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Power Supply Repair
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patrickoneal:
I have an automotive wheel balancer that is throwing error codes for low vcc very often. I tried to balance a wheel on it, and sometime during the balancing process the machine always craps out and gives a low vcc code, usually after the 230v electric motor runs, but sometimes when the machine is just sitting idle. I don't have an ESR meter, but I did check the motor start and run caps with my fluke 87 and the capacitance is is dead on for those, so I don't think it's some huge inrush from the electric motor causing issues. I've also seen a high VCC code just once. The code for VCC too low is for voltage under 5.10V, and too high is over 5.35V.

The motherboard for the machine is situated on a larger power circuit board. This board contains controls to start and stop the electric motor and what looks to be a switching power supply to supply VCC to the motherboard. None of the capacitors outwardly look bad, but they're 15 years old, so I'm suspect of the caps in the 5V power supply section.

I physically measured the caps and noted the values and ordered replacements from digikey. Before I ordered, I read that low esr caps are a good thing in a power supply. Out of the 6 capacitors, I could only find the 3 on the right side of the photo in the low esr variety at digikey(1200uf x2, and the 560uf). I believe these are the output filtering caps. For the remaining three I could only find general purpose caps and the quoted ESR is quite high. I don't think that's an issue on the large 120uf 400V cap, but I'm not sure of the other two(the 33uf and the 47uf). The 47uf might have been a lower voltage than 63, but that was the closest I could find.

Two questions:

Do you think I'm on the right track to stabilize the power supply?

Do you think the general purpose caps are fine for the 120uf, 33uf, and 47uf?

Thanks for any help.
patrickoneal:
The closest component to the 47uf cap, under my red arrow, is a TI TL431C: http://www.ti.com/lit/ds/symlink/tl431.pdf

The component under the black heatsink near the right side is a B1545 Schottky rectifier.

The component under the silver heatsink is unknown, because the heatsink is soldered to the board.

There is an optocoupler near what I assume is the transformer.
t1d:
As for suspecting the power supply... Given the errors, sure, that's not a bad place to start looking.

I take it that the controls are built directly onto the balancer. If so, it is subject to a lot of vibration.

Vibration doesn't have to have a large amplitude, to be destructive. It just has to hit the wrong frequency. At that frequency, the shaking is most intense.

So why talk about vibration? Because I might suspect a broken solder joint, or a cracked PCB. Do a close, visual inspection, with magnification and light. Use a non-conductive stick, to gentle push on things... Reflowing all the joints, just because, may be just as easy.

As for caps... Suspecting 15 year old caps is certainly prudent. Whether, or not, they are the problem, replacing them, while you have things apart, makes sense.

Looking for visual indications that a cap has failed is the first place to start. But, caps can, and do, fail, with no visual indication. They dry out, or their ESR value fails.

This type of cheap ESR meter will find hidden cap failures and actually has a decent reputation . I have one and I love it. Look for the newest technology and firmware and the best price. https://www.ebay.com/itm/LCR-T4-Mega328-Transistor-Tester-Diode-Triode-Capacitance-ESR-Meter-W-Shell-US/302739677139?epid=15003944572&hash=item467cb0dfd3:rk:5:pf:0

As for low ESR caps... If Digikey doesn't have what you want/need, then don't be afraid to go to multiple vendors, to get the right stuff. I like Mouser.com.

Yes, you will pay multiple shipping costs. But, you can write that off, as a cost of repair and for the sake of the value of the machine. In other words, it is just plain worth it.

Good job, on getting the cap measurements. When that step gets missed, things don't fit.

Is anything getting warm? Apply isopropyl alcohol and watch the shine, to see what dries out first. This is will be a hot spot. Heat can be an indication, of a problem.
FriedMule:
Is it possible to desolder the component under the  the silver heatsink without removing it, so you can test what component it is?
I would choose some good general purpose caps like Panasonic and when mounting them, give them a "bath" in hot glue, to minimize vibration damage in the future.
patrickoneal:
Thanks guys.

The 3 low ESR caps I was able to order from digikey for what I believe are for the output of the power supply are from United Chemi-Con and they're automotive grade. I figured rightly or wrongly that they would be good on a machine that moves around quite a bit. I think low ESR is appropriate for the application.

As for the two small caps, I ordered these, but didn't notice that the high ESR was rated at 120Hz rather than 120KHz. Does ESR rise or fall with frequency? These are the two parts, no big loss if they go in the trash:

https://www.digikey.com/product-detail/en/illinois-capacitor/336CKE063M/1572-1125-ND/5344055
https://www.digikey.com/product-detail/en/illinois-capacitor/476CKH063M/1572-1476-ND/5412774

For the 400v cap, which I'm guessing is the input filter, I order this one, and I believe low ESR isn't a concern for this application, so hopefully it's fine:

https://www.digikey.com/product-detail/en/panasonic-electronic-components/ECO-S2GB121BA/P10138-ND/262200

Also, thanks to t1d for the isopropyl suggestion, I'd never heard of doing that.

I'll definitely checked for cracked or melted solder joints as well. I've ran into that before and it can definitely cause some serious headaches.

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