Eric Smith wrote: *Ever* is a rather strong statement! I've been known to "short out" fuses in troubleshooting boards with a higher rating fuse than is called for for troubleshooting purposes, and yes, even short them out with a jumper wire (although granted very rarely!) One example was a shorted chip that for whatever reason, I didn't find with the VOM. Running it a short time with the fuse shorted out heated up the chip and I was able to feel where the problem was. Troubleshooting vs normal operation :).

John Foust wrote: That is also a sometimmes useful method of finding where the problem resides. Chuck

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I wrote: Marvin replied: Not so bad if it was something common and easily replaceable. But how would you have felt if the problem had turned out to be a $0.05 shorted passive compenent which caused then caused the failure of a rare or exepnsive chip? Remember, the fuse isn't to protect the component that failed and caused the problem, it's to protect the rest of the components that are still OK (*). IMNSHO, it is almost criminally negligent to suggest shorting a fuse to anyone as a troubleshooting technique. There are several proper ways to diagnose problems like the one that you describe; typical is to use a current-limited lab power supply to operate the board at a lower than normal DC voltage and determine where the current is going. For AC equipment the equivlanent is to use a Variac (but remember that a Variac does not provide isolation, so you may need an isolation transformer as well). If you know there is a short on a board in a certain signal, but not where the short is physically located, a current tracer is quite an effective troubleshooting tool. I had to fix a board with a solder bridge on the component side of a board under a socket, and visual inspection didn't reveal which socket. Rather than removing all eight candidates (or as many as it took to visually spot the short), I was able to pinpoint it with a current tracer. I realize that not everyone owns lab supplies, Variacs, and current tracers. However, I would point out that not everyone should be troubleshooting faults in electronic equipment, either. Eric (*) The main purpose of fuses in consumer gear is actually simply to prevent the equipment from overheating and bursting into flames, or causing something else to burst into flames, or burning the user. But if that serves to protect valuable components as well, why should you voluntarily give up that protection?

Tony Duell wrote: I've lusted after the HP Current Tracer for years, but they are very expensive and the price keeps going up! Richard Ottosen has designed his own, which is fairly simple and inexpensive. That's what I used in the example I cited. I'll have to try to convince him sell them, offer a kit, or publish the plans. Eric

Eric Smith wrote: IMNSHO, there are many troubleshooting techniques, and part of being able to do effective troubleshooting is knowing when to use what technique. Like writing robust code, error checking is probably 80% of the code bulk (okay, slight overstatement) and when I talk about troubleshooting techniques, I leave out the disclaimers most of the time. I tend to assume that whoever trys them has the background to know when they are applicable. When I talk about shorting out a fuse, it is assumed that other common troubleshooting techniques have failed.