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Topic: Help identifying resistor/capacitor to replace on servo mg996r pcb  (Read 1 time) previous topic - next topic

Slaghton

I'm looking to replace a resistor and capacitor on a pcb board with the AA51880 control circuit made from AgaMem Microelectronics. The reason for swapping out a resistor and capacitor is to improve the dead band/performance of the servo.  I also got another capacitor to go across the motor terminals to reduce motor noise.

http://datasheet.eeworld.com.cn/pdf/ETC/24676_AA51880.pdf

I need to replace R3, the dead band timing resistor, with a 1K/0603 resistor.  I have a decent idea which one it is but i'm not to experienced in reading schematics.

Also C4, the dead band filter capacitor, should be replaced with a 100nF/0805 or 0603 ceramic capacitor.

I included a picture that has the front and the back of the pcb board.

Thanks for anyone's time that takes a look at this.


http://i175.photobucket.com/albums/w137/sk8er754/AA51880%20Jpeg_zpsktqkqnqp.jpg

*Photobucket and attached img are the same*


Southpark

Should be straight forward to find that resistor R3.

The circuit diagram reckons that one side of R3 is connected to pin 11 of your chip.

So pin 1 of your chip is bottom-left side of your photo. Then bottom right side will be pin 8.

So pin 11 should be the third pin from the upper-right side. If you get a multimeter and locate all the black-coloured resistors, then measure the resistance between pin 11 and each of the resistor terminals. If you get a very low ohm reading between pin 11 and one particular terminal of a black coloured resistor.... then that component will be R3.

Slaghton

Ah thanks for the tip!  I'll have a go at it this morning and see what I come up with. 

Slaghton

Should be straight forward to find that resistor R3.

The circuit diagram reckons that one side of R3 is connected to pin 11 of your chip.

So pin 1 of your chip is bottom-left side of your photo. Then bottom right side will be pin 8.

So pin 11 should be the third pin from the upper-right side. If you get a multimeter and locate all the black-coloured resistors, then measure the resistance between pin 11 and each of the resistor terminals. If you get a very low ohm reading between pin 11 and one particular terminal of a black coloured resistor.... then that component will be R3.

Oh, it appears the resistor on the right (272) is what gives the very low ohm reading on the side closest to the chip.  Looks like that is the one to replace with the 1k resistor.  Now i just have to locate the capacitor to replace and im good to go but I think I can get results with just swapping the resistor for now.

Southpark

Nice work. For the capacitor, try to trace the capacitor in a similar way. For example, of the capacitor is meant to be connected to the other terminal of the R3 capacitor, then use the meter to measure resistance between that terminal and other capacitors. C4 will be the only capacitor connected to the 'other' terminal of R3. Also, 1 side of C4 will be connected to ground, so that side will have a low resistance between itself and a ground terminal. And ground terminals are pin 12 and pin 13.

Pin 1 is the pin on the chip that has the indented divot (dot) on the chip. From that pin 1, the other pins (2, 3, 4, etc) go around the chip in anti-clockwise direction.

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