HP Scanjet 3970 Scanner
The fuse is there to protect the scanner's circuitry in the case that the 12V, 1.25A power source, the transformer, adapter, wall wart, or whatever you wish to call it, goes above the rated values. No higher or lower V or A should make it into the device in order for it to operate within its designed range and fail. Usually there is a slight surge of some sort that blows the fuse caused by a lightening strike near by, static, or any # of other possibilities. The adapter itself is usually weakened over time, rather than the source of this increase.
When the adapter goes too low, the scanner will not operate properly and usually windows will stop recognizing it as a usb scanner. At this point the various scanners on the market will give various different reactions that you'll see described in other problems in this forum, but they are all related to a reduction of the input to the scanner resulting in insufficient or erroneous output signals to the computer and windows various responses.
Although the fuse is the first point of protection of the scanner circuitry, it isn't needed most of the time if you use a good surge protector to prevent any extraneous voltages from getting into the adapter in the first place.
In other words, the surge protector is a 'fuse' for the adaptor, and subsequently, the scanner itself.
So my recommendation for those who have equipment that is normally much more difficult and expensive to repair properly, such as a soldered-in, blown fuse (which would be professionally repaired by replacing the entire circuit board rather than just the fuse), is to bypass the fuse with a piece of wire soldered between the two metal end-caps across the top; a very simple, very quick solution. Then use a good surge protector as your 'fuse' to protect the scanner's circuitry.
The obvious caveat is that you are taking responsibility for disabling the protection that was originally designed into the scanner to keep the delicate circuitry from failing due to extraneous voltage surges. There is very little risk of fire, but 100% risk of having to have the very same circuit board replaced or buy a new scanner.
Oct 31, 2007 |
HP ScanJet 3970 Flatbed Scanner