an amp of mine failed recently because external mains overvoltage. ok, I was reckless enough not to fit a fuse and a MOV.
there were some indicator LEDs on the front plate. they were all burnt and I replaced them only to find that they were still not working. there were 180 ohm resistors in series with all of them and upon measurement I found that ALL the resistors were damaged (circuit interrupted). NONE of the resistors showed any usual sign of physical damage. basically all the resistors that were connected to the unprotected part of the amp were damaged without any optical trace.
this is the very first time something like this happens to me, I've had tons of cooked resistors (physically burnt) in the past. and the large number of them presenting the same type of failure makes me wonder...
there were some indicator LEDs on the front plate. they were all burnt and I replaced them only to find that they were still not working. there were 180 ohm resistors in series with all of them and upon measurement I found that ALL the resistors were damaged (circuit interrupted). NONE of the resistors showed any usual sign of physical damage. basically all the resistors that were connected to the unprotected part of the amp were damaged without any optical trace.
this is the very first time something like this happens to me, I've had tons of cooked resistors (physically burnt) in the past. and the large number of them presenting the same type of failure makes me wonder...
I have seen this behaviour of resistors in an overcurrent fault at work once before.
When I was looking up the failed parts in the bill of materials, I found out that the resistors weren't ordinary resistors but fusible resistors.
If you have the service manual of your amp, the bill of materials should list them as fusibles, and often in the schematic an exclamation mark is printed next to them to indicate they MUST be replaced by identical type.
When I was looking up the failed parts in the bill of materials, I found out that the resistors weren't ordinary resistors but fusible resistors.
If you have the service manual of your amp, the bill of materials should list them as fusibles, and often in the schematic an exclamation mark is printed next to them to indicate they MUST be replaced by identical type.
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