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OT: Tennis ball machine PCB testing

Hobonickel

Plastic
Joined
Feb 5, 2024
Location
Sandhills/Pee dee area
I am attempting to diagnose a PCB board from a tennisball machine. The machine was used only a handful of times (no more than 10) and my nephew loaded the hopper too full which put strain on the motor this leading to the pcb board being shorted. The company knows what the problem is because they immediately told me to remove the PCB and send it in at a cost of $150 dollars they will diagnose it fix (more than likely for added fee) and send it back. The machine is no longer under warranty and so I was first going to try and find the short on the PCB board.
The PCB board controls the function of the machine motors and it was unresponsive to any and all inputs. The leds on board seemed to be working so board was getting power. I have tested all the motors and they work fine ...for note the board has a remote and the remote also did not have any effect. Seems to be short on board itself. How does a locked motor (not turning freely or under resistance) effect or short a PCB board? ...Any ideas or guesses at what components I can look for and test on the PCB?? ... Any help is obviously greatly appreciated as I'm excited to learn how to do this basic troubleshooting.. I recently taught myself how to remove and solder in components (so I'm a complete newb) but the testing and diagnostic can be a little more confusing..I not lagging in motivation though and I have purchased a middle of the road auto dm. I want to see if I can find the short myself and level up.
thanks .. And I'm grateful for any advice I can get that leads to me circumventing this company's planned obsolescence and obvious extortion (always in jest)
Thanks
 
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The motor locking up draws extra current. The components in the power circuit on the board are rated to run the motor at a certain current. If it goes too far over that for too long, the magic smoke is generally let out of the bottle on circuit boards that have no protection for such an eventuality. I would start at the power input and work my way forward from there. There may be a "crowbar" type protection on the board that is basically the weak link in such an event. If that's the case, you might be able to just replace that, or it might have gotten by there also and toasted some other stuff. Common failure points are those "crowbar" devices, rectifiers and BJTs.

Also, you need to read the posting guidelines:


This post is fine here since you're trying to solve a problem, but it needs an "OT" tag in front of the title. Additionally, I'm going to move this to the electrical section where it's a better fit.
 
The motor locking up draws extra current. The components in the power circuit on the board are rated to run the motor at a certain current. If it goes too far over that for too long, the magic smoke is generally let out of the bottle on circuit boards that have no protection for such an eventuality. I would start at the power input and work my way forward from there. There may be a "crowbar" type protection on the board that is basically the weak link in such an event. If that's the case, you might be able to just replace that, or it might have gotten by there also and toasted some other stuff. Common failure points are those "crowbar" devices, rectifiers and BJTs.

Also, you need to read the posting guidelines:


This post is fine here since you're trying to solve a problem, but it needs an "OT" tag in front of the title. Additionally, I'm going to move this to the electrical section where it's a better fit.
much thanks .. I'll work thru the stuff you mentioned.. already great help and I appreciate it.. (I gotta get back to 3d printing these tennis balls .. tips hat to Donkey Hotey) lol)
 
These machines may have a motor that runs all the time, and the rest of the machine feeds a ball when told to. If this machine is of that type, does that motor run?

Other thoughts:

Find the wires to the board from the motors.

Follow the wires back to the PCB. One wire will lead to the power supply. Probably there will be a DC supply for any reasonably current unit.

I question the "short" as a diagnosis.... it is not likely that it would work at all if there was a "short", unless a fuse blew.

Check for a fuse, as the fuse could just be open due to overcurrent. It might also be blown because there is a "short", of course.

The fuse might be on the input to the rectifier of the DC supply, so the rectifier may be damaged.

Most likely there is a DC supply for the motors, and another one (or a tap off of the motor supply), that powers the logic and control. If the lights are working, and showing what they should, then that logic supply is likely to be working at least partially.

The other wire will go to some sort of "switch device" on the PWB. Possibly an IGBT or a MOSFET, possibly an old type transistor or even a relay if the thing is old enough (or a triac if the motors are AC).

While it is possible that device is shorted on one or more motors, that would likely only make the motor run continuously. You can check with a meter by disconnecting the motor wire and reading resistance to (probably) common from the point you disconnected the wire from.

It is also possible that one of those devices failed open.... that is usually pretty obvious.

Look for any damaged component on the PCB.

A pic or two of the board (closeup) and motors would eliminate some possible problems from the discussion.....
 
Yes, I checked both the two variable speed motors and the two smaller motors (for rotating machine left or right) All motors work fine.. there was a slight smell of smoke when the hopper was ball overloaded .. the machine shut down and was able to power back on however input controls no longer worked including the second stage power (there's a main power toggle and the power button on the control board) It all runs off of large rechargeable 12v battery... I would definitely like to install a fuse once I am able to troubleshoot the problem
 
OK 12V battery, that simplifies matters a bit. No rectifier, for one thing.

A "large" 12V battery can probably smoke the entire PWB, since it can likely supply over 100A, so look for the fuse (s).

If fuse is blown, I suggest not replacing it right away. Look for damage, and start by checking resistance to common on load side of fuse (remove the fuse).
 
There are no fuses that can find ... there's a trip switch and I don't know why it didn't do anything to protect it. I speculating it only protects charging the battery since this is where the switch located.
On the PCB board
I did find a short in a hexfet IRS2204S. Initially leads looked a little discolored compared to the other 3 so I tested it and couldn't get a stable read on that one (the numbers were all over the place and it's only one that triggered the dmm to screech at me).. searching the ID on the component instantly brought me to a guy fixing a similar TB by the same company so I was able to learn a bit watching his video. Not sure if I am testing it correctly yet but I'm making progress or at least it feels like I'm making progress lol ...I'm definitely learning something lol
 
to be more specific .. it's a Silent Partner Quest Tennis ball Machine I've had for a few years but only used maybe 10 times ... worked great until kids overfilled it with about 150 balls 💪 lol
 
Top left as shown? That one (IRF 220 Mosfet) looks like it got hot enough to reflow the solder.

The top (and bottom) right ones are dual diodes. Not the devices I'd necessarily expect to fry, but it is possible, depending on how they are connected.

Good chance the diodes are across the motor load terminals. They conduct current when the mosfet switches off, but if connected as I expect, they would not be affected by excess current. Diodes of that sort are tough devices.

The current would however, possibly overheat the Mosfet, which looks as if that might have happened. Could just have been replaced, but if so, it was done very sloppily. There is some flux on the leads, so replacement might have been done. That does not mean it's good. The solder job replacing it may not have connected it well to the "heasink area" of the PCB, so it could have overheated in normal use.

As mentioned, though, a shorted mosfet would just turn the associated motor on.

If the diode across the motor shorted, then the Mosfet would turn on into a short circuit, and that would blow it if the fuse did not open very fast. Fast fuses are not commonly used in these sorts of products, they are expensive parts, so a shorted diode would be expected to pop the Mosfet.

Check all the parts. The diodes should be low resistance indicated one way from each lower terminal to the large case connection where it is soldered down. The other direction (reverse ohmmeter leads) ought to be high resistance if the motor and battery are not connected.

The mosfet should check open all ways except for the internal diode from right hand terminal to case where soldered down, which should conduct one way only. Again, disconnect motor and battery.

Because parts across other parts can be very confusing as to what is actually shorted, check for parts that may be across anything that seems shorted.
 
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Top left as shown? That one (IRF 220 Mosfet) looks like it got hot enough to reflow the solder.

The top (and bottom) right ones are dual diodes. Not the devices I'd necessarily expect to fry, but it is possible, depending on how they are connected.

Good chance the diodes are across the motor load terminals. They conduct current when the mosfet switches off, but if connected as I expect, they would not be affected by excess current. Diodes of that sort are tough devices.

The current would however, possibly overheat the Mosfet, which looks as if that might have happened. Could just have been replaced, but if so, it was done very sloppily. There is some flux on the leads, so replacement might have been done. That does not mean it's good. The solder job replacing it may not have connected it well to the "heasink area" of the PCB, so it could have overheated in normal use.

As mentioned, though, a shorted mosfet would just turn the associated motor on.

If the diode across the motor shorted, then the Mosfet would turn on into a short circuit, and that would blow it if the fuse did not open very fast. Fast fuses are not commonly used in these sorts of products, they are expensive parts, so a shorted diode would be expected to pop the Mosfet.

Check all the parts. The diodes should be low resistance indicated one way from each lower terminal to the large case connection where it is soldered down. The other direction (reverse ohmmeter leads) ought to be high resistance if the motor and battery are not connected.

The mosfet should check open all ways except for the internal diode from right hand terminal to case where soldered down, which should conduct one way only. Again, disconnect motor and battery.

Because parts across other parts can be very confusing as to what is actually shorted, check for parts that may be across anything that seems shorted.
I said top right .. but I meant to say top left ... yeah there were only two of the IFR and bothe on left .. yep it was that one on the left that looked bad close up... it was one of those days lol apologies
 
I'll rereview everything in here tomorrow... I kind of burnt out myself .. I appreciate all the Jedi level advice. I've never test anything on a PCB board until today. That was a brand new machine when I bought quite a few years ago... so that's straight from retail company. I wouldn't know what sloppy welds would look like on a pcb lol but doesn't surprise considering how they company want to charge me $200 to swap out a mosfet. Like I said they came off like they know exactly what's wrong as I told them the kids put too many balls in the top and putting a strain on the smaller motor that turns the top (it basically stirs the balls so they keep feeding and that more is really small id luv to replace it with something a little more robust if I can get past this hurdle
Thanks for all the great replies and tips!!! Can't begin to say how much I appreciate it... I'm gonna keep at it... worst case I get to learn electronics 101
Thanks Thanks 🙏
 
I am amazed people here (anywhere) can look at a board picture and identify the bad part with exact numbers.
Credit to y’all.
 








 
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