Need help please pcb problem

[Admin]

hello, long timer lurker first time poster, but anyways, i was installing a spider turbo and it would not work it ended up metering the fet pins and found that where the orange n-chan fet 1 wire connects to there is no langer a ground there. i figure for sure this is the problem and that i probably over heated it when soldering to it. does anyone know a solution to this such as what that pin connects to so i can just tap there or if i can some how fix it? it is not black and still looks fine just doesnt have a ground signal. oh yeah it is an xmod evo by the way. thanks in advance to any helpful info.

[klims]

don’t quite understand what “metering” means but i have noticed that the 7317 FET’s seem to keep their last gate signal, as in if you turned them on then disconnected the wires they would stay on and would sometimes change state while soldering. i never worked out why but the mosfets still worked afterwards so i don’t think thats your problem.

for a bit of troubleshooting you should make sure you have connectivity from the board all the way up to the gates on the FET’s (pin 4). if thats not your problem then make sure all the wires are soldered to the right pads, and if that doesn’t solve it then try turning the car on for a second and only a second! if you have wired it incorrectly you could blow up the FET’s. make sure the RX is on and then turn the car on the steering kicks to the centre. this will let you know if you have power to the PCB. if it doesn’t react then maybe you should check that its all hooked up right.

i should mention that i have a mini z, but i think it should all work the same.

Andrew.

[Admin]

metering as in using a digital multi meter to test for voltage. the pcb is fine in that steering and lights still work its just that there isnt a ground signal at the fet pin when there should be. i actually double checked this on a buddies evo xmod. i wish i could link a picture of the pin i am talking about but i am at work and the computers here suck and i cant load pdfs to get to the pic 🙁

[Admin]

k here is a pic from the “spider” install guide. the circled pin no longer has a ground signal when it should and i think it is because i heated it to much and this is what i need to know if is possible to fix

[klims]

do you mean the pad is no longer at 0v? GND and 0v can be different…
that pad should change from 0v when the motor is not spinning to 3v when the motor is supposed to be spinning if i remember correctly (may be 3v when in reveserse).

[Admin]

all the other pins on the n chan side read as a ground except that one and all the pins on the p chan side read 5 volts whether i am pulling the trigger or not. and on my buddies xmod it has a ground on the pin that mine does not and his xmod works and mine does not so i assume this is the problem

[klims]

if you are not getting a zero on that pin when the trigger is off, and not getting a high when the trigger is on (forward or reverse) then this is a problem.

try follow the track and see if you can take a test point from another place.
this will help you to find out if you have fried the track.

sorry dude but i don’t actually have an xmods so i might not be the most help

Andrew.

[Admin]

thats what i need to know, is where the track goes. i tried to do a continuity test on my buddies xmod and couldnt find where it connects to. im just hoping someone knows and can point me in the right direction.

[Admin]

bumpizzle!

[Admin]

nevermind i figured it out it is the small resister between the fets. thanks for trying to help klims

[Aaron]

Yeah, Klims is right the FETs change state when you try to check resistance etc through them. The only way to really test them is to use a “Transistor” tester that works with MOSFETs. It has to be done out of circuit and honestly I think it’s just easier to replace them.

A.

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Site Owner Guy.

[klims]

man i wish someone had told me that one. for 2 days i thought i was going mental because my circuit want’ working and i couldnt’ even test for continuity! does anyone know why they do that? and to add to the mystery it seems to be only the SO-8 package that does it. i have some mosfets in a D2-PAK package and they are sweet.

[Aaron]

Different MOSFETs all behave differently. The ones we use for the Mini-Z just seem to trigger and behave like that while some don’t. Years ago I made a thing called an “in circuit transistor tester” and it also worked for most MOSFETs – I have to replace it as it died about 4 years ago, but one of my multi-meters can do it out of circuit so I’ve nto had a mega need.

A.

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Site Owner Guy.

[Author]

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