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[Tutorial] Realteus Forcefeel Pad Repair tutorial and some notes


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First of all I'm not an electronics engineer so if you have found some inaccuracies please correct me, thanks.

 

There is a recurring problem with damage of the two TPL7407L motor drivers used in Forcefeel. First one drives motor number 1 and a RGB diode and second one is driving motors number 2-8. I looked up the datasheet of TPL7407L and I found that there are some design problems in Forcefeel but I'm not sure what is causing chip damage. Assuming overcurrent for now.

So do not overuse control panel motor testing on 100% for extended periods of time. If you have to - do it one by one for short periods of time.

 

  • Realteus didn't use a schottky diode on pin OUT7 to protect the device from negative transients from inductive load as described in datasheet 8.2.1.
  • There should be shorts between GND and unconnected input pins as stated in 8.2.2.1 but that's not so essential - its just bad engineering.
  • I measured current flowing through the motor number 2 on (control panel 100%) and there was steady ~100mA - so it's within specifications. Motors number 3 and 4 are a little different/faster than others (I didn't measure them). Maybe there are some bigger numbers in the current flow.
  • As of Figure 5 and 6 in the datasheet there should be enough headroom on the chip loaded with 7 motors with 100% duty cycle - about 160mA-220mA per motor
  • Cables inside pads are scrambled under the motors. It can have an impact on longevity.
  • They didn't balance the load between two TPLs which is another case of bad engineering.

 

To repair You should desolder faulty TPL7407L motor driver and solder a new one. I would suggest buying a better TPL7407LA version (with LA). This is a pin-to-pin replacement of the TPL7407L with more robust operation and it does not need a Schottky diode. You need to buy the TPL7407LA SOIC-16. Do not buy the TSSOP version - it will not fit.

If motor 1 and diode works then you should desolder only the second chip which drives motors 2-8 and vice versa. 

 

To do it properly you need a couple of things. 
If you don’t have some of them DO NOT START REPAIR. Only proper tools will make it easy. If not You will probably kill/overheat a PCB. If you will do it as described it will be a painless and satisfactory process. Maybe you will use it again somewhere else who knows?

 

You will need:

  1. Heat iron with adjustable temperature - do not use one without it (any cheap chinese will do like WEP/ YIHUA etc)
  2. Hot air gun with adjustable temperature - again - do not use one without it (any cheap chinese will do like WEP/ YIHUA etc )
  3. Desoldering wire - small width 2-3mm (if you're from a country which doesn't do metric - sorry I don’t care 🙂
  4. Tin-Lead solder 0.5mm diameter - I mean it - Lead solder not factory used unleaded ones. It should be SnPb.
  5. Flux like AMTECH NC-559-ASM-UV sold in syringes - very handy You will use it a lot
  6. Pure Isopropanol Alcohol 99% Isopropyl Liquid Cleaner IPA - to clean this mess up after soldering with some old toothbrush or some ESD-safe brush. You can fill/use an atomizer/sprayer and fill Isopropanol in it. 
  7. Tweezers
  8. Kapton tape to secure plastics around
  9. Aliexpress and ebay are your friend, you won’t regret getting proper tools believe me. They can be cheap chinese ones - you’re not a Mozart of electronics. More like Justin bieber


Desoldering/ soldering advice

  • Pro-tip - before desoldering put a small amount of flux around chip legs, heat the iron, add some tin to the tip of iron and move right and left around chip legs and repeat - to mix factory unleaded tin on legs with your easier to manage leaded tin. This will make a big difference while desoldering. Then start desoldering with a Hot Air gun.
  • When the chip is desoldered it will become extremely loose like on ice so be prepared. Just gently push it while you heat it up with air. 
  • Remember you’re heating everything up there on PCB so it’s possible you will heat up some resistors or caps - it’s normal. Plan before and do a dry practice on how and where you will move the chip and how you will pick it up. When you pick it up you will drop it, believe me. Plan accordingly. Do not move it to those resistors around just slide it to some empty place - remember it will be loose like on ice. Prepare where you will put the air gun so you won’t burn your sh.it trying to pick up the chip juggling an air gun in second hand and fry your balls...
  • Clean pads with iron, flux and wire before soldering.
  • Hot Air should be VERY hot and close to the chip. Remember your plan is not to cook the chip and PCB for 2 minutes and make it crispy and crunchy. Your plan is to get in fast and get out 

 

 

forcefeel cable cheatsheet.png

 

 


Look up on youtube some guys who do it often like this one 

Desoldering 

 

 

Soldering 

 

 

 

 

 

 

 


Do not pick up chip too early when it is not completely desoldered because you will rip pcb pads. Do not do like this bone.head

This is how NOT TO DO IT. He is ripping it off the PCB

 

 

 

 


Have FUN and don’t burn your ass!


Edited by soundslikerust
  • Like 1

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Appreciated the effort and time sir, very detailed task. 

How do you check the motors, with the test function? 

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Just run control panel 75% of power and turn ON/OFF every motor one by one. You will know which ones work/do not work and replace faulty TPL chip for a better one TPL7407LA Schottky diode version (with LA). Like I said the root cause of the damage is still unknown.

If you want to check motor currents you'll need amperemeter plugged in series in line with motor. Obviously you have to disconnect a wire at some point to do it so choose best place to do it (I did it near motor).

I don't think you have to measure current anyway - it's just in case you want to investigate thing further only

 

EDIT: corrected TPL model for LA


Edited by soundslikerust
  • Like 1

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