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Transistor replacement soldering question

I share your concern, I bought Vershay 1/2 W that looks more like 1/8W. I don't know whether that matters as I am not a component expert ( this is Conrad's department). All I can say is I did not use them. I order other brand......AND I checked the dimension before I order them.
 
the blue resistor looks more like 1 watts compared to the small ones. Now, the 4.7 ohms have an exclamation mark om a trangle with them in the schematic. This is meaning something, which probably designates it to be an inflammable or fusible one....So look in the manual what it means.
 
gslikker said:
the blue resistor looks more like 1 watts compared to the small ones. Now, the 4.7 ohms have an exclamation mark om a trangle with them in the schematic. This is meaning something, which probably designates it to be an inflammable or fusible one....So look in the manual what it means.
Click to expand...

In the schematic the resistors are marked as 4R7F
19048592_10154582619372551_1577089501_o_zps3a7kdzsv.jpg


From below description its supposed to be a "safety critical" part, a fusible resistor 4.7 OHM and, carbon film, 1/4 Watt unless otherwise is specified.

My new resistors probably not "fusible" then ??

19047266_10154582600472551_1094529765_o_zpssnff4khi.jpg


Thanks
KO
 
Probably not, but you should choose 'flame proof' types to replace fusibles. Hardly anyone bothers with new fusibles, most replace with flame proof metal films - I certainly do. I just make sure the new resistors are set away from the board so if they do burn, they don't burn the board as well.
 
On second thoughts, you might be able to use those small resistors. In normal operating condition you have less than 10mA going through. Even a 1/8 resistor is not going to burn. It really serves as a fuse in case the output got shorted out and draw heavy current, then it draw enough base current to burn the resistor. Chances are your output transistor burned and burn the resistors along with it.

I don't like that they use resistor as fuse, in my design, I put a 5A fuse on each rail on the pcb, so if anything happens, the fuse will be the first to go. It did on me when I was testing, I shorted the output and popped both fuses, everything else is A ok. Just change the fuses and on with the testing.
 
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