How to Troubleshoot a Varistor
- 1). Turn off your equipment and unplug it from the AC power line. Allow 15 minutes for the equipment's capacitors to discharge.
- 2). Open the equipment cover or case with a screwdriver. Set the screws and cover aside in a safe place.
- 3). Locate the opening where the power cord enters the equipment case. Trace the wires back to the power switch, fuse holder and power supply.
- 4). Locate the varistor. If your equipment has one, it will be wired in series to the fuse holder and in parallel to the power supply. It may be a bright blue, red or yellow disk-shaped device the size of a coin.
- 5). Inspect the varistor for cracks, burn marks or other damage. If the varistor appears undamaged, proceed to the next step. Otherwise, replace it.
- 6). Heat one varistor lead with the soldering iron just enough to melt the solder. Draw the solder off with the desoldering pump. Gently work the lead free with the long-nose pliers.
- 7). Turn the multimeter on and set it to read "Resistance." If the meter has several resistance ranges, set it to "ohms x 100" or a low resistance range.
- 8). Touch one meter probe tip to each varistor lead. Read the resistance on the meter. If it reads very high or infinite ohms, the varistor is good. If it reads a few ohms or less, replace the varistor.
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