Need help with Brother sewing machine circuit board (I'm lost)

[ollihd]

Hi all,

I’m in desperate need of help solving the issue with this board. It’s the main board of a Brother 4000d sewing machine. The problem is that the embroidery units X pulse motor is not working. Machine gives out an error ”X-PM”. All of the pulse motors on the board are controlled by individual MTD2033G chips. All together there are 10 of them. When I first inspected the board, the chip connected to the X pulse motor was cracked so I changed it to a new one. Still nothing. I have changed all the caps associated with the chip connect to the X pulse motor, but it’s not working. By all I mean one electrolytic on the top + the smd one after it and two smd ones in the bottom of the board.

On the attached pictures I have circled the MTD2033G associated with the X pulse motor and the connector where the power comes in.
It seems like the MTD2033G associated with the X pulse motor is not getting power for some reason. Vcc from the power connector shows continuity to the Vcc of the chip. I know that the MTD2033G of the X pulse motor is not getting power since it's the only one of the 10 chips that doesn't heat up (viewed from a thermal camera).

I have also visually inspected the whole board and nothing seems to be out of place / burnt.

I can see that in the past someone has done a repair job on the wire leading to the front panel of the unit. Seems like the connector was broken and he/she soldered the leads directly to the board. I have also inspected that and it seems to be fine (and the panel works).

Any suggestions on what to check / start checking would be greatly appreciated. This is driving me crazy.
Obviously, I have no schematics for the board ☹

Front side of the board: https://holdfastholding.fi/temp/brother_board_top.png
Bottom side of the board: https://holdfastholding.fi/temp/brother_board_top.png

[ollihd]

Oh yeah, and C12 and C13 are missing from the pictures, they have also been changed to new ones.

[fzabkar]

Could the replacement part be a fake? Datasheet attached.

[ollihd]

I actually considered this, but it seems to measure just as the others beside it on the board.

[ollihd]

Actually ordered two of them and have tried them both.

[kripton2035]

are the two power resistors of that chip around the same values that the other resistors ?
do you have any scope to look at the signals of that chip and compare to the others ?
can you upload the thermal picture of the unit ?

[fzabkar]

This is the URL for the bottom of the PCB:

https://holdfastholding.fi/temp/brother_board_bottom.png

Are the charge pump capacitors charged (pins 15, 16, 17)?

What are the ENA A & B and PHA A & B pins doing?

Is the Standby (STB) pin low (Standby mode) or high (Active mode)?

What current is being selected by the I0 and I1 pins? Are both pins high (= 0 current)?

Are both Vmm (motor supply) and Vcc (logic supply) present?

[ollihd]

are the two power resistors of that chip around the same values that the other resistors ?

Exact same values as the others.

do you have any scope to look at the signals of that chip and compare to the others ?

I do, and I can!

can you upload the thermal picture of the unit ?

Just a second, I'll take a few pictures and upload.

[ollihd]

Some thermal images from the top and bottom.

https://holdfastholding.fi/temp/brother_4000d_thermal.rar

A0049_IR.JPG = From the bottom right : 1st chip is for threading motor, second is for Y pulse motor and the third (cold) is for the X pulse motor. The very last one on the most left (cold) is for the thread guide motor and does work when thread guide is activated in the machine. The Y pulse motor also works and is warm from the start.

[kripton2035]

as the X and Y motors circuits must be close to same, did you try to swap the motors to see if the chip is working with the other motor or not ?

[ollihd]

Thanks for the suggestion, tried that and both motors work.

I did some measurements on the X pulse motor controller chip and it gave me the following:
VCC = -5V
OUT1 = -6V
OUT2 = -5V
OUT 3 = 0
OUT 4 = 0
VmmA = -26V
VmmB = -26V

Measurements from the Y pulse motor chip:
VCC = -5V
OUT 1 = -27V
OUT 2 = -27V
OUT 3 = -27V
OUT 4 = -27V
VmmA = -26V
VmmB = -26V

I also TOTALLY messed up and shorted the PHA B and ENA B legs together and now I have another problem somewhere.... machine won't turn on anymore. Checked the power circuit fuses and they are all intact. Fast visual inspection showed nothing blown. Have to solve this now first... damn...

[ollihd]

Yeah... going deeper... now I can't find what causing the machine not to work after shorting the two pins...