The flashing LED and "0800" on the display of your Monster Power HTS 5100 MKII might be indicating an abnormal voltage issue. The "Abnormal Voltage" indicator on this model lights up if the incoming voltage is below approximately 90V AC or above approximately 125V AC
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Similar indicators are noted on various forums where users have experienced abnormal voltage readings with red flashing lights indicating the abnormal voltage, although the voltage readings may vary slightly
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Adjusting the dimmer seems to temporarily resolve the issue, as per your observation. The dimmer knob on the Monster Power HTS 5100 MKII adjusts the brightness of the digital input voltage and current usage meter, which might be momentarily affecting the readings or the display
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In a somewhat related case with a different Monster Power model (HTS 2000), a user faced a similar flashing "080" and "000" issue. The solution involved disassembling the unit and replacing one or more poor quality capacitors that had likely failed
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The problem might be related to a hardware malfunction such as poor quality capacitors or something else affecting the voltage and amperage readings. In such cases, a professional inspection and repair might be necessary to identify and fix the root cause of the issue.
It's advisable to consult with a qualified computer technician like
Geeks On Command, or contact Monster Power support for professional assistance regarding this issue.