Electronics > Repair
Bosch driver board repair
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dark_hawk:
Hi,
I'm trying to repair this Bosch GSR 10,8 V-LI driver board, and I'm at my wits/knowledge's end.

https://www.boschtoolservice.com/de/de/bosch-pt/spareparts/akku-mittelgriffschrauber-gsr-10-8-v-li-3601J92U00

The fault is intermittent which is a bad fault to try to find. Sometimes the board works fine, other times it does not work at all, and other times it works at like half speed for the motor.
The machine does not have variable speed when holding the trigger half way, it's either on or off, disassembled the switch to make sure of that.

What I have been able to gather so far:

1- The IC TC1411NE is mosfet gate driver, pin 1 and 5 are Vin, Pin 4, 8 ground, pin 2 is the input, pins 6,7 are outputs, and pin 3 is NC.
When Pin 2 input has 4.2v, pins 6,7 (outputs) has 6 volts, so the gate of IRL7833 is at 6 volts and the motor is running at full speed.
When the gate is at zero volts the motor is off, but i've been able to measure volts ranging from 2.5-5v at the gate, the motor then is working slower, and mosfet and the double package diodes are getting hot.

2- Pin 2 (Input of the mosfet driver) is connected to pin 1 of an SMD SOT23-6 (marked V6 on the board) with a marking MA, and its the same voltage as pin 2 of the mosfet driver. I have no idea what that smd package is and what it does, my guess is that it gets some enable signal from somewhere and pin 1 gets pulled high to 4.2v which in turn enable the mosfet driver, just a guess though.

3- When shorting the input of the driver to any 6v rail, and motor runs at full speed no problem, remove the short, it's back to the original state, either not working or working at half speed.

4- Shorting R30 resistor (right side of the board) also makes the motor run at full speed no problem. The resistor value is correct out of board.

5- I've checked all diodes and capacitors on the board and all seem fine. Also checked most of the traces with no breakage in the traces I can see.

How do I proceed?

Thanks.
fzabkar:
MAx and A2x could be dual PNP and NPN transistors.

NST/NSV3904DXV6, Onsemi, dual NPN transistors, 40V, 200mA, marking MAx, SOT−23/SOT−323:
https://www.onsemi.com/pdf/datasheet/nst3904dxv6t1-d.pdf

NST3906DXV6T1, Onsemi, dual PNP transistors, -40V, -200mA, marking A2x, SOT−23/SOT−323:
https://www.onsemi.com/pdf/datasheet/nst3906dxv6t1-d.pdf

TC1411/TC1411N, Microchip, Inverting/Non-inverting, 1A High-Speed MOSFET Driver, 4.5V - 16Vin, 8-Pin MSOP/PDIP/SOIC:
https://ww1.microchip.com/downloads/en/DeviceDoc/20001390F.pdf

"8E527" in the SOT89 package appears to be a 3-terminal regulator. The marking is probably "8Eyww" (yww = Year/Week).

http://markingcodes.com/search/c/8e

IRL7833, International Rectifier, MOSFET, n-channel, 30V, 150A, 3.8mOhm RDSon, TO-220AB:
https://www.infineon.com/dgdl/irl7833pbf.pdf?fileId=5546d462533600a4015356600d71257b

I expect that the variable speed is achieved via PWM. That is, the motor current is being switched on and off rapidly. This means that you would be measuring the average voltage at the gate, not a constant voltage.
Circlotron:
Whoever did that board layout should be put in jail.
dark_hawk:

--- Quote from: Circlotron on June 21, 2024, 10:59:26 pm ---Whoever did that board layout should be put in jail.

--- End quote ---
I don't have any experience laying out boards, but It has to fit inside a relatively small enclosure and be a specific shape to be secure between the two halves.
I won't be too harsh on the one who did the layout.
dark_hawk:
What would be the purpose of the 224a Low-power quad operational amplifiers in a circuit like this?
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