in addition to some voltage inconsistency on the 3V_S5 rail, which by the way should be 0V if it hasn't given the power-on command yet, it meant that the 3V_LDO voltage was being returned to this rail for some reason. Following the lines, when removing the KR1 resistor that feeds the KBC, the voltage leak on the 3V_S5 rail disappeared, clearly indicating that the KBC was perhaps leaking and not shorting out. I had some IT8987VG (BGA encapsulated) spares I had purchased on Aliexpress, which were ready to mount, reballed.
So, with the soldering station at 390° and 75% air, I removed the KBC and inserted the replacement. I also re-soldered the KR1 resistor to power the KBC. It was time for the crunch, and the computer responded, of course not as I expected, but at least there were signs of life: the power LEDs and the battery were on. I tried to turn on the board with the power button, but it didn't respond; it clearly had a different firmware or simply didn't have it. I had to program it. PROGRAMMING THE IT8987VGA WITH RT809F AND PEB1 Programming the KBC requires a bit of work, but it's not complicated. You just have to pay close attention to the pins on the motherboard's keyboard connector, where each of the lines we'll connect to the adapter and PEB1 of the RT809F programmer should go. The lines are as follows:
I didn't use line 12 of the flex cable that goes to PEB1 of the RT809F because it was damaged, but you could use it, or use a flex cable that specifically adapts to the motherboard's keyboard connector and the PEB1 adapter connector. You also need to connect the PEB1 adapter's GND to the motherboard's GND. That's all. Once the board is powered up, you should be able to read the IT8987VG with the RT809F software. In the RT809F software, you need to manually specify a couple of things.
The component to read, which in this case should be IT8XXX_ISP @PEB-1. Then, set the Set Lines to the values that correspond to KSOX and KSIX, respectively, with their pins on the PEB1 adapter. Select Read and connect the motherboard. It doesn't always work immediately; you'll have to try several times until it works. Perhaps it's due to the length of the cables connecting the motherboard and the PEB1, or for other unknown reasons. Be careful; if it stops reading and doesn't enter ISP mode, it could be due to a loose solder connection, or, as happened to me, pins 24 and 25 of the motherboard's keyboard connector were left connected.
Save the read file. Once this is done, simply load (Open) the KBC firmware in the RT809F software and press Write. Again, if it doesn't work on the first try or freezes, you should try again directly: select IT8XXX_ISP, open the file to load, press Write, power up the motherboard, and wait for it to enter ISP and burn the file to the new KBC. Here are some photos of the work done.
When the customer brought in this laptop, it was initially dead; it showed no signs of booting for any reason. After hours of measurements, checking each stage, MOSFET, and seeing if there was a short circuit in any capacitor, I discovered a strange 0.7V leakage voltage on the 3V_S5 rail, particularly on the PL9 coil, with the board not powered on. There were 3V_LDO and 5V_LDO voltages, which indicated at least that there was no short circuit in the components that should be supplying these main voltages, which would be the PU12 battery charge controller, KBC KU1, and other separate components.
I deduced that if it wasn't showing any signs of starting up by pressing the power button, and in addition to some voltage inconsistency on the 3V_S5 rail, which by the way should be 0V if it hasn't given the power-on command yet, it meant that the 3V_LDO voltage was being returned to this rail for some reason. Following the lines, when removing the KR1 resistor that feeds the KBC, the voltage leak on the 3V_S5 rail disappeared, clearly indicating that the KBC was perhaps leaking and not shorting out. I had some IT8987VG (BGA encapsulated) spares I had purchased on Aliexpress, which were ready to mount, reballed.
So, with the soldering station at 390° and 75% air, I removed the KBC and inserted the replacement. I also re-soldered the KR1 resistor to power the KBC. It was time for the crunch, and the computer responded, of course not as I expected, but at least there were signs of life: the power LEDs and the battery were on. I tried to turn on the board with the power button, but it didn't respond; it clearly had a different firmware or simply didn't have it. I had to program it. PROGRAMMING THE IT8987VGA WITH RT809F AND PEB1 Programming the KBC requires a bit of work, but it's not complicated. You just have to pay close attention to the pins on the motherboard's keyboard connector, where each of the lines we'll connect to the adapter and PEB1 of the RT809F programmer should go. The lines are as follows:
| CONECTOR KCN6 | KSO (MY en bdv) | KSI (MX en bdv) | FLEX PEB1 Y RT809F |
| 30 | KSO7 | 1 | |
| 29 | KSO0 | 2 | |
| 28 | KSI1 | 3 | |
| 26 | KSO9 | 4 | |
| 24 | KSI5 | 5 | |
| 23 | KS03 | 6 | |
| 22 | KSI4 | 7 | |
| 21 | KSI2 | 8 | |
| 20 | KS01 | 9 | |
| 19 | KSI3 | 10 | |
| 18 | KSI0 | 11 | |
| 16 | KSO5 | 13 | |
| 15 | KSO2 | 14 | |
| 14 | KSO4 | 15 | |
| 12 | KSO6 | 16 |
The component to read, which in this case should be IT8XXX_ISP @PEB-1. Then, set the Set Lines to the values that correspond to KSOX and KSIX, respectively, with their pins on the PEB1 adapter. Select Read and connect the motherboard. It doesn't always work immediately; you'll have to try several times until it works. Perhaps it's due to the length of the cables connecting the motherboard and the PEB1, or for other unknown reasons. Be careful; if it stops reading and doesn't enter ISP mode, it could be due to a loose solder connection, or, as happened to me, pins 24 and 25 of the motherboard's keyboard connector were left connected.
Save the read file. Once this is done, simply load (Open) the KBC firmware in the RT809F software and press Write. Again, if it doesn't work on the first try or freezes, you should try again directly: select IT8XXX_ISP, open the file to load, press Write, power up the motherboard, and wait for it to enter ISP and burn the file to the new KBC. Here are some photos of the work done.
Attached Files
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