Revisiting The BX1000
I was generally impressed by the build and component quality that went into APC's 10-year-old APC BX1000. Little did I know I'd be writing a repair story about it two years later.
If there's something you should have learned about me by now, it's that I despise hardware the manufacturer cut corners to make. Also, I hate giving up on what should still be usable hardware. When my BX1000 failed in December 2015, despite what appeared to be great design and execution, I was surprised. I cracked it open and couldn’t find anything visually wrong with it. Quick spot-checks failed to reveal anything obvious. So, I bought the Cyber Power LX1500 and tossed the BX1000 in my “fix it later” pile. After nine months of hunting down lower-end to mid-range alternatives, tearing them down and being repeatedly disappointed by their quality, I decided it'd be a good time to revisit the APC unit for a more serious attempt at UPS necromancy.
What symptoms did my BX1000 present back then? A picture is worth a thousand words, so I’ll let this short video tell the story before I go into more depth:
The clicking did not start quite so bad. It began around October 2015, coincidentally when the landlord turned the electric boiler back on. The UPS responded with a few clicks each time the boiler and its pump kicked on. I measured line voltage and found it to dip as low as 107V on cold nights, so I initially shrugged it off as the boiler start-up dragging line voltage low enough to make the UPS’ voltage regulation kick in.
It got progressively worse from there until December, when every minor line voltage fluctuation caused the UPS to go into a clicking frenzy, occasionally followed by the UPS switching to battery backup for an increasingly long time, and then going back to line power. Checking AC voltage with my oscilloscope revealed nothing to explain the UPS’ behavior, and probing its output showed that the clicking happened to be the AVR transformer getting switched in and out of boost mode, which was consistent with the line voltage sags I measured previously. By the time I retired the BX1000, it would no longer reliably power up while connected to AC power. When it did, it took forever for the UPS to switch back to line power, even when my instrumentation said the input looked perfectly fine.
What could cause a UPS to fail in this manner? Mainly, I suspected bad power delivery to the circuitry managing input voltage detection, loss of power or bad power at the UPS micro-controller, or a loss of filtering at the detection circuitry’s inputs causing it to trip on input noise. I don't know how line voltage monitoring issues could be related to the UPS failing to start, but perhaps we'll find out.
Since everything appears functional, aside from the erratic behavior, I am optimistic that today's exploration will end with a simple, definitive fix.
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That's one aspect that sooo many folks never consider or can't be bothered to investigate. Just like a fuse that keeps blowing...there is something that's causing it to blow...even if it lasts a while before blowing. Even worse is when they decide to bridge it with a piece of wire or wrap the blown (glass) fuse with aluminum foil. Now I'm guilty as well but ONLY long enuff to get myself out of a jam...like being stranded on the side of the road or something. Just never do it with a high current load or if it's blowing the instant you turn it on...and never with a sensitive/expensive critical component like the ignition ECU of your self semi-restored muscle car project...don't ask.
Too much credit :) This is basic troubleshooting, anyone going through electronics tech training should be able to do as before graduation.
Where did you manage to get the replacement pieces? Where could I find the micro-controller for this unit or how should I identify its part number in order to look for it?
For the micro-controller, I didn't touch it. Even if I had wanted to replace it, they can only be ordered blank from parts distributors (or pre-programmed with your own firmware for large enough orders or distributors that offer such a service for an additional fee) and those would be no good without the correct firmware to put on them. If the controller died, it is game over unless you can find a donor UPS based on the same PCB.
P.S. This review has also shown us the importance/need for UPSs reviews. Since PSUs are being thoroughly reviewed for many years, i don't understand why UPSs shouldn't be reviewed as well!! A PSU's proper operation is in consequence with the proper operation of the hardware that "feeds" a PSU (*UPS)
P.S.2 : Great article by the way!!