Back-UPS Pro 500 - Model BP500UC overload

[mjdemaio]

My old BP500UC is throwing the overload indication with nothing connected and a new fully charged battery.

There are no obvious bad components based on visual inspection. Based on some online searches for a similar unit (BP500I), I suspect a problem with the -8 volt rail - possibly a 22uF cap gone bad. Is there any way I can get a schematic for this older unit so I can troubleshoot it?

The circuit board is identified as 640-0236D-04.

[Teken]

APC / SE does not provide any public facing schematics to its customers.

Any you find on the internet have been leaked by third party repair facilities or reverse engineered and documented for public consumption.

From a practical standpoint it would be better to replace this ancient unit with a new one that uses better technology such a pure sine wave vs PWM.

Regardless, if your intent on repairing this device then metering out the individual components is the first step. The vast majority of time you’ll find one or more capacitors that are out of tolerances as such having the proper tools to measure ESR is imperative vs Capacitance.

Given the age, it makes little sense to ever replace just a single capacitor vs all of them. Other common failure modes are diodes, transistors, and power regulators.

In rare cases you may find one or more resistors that are out of specification / tolerances.

If a unit failed after a surge event the focus should absolutely be on the SPD circuitry such as MOV’S, GDT, etc.

Basic tests can be done in circuit while others must be done out of circuit without expansive testing equipment or knowledge.

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[mjdemaio]

Thanks, last night I did measure some caps in circuit and at least 4 of the 22uF caps are out of spec. I'll try replacing them with 105C equivalents with low ESR. I understand this unit is old technology. It has not been used for my primary computing resources for some time. I do have another pure sine wave unit for that.

Thanks again for you insight.

[Teken]

Let us know how things work out if you decide to pursue this repair and which specific capacitor is the main culprit.

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