Question about APC Back-UPS CS 500 VA Refurbished (BK500REFURB) UPS System

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Liebert UPStation S floating neutral failure

Hi, I have a Liebert UPStation S 4.5kVA, manufacture date 1994. The neutral of the 240 split phase input broke. When the UPS came up, it first complained that the input Hz was out of spec. By the time I got to the LCD entry that told me the input Hz was 0, the damage had been done. I smelled the magic smoke. When I opened the box, the analog control board had a smoked component, probably a 1-5 watt resistor from the look of it, can't see the silk screen due to the burn residue (I can send a picture). I repaired the neutral in the feed wire, but no joy. The unit will get through the self test, ask to press "ON" to start. I press "ON" and the unit will do another 5 sec inverter test, go to the "Normal" screen with loads operating, run another 3 or so seconds, then click off and put up the "Press ON to start" message again. No alert messages are logged as the machine cycles through the above steps.

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Surprised it tried to start with amissing neutral,
this is used to reference one side of the incoming live for the control circuits
Emerson do not release diagrams, and I doubt if anybody has the correct diagram as the unit is so old. ups is really difficult to repair, even with diagrams.
I used to fix AP200 series units and I had the service manuals, they were still very difficult.

looks like your ups is toast, could be expensive but,
maybe you can find a repair tech who can get parts form other units.

Posted on Sep 15, 2009


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