Hi all,
Question about selecting a fuse if the SMD fuse marking has been blown off by the heat generated when the fuse blew.
I am repairing a QL 1100 NWB Thermal printer from Brother.
These have a Texas Instruments 54335A voltage buck converter on board. These are notorious for failing short, where the input pin is shorted to GND. I believe there is another post on EEVBlog that shows its failure in a Bose Speaker.
I have isolated the issue to the 54335A Buck converter on the board. On the Vin line, there is a fuse that links the Power Board's +25V input to the buck converter.
The buck converter's function is to produce 5V, which is used directly, and indirectly as 3.3V, both of which are for powering the microprocessors on the PCB. The +25V input also goes directly to the mechanical roller and thermal heating function.
On the board, the section marked for the 54335A reads: 50V, 2A
The fuse unfortunately is illegible. It is an SMD fuse and I think it is 0805 or 1206 size. What I can make of it suggests it might be a LittelFuse N or a P marking.
I've gone to the datasheets and this corresponds to a rating of 2A and 3A respectively. That seems to be consistent with the marking on the PCB itself.
Can someone shed light on guidelines on how to select a fuse? Anything else I need to consider? I don't want to over-rate a fuse and end up with current blowing my traces up.
Thank you